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DAVID MALAN: Hi.

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My name is David Malan,
and this is CS50.

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So I absolutely love this course.

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This, for me, is my dream job, to
be honest, now teaching this course,

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because I took this
course myself about 11,

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12 years ago when I was a sophomore.

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And I actually came
in to Harvard not even

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as a computer science major minded
person, but I started off as gov.

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I had exited high school
thinking I liked history,

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I liked constitutional law.

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And so the natural
progression once I got here

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seemed to be to go into
the gov department.

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And I spent freshman
fall, freshman spring,

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even sophomore fall biting off a lot of
the requirements for that department.

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And it was really at the last minute,
shopping period during sophomore fall,

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that I decided, you
know what, I'm actually

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going to give this course a shot.

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Because I've always been one
of those geeky kind of kids

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and I always liked
playing with computers,

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grew up with a Commodore 64 and an Apple
2 and a Mac and then PCs, eventually.

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But computer science and
computer science courses, I mean,

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I actually remember looking
around at some of my friends,

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actually, in high school who
were taking AP computer science,

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and I thought they were a
bunch of geeks, to be honest,

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and I didn't actually even
consider taking that course myself.

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And freshman year when I arrived here,
I still was of the certainly technically

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minded sorts, but this course
CS50 had this reputation,

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and it had it for years of being
ridiculously daunting, ridiculously

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time-consuming, and overall scary.

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And that-- quite
honestly-- that reputation

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scared me away from taking
that course my freshman fall.

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And this was, mind you,
I was working as a UA.

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And if a UA--

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a user assistant-- if
a user assistant was

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sort of disinclined to take
this course, well, I mean,

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maybe there was something to that.

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But finally, sophomore
fall, I decided, you

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know what, I'm still going to
continue on this gov track,

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I'm going to enroll in
CS50, pass, fail, because it

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was going to take the edge off the
course, give me a bit of freedom.

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And at the last day,
literally the last moment,

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I ended up going to the
registrar and filling out

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whatever paperwork was required
to switch myself to a grade.

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And I ended up switching that winter
to computer science as my major.

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And fast forward several
years, I ended up

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in graduate school in computer
science, and then of all things,

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I ended up, up here.

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And it is really a
weird role reversal now

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to be up here, because it was precisely
this course taught by a brilliant man,

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at the time, Brian Kernighan
who was visiting, and is

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a pioneer in the world
of computer science, that

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turned me on to computer
science and actually got me

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into this kind of stuff.

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And then it's not to say that
students who take this course

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all exit as computer science majors.

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The computer science majors among you
are by far the minority in this course,

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in the single digits, maybe 10%.

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Most of the students in this
course are, in fact, non majors.

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So why might that be?

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Well, you often hear whether
it's in high school or college

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that this is one of those courses
that teaches you how to think,

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problem-solving skills.

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But you know what?

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There's actually something to that.

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I can genuinely say, certainly as
more and more years have passed

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and the more comfortable I've
gotten with this kind of stuff,

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I absolutely approach life, dare
say, a little more methodically

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or algorithmically, at
least in terms of what

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goes on in my head when I'm
thinking about some problem

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or I'm trying to give someone
directions, for instance.

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I'm much more precise these days.

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But even more than
that, and the fun side

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effect of courses like
those in computer science,

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is that this computer that all of you
have, either in your laps right now

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or on your desks at home,
you, for the most part,

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use these computers in such a way
that you can only do with them what

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someone else has empowered you to do.

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Whether it's Apple or
Microsoft or whoever

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wrote some program that
you're particularly a fan of.

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And so when you finally, though, take a
course, like in computer science, CS50

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and actually learn how to
program, it actually opens up

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some really interesting, geeky,
but dare say fun opportunities.

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In fact, at the risk of living
a little too long in the past,

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I thought I'd pull up one
thing that I'm very proud of.

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And perhaps I've beaten this to--

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I'm beating a dead horse for
some number of years here.

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But when I was an
undergrad, there really--

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well, there was an internet,
so I can't go that far,

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but there was no way of checking
shuttle schedules at the time other

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than that printed piece of paper.

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And this was kind of
a nuisance, of course,

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to have to pull up a piece of paper to
find out where you can go on campus.

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And so at the time,
students were really using

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what was called fas.harvard.edu, which
still exists, but most of your friends

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who aren't in this room
right now will never

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SSH to ffs.harvard.edu, so to
speak, though you all soon will.

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But I wrote this program after taking 50
computer science 51, kind of on a whim.

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And that program was
actually not this one,

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but it was this stupid
program called Menu Boy.

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So at the time, back in the
day, there was like 495 menu,

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which I don't know if it still exists.

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Perhaps one of you can try
this later and see who you get.

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But it was this recorded voice from
dining services that would tell you,

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it would recite to you every
morning what was on the day's menus.

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And I'm like, all right,
well Menu Man already

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exists so I went with me Menu Boy.

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And it was this Unix program that
my pretty much, me, my roommate,

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and my other roommate could pull
up on a computer in our dorm room

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and check what was on
the dining hall menu.

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Well, mildly useful.

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That sort of evolved into what
was called Weather Boy, which

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did as you might expect.

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That one was kind of
a bust since we just

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used to look outside the window and
Mather Tower and that was sufficient.

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So finally, I hit on, how
about shuttle schedules?

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The irony being, I never
actually took the shuttle myself.

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But long story short, I sat down
with the printed shuttle schedule

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and I said, all right, I'm going to do
this just because I can, and invented

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a program that I eventually
ported to the web,

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but it still looked like this in
a nutshell, as you might expect.

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You can, via a series
of menus or shortcuts,

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say, all right, I'm in Memorial Hall,
I want to go to the quad after this.

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Well, there we go.

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If you're already sick of this course,
you can go in one minute's time

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and catch the shuttle out of here.

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And this thing updates
itself every minute.

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So that's all fine and good, but
not terribly sexy in 2007 and 2008.

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So the next evolution of this for me
was not so much the web-based version,

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but was a version that actually
allowed you to text message thing.

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So if you want to play
along at home here,

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if you have a cell phone,
if you dial 41-411.

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And then what you have to type
is a text message as follows--

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S boy, for Shuttle Boy, and then the
first few letters of where you are

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and where you want to go.

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So mem quad for instance,
is what I'll type in here.

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If you can actually see this here.

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S Boy mem quad, it's a little small.

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But if you go ahead then and
hit send, if this program

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I wrote last year for
CS50 has not actually

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broken in the past few minutes.

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Let's see.

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Whatever that is, we'll
apparently tick the time away.

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And oh, there we go.

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And apparently, if you can
read this, there you go.

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S Boy says it's 1:21 and you can go
mem hall to quad in 29 minutes at 1:50,

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so we apparently just missed
that last shuttle bus.

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All right.

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So all fine and good, but come
on, we can do better than this.

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And so just because I could and just
because I had these skills finally

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and this, perhaps, disposition,
I thought, you know what?

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There's so much freely available
information out there now.

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The shuttle buses as
of last year started

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having GPS transponders so that the
shuttle services folks could track them

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on campus.

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And so I thought, you
know what, I'm going

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to see if I can tap into that data
feed, integrate it in mash up form

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with Google Maps, and
late, one sad night,

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was born Shuttle Boy the GPS version.

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And I will be the
first to admit, I still

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think it's the coolest thing
that those red dots move

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as the shuttle buses move on campus.

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Now it's not perfect.

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So you'll quickly learn in
this course what a bug is.

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And so for instance, if I
actually zoom in on this, yeah,

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the shuttle is not right on
Cambridge Common right now.

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So it's not quite perfect,
but I was at least still

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kind of proud of that myself.

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So beyond these kinds of fun things
that come by nature with the ability

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to program, I mean, you
genuinely learn how to think

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and how to approach
problems differently.

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Because a lot of what computer science
is, it's not actually programming,

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even though I've taught
entire courses in the past

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and we've surveyed students
at the end of the semester,

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what did you get out of this
course, what did you learn?

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And many of them in
many courses have been--

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I learned how to program in C, I
learned how to program in Java,

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and that's fine, and that's
true, and that's valuable,

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and that's interesting, but
it's not necessarily everything.

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Because one of the more interesting
aspects of a course like this

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is that in teaching you
how to think differently,

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it opens you to the possibilities of
solving problems more effectively,

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solving problems more
efficiently, saving yourself time

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by actually writing
software or making hardware

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that does things that would take a human
much more time to solve on their own.

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So case in point, I thought maybe
we could humor ourselves as follows.

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So a natural thing at
the start of a semester

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is you've got to take attendance
or you've got to take roll.

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So you start counting in the top right.

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One, two, three, four, five.

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All right, so we'll be here
all day using this method.

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So what's a marginally
better improvement on that?

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How could I count students
in this room more quickly?

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Take a picture and do it later, sure.

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What else you got?

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What's that?

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So count them at the door.

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In retrospect, that too
would have been better.

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What else?

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Something simple.

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Yeah?

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What's that?

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Oh, have everyone text a number
and let my computer count.

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All right, so that's
even more sophisticated.

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I'm going to go with what
I learned in grade school

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and just count people two at once.

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So two, four, six, eight.

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Don't try too hard.

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I know, first day at Harvard here,
but we don't need to go too far here.

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And incidentally, let's get
this part out of the way.

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So this is a ridiculously
large, if not intimidating room,

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and we have microphones
set up down there.

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I'd much prefer if we can try to
turn this course into something that

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is a bit chatty, that is a bit
informal, because I can't even

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imagine the idea, of as a
student, and even now as an adult,

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walking up to a microphone to
admit to hundreds of people,

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so I'm kind of confused, I don't
really know what you just said.

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I don't see these kinds of
microphones working too well.

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You're welcome to use
them, but let's see if we

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can do this a little more intimately.

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So my conclusion was I'm going
to count people in two's.

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So two, four, six, eight.

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All right, so that's clearly
better, because it's twice as fast.

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But if we think a little harder about
this problem of counting students,

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can we do even better than that?

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I mean, wouldn't it
be a really cool thing

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if instead of just doubling
the speed with which

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we can count students, or equivalently,
halving the amount of time

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it takes to do so.

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What if our algorithm, our approach,
our method, not only started off faster,

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but as I went, it got faster
and faster and faster?

233
00:10:59,237 --> 00:11:02,070
I mean, it'd be kind of neat if I
could start counting in twos, then

234
00:11:02,070 --> 00:11:04,278
very quickly get comfortable
with that start counting

235
00:11:04,278 --> 00:11:06,990
in fours, then maybe
eights, then maybe sixteens,

236
00:11:06,990 --> 00:11:09,000
and eventually gets a little confusing.

237
00:11:09,000 --> 00:11:11,820
But if you could build up
momentum like this, bam,

238
00:11:11,820 --> 00:11:14,910
we would be done counting
students pretty darn fast.

239
00:11:14,910 --> 00:11:17,910
So in fact, I can't quite
do that on my own fingers.

240
00:11:17,910 --> 00:11:22,530
So what I did was went ahead and put
together an algorithm on paper here.

241
00:11:22,530 --> 00:11:26,190
Because there's this other opportunity
in this room to solve this problem.

242
00:11:26,190 --> 00:11:30,090
We have not just me as the single
brain or CPU in this room capable

243
00:11:30,090 --> 00:11:33,570
of independent thought, but we
have a couple hundred of you here

244
00:11:33,570 --> 00:11:36,280
who can presumably be
helping me out with this.

245
00:11:36,280 --> 00:11:39,400
And so allow me to ask two things.

246
00:11:39,400 --> 00:11:41,442
First-- this is also a
very impersonal room,

247
00:11:41,442 --> 00:11:43,650
you probably don't know all
of the people around you.

248
00:11:43,650 --> 00:11:46,170
So take a moment, right
now, if you could,

249
00:11:46,170 --> 00:11:49,140
turn to the person on your
left, to the right, say hello,

250
00:11:49,140 --> 00:11:52,607
house, concentration, all
that stuff, and make a friend.

251
00:11:52,607 --> 00:11:56,086
[INTERPOSING VOICES]

252
00:11:56,086 --> 00:12:22,217


253
00:12:22,217 --> 00:12:23,175
DAVID MALAN: All right.

254
00:12:23,175 --> 00:12:26,830


255
00:12:26,830 --> 00:12:27,795
All right.

256
00:12:27,795 --> 00:12:31,270


257
00:12:31,270 --> 00:12:31,770
OK.

258
00:12:31,770 --> 00:12:36,300


259
00:12:36,300 --> 00:12:38,370
Yes, they're very
interesting next to you.

260
00:12:38,370 --> 00:12:39,610
OK, now back here.

261
00:12:39,610 --> 00:12:40,110
All right.

262
00:12:40,110 --> 00:12:43,080
So you now have a friend, first
of all, in computer science 50.

263
00:12:43,080 --> 00:12:45,540
Now it's going to get a
little more awkward, again,

264
00:12:45,540 --> 00:12:48,660
for just a moment, because I need
you all to humor me for a moment

265
00:12:48,660 --> 00:12:50,130
and please stand up.

266
00:12:50,130 --> 00:12:53,880
Step one, stand up if you would.

267
00:12:53,880 --> 00:12:56,580
So there are more of you
than there are of me.

268
00:12:56,580 --> 00:12:58,980
You are all capable of
counting, presumably, therefore

269
00:12:58,980 --> 00:13:01,753
you are capable of executing
this computer program.

270
00:13:01,753 --> 00:13:02,920
It's pretty straightforward.

271
00:13:02,920 --> 00:13:05,550
It's only got five or so steps here.

272
00:13:05,550 --> 00:13:09,270
Four, if whoever standing in back
doesn't move over to the side.

273
00:13:09,270 --> 00:13:10,320
Step one is stand up.

274
00:13:10,320 --> 00:13:14,517
Step two, think to yourself,
I am the number one.

275
00:13:14,517 --> 00:13:16,350
It's probably not a
stretch for some of you.

276
00:13:16,350 --> 00:13:18,930
All right.

277
00:13:18,930 --> 00:13:22,680
Step three, go ahead and pair up
with someone standing near you,

278
00:13:22,680 --> 00:13:25,380
add your numbers together, take
that sum as your new number.

279
00:13:25,380 --> 00:13:28,610


280
00:13:28,610 --> 00:13:29,900
A little sanity check.

281
00:13:29,900 --> 00:13:34,670
If you're following along correctly,
everybody's now the number two.

282
00:13:34,670 --> 00:13:36,470
One of you should go ahead and sit down.

283
00:13:36,470 --> 00:13:49,570


284
00:13:49,570 --> 00:13:52,330
And repeat per these directions.

285
00:13:52,330 --> 00:14:02,190


286
00:14:02,190 --> 00:14:05,775
If you're standing awkwardly, look
for someone you can pair up with.

287
00:14:05,775 --> 00:14:24,760


288
00:14:24,760 --> 00:14:26,725
Should be just a couple
of people standing.

289
00:14:26,725 --> 00:14:40,490


290
00:14:40,490 --> 00:14:42,420
A couple people left.

291
00:14:42,420 --> 00:14:49,350


292
00:14:49,350 --> 00:14:50,105
Almost there.

293
00:14:50,105 --> 00:15:00,512


294
00:15:00,512 --> 00:15:01,220
What did you get?

295
00:15:01,220 --> 00:15:05,940


296
00:15:05,940 --> 00:15:06,510
All right.

297
00:15:06,510 --> 00:15:11,440
There should be just one awkward
person standing before long.

298
00:15:11,440 --> 00:15:11,940
All right.

299
00:15:11,940 --> 00:15:15,255
These guys are using paper and
pencil, that is not very Harvard.

300
00:15:15,255 --> 00:15:17,910


301
00:15:17,910 --> 00:15:19,830
That's OK.

302
00:15:19,830 --> 00:15:20,850
Just kidding.

303
00:15:20,850 --> 00:15:22,745
I'd be doing it, too.

304
00:15:22,745 --> 00:15:23,370
What do we got?

305
00:15:23,370 --> 00:15:24,325
One here, one here.

306
00:15:24,325 --> 00:15:25,950
We need a couple of people to pair off.

307
00:15:25,950 --> 00:15:27,040
One here.

308
00:15:27,040 --> 00:15:27,660
Three.

309
00:15:27,660 --> 00:15:28,350
There's three of you.

310
00:15:28,350 --> 00:15:29,642
All right, combine two numbers.

311
00:15:29,642 --> 00:15:32,755


312
00:15:32,755 --> 00:15:33,255
72.

313
00:15:33,255 --> 00:15:37,160


314
00:15:37,160 --> 00:15:38,540
Oh, OK.

315
00:15:38,540 --> 00:15:40,310
And?

316
00:15:40,310 --> 00:15:41,660
113.

317
00:15:41,660 --> 00:15:43,460
So what's that?

318
00:15:43,460 --> 00:15:44,540
Oh, and 119.

319
00:15:44,540 --> 00:15:45,290
So what do we got?

320
00:15:45,290 --> 00:15:46,850
What's the total.

321
00:15:46,850 --> 00:15:50,270
I'm not going to embarrass
myself in doing it up here.

322
00:15:50,270 --> 00:15:52,310
What's our total?

323
00:15:52,310 --> 00:15:53,240
What's the total?

324
00:15:53,240 --> 00:16:01,110


325
00:16:01,110 --> 00:16:03,180
What's that?

326
00:16:03,180 --> 00:16:06,510
So the total comes to-- thanks
to our diligent teaching staff--

327
00:16:06,510 --> 00:16:09,690
399.

328
00:16:09,690 --> 00:16:11,310
So close to 400.

329
00:16:11,310 --> 00:16:16,260
And that probably took
less time than it would--

330
00:16:16,260 --> 00:16:17,019
oh.

331
00:16:17,019 --> 00:16:20,442
[APPLAUSE]

332
00:16:20,442 --> 00:16:28,760


333
00:16:28,760 --> 00:16:30,830
400 it is.

334
00:16:30,830 --> 00:16:34,080
So what can we take away from that?

335
00:16:34,080 --> 00:16:35,940
Well, how many steps did that take?

336
00:16:35,940 --> 00:16:39,830
Well, granted, each of these
steps is like one big step.

337
00:16:39,830 --> 00:16:41,270
It's kind of like one iteration.

338
00:16:41,270 --> 00:16:45,260
You went through the process of finding
someone, pairing up, taking on the sum

339
00:16:45,260 --> 00:16:46,590
and then sitting down.

340
00:16:46,590 --> 00:16:49,520
So if we group that together,
conceptually, it's just one step.

341
00:16:49,520 --> 00:16:52,640
Let's ask ourselves, how
many such steps were there?

342
00:16:52,640 --> 00:16:56,015
Well, maybe we can answer this
by building from the ground up.

343
00:16:56,015 --> 00:16:57,890
This is Excel, I'm just
going to use it to do

344
00:16:57,890 --> 00:16:59,670
some simple graphing for a moment.

345
00:16:59,670 --> 00:17:01,610
So if there's two of
you, it really only would

346
00:17:01,610 --> 00:17:05,450
have taken one such step,
one such loop or iteration,

347
00:17:05,450 --> 00:17:09,170
because the two people pair up,
one sits down, done, so one step.

348
00:17:09,170 --> 00:17:11,900
If instead, though, there
were, say, four of you,

349
00:17:11,900 --> 00:17:15,349
well, that too would still only
take not four steps, but just

350
00:17:15,349 --> 00:17:19,710
two steps, because four people would
pair, the two pairs would pair, done.

351
00:17:19,710 --> 00:17:21,390
So just a couple steps there.

352
00:17:21,390 --> 00:17:23,450
So if this number then
increases-- so I'm

353
00:17:23,450 --> 00:17:26,150
going to do a little formula just
to save myself some time here.

354
00:17:26,150 --> 00:17:30,230
If this pattern increases or
continues along these lines--

355
00:17:30,230 --> 00:17:34,410
whoops-- what just happened?

356
00:17:34,410 --> 00:17:41,160
If this pattern continues along these
lines where this is A three times two,

357
00:17:41,160 --> 00:17:42,060
all right.

358
00:17:42,060 --> 00:17:44,000
Let's copy that.

359
00:17:44,000 --> 00:17:45,150
Paste there.

360
00:17:45,150 --> 00:17:45,900
There we go.

361
00:17:45,900 --> 00:17:48,782
So if that pattern continues,
but in the right hand column,

362
00:17:48,782 --> 00:17:50,990
this just takes us one step,
this takes us two steps,

363
00:17:50,990 --> 00:17:52,470
this takes us three steps.

364
00:17:52,470 --> 00:17:59,450
So this takes us, A three
plus one and B three plus one,

365
00:17:59,450 --> 00:18:00,880
that pattern continues as follows.

366
00:18:00,880 --> 00:18:04,130
So in the left hand column we've got how
many students there are, potentially,

367
00:18:04,130 --> 00:18:06,600
the right hand column,
the total number of steps.

368
00:18:06,600 --> 00:18:07,820
And this is kind of powerful.

369
00:18:07,820 --> 00:18:08,690
I mean, look at what it's saying.

370
00:18:08,690 --> 00:18:11,030
If we've got roughly 400
students, so somewhere

371
00:18:11,030 --> 00:18:14,720
between 256 and 512
students, that only took--

372
00:18:14,720 --> 00:18:19,820
felt like longer-- but eight steps,
eight such iterations, maybe nine.

373
00:18:19,820 --> 00:18:22,970
Well, let's take a look at what this
actually feels like in the long run.

374
00:18:22,970 --> 00:18:25,970
If I just quickly grab these numbers--
and this is not the kind of stuff

375
00:18:25,970 --> 00:18:28,910
we'll be doing in this course,
using things like word and Excel,

376
00:18:28,910 --> 00:18:31,250
but it's useful just to
illustrate this for a moment.

377
00:18:31,250 --> 00:18:34,130
I'm going to produce one of
these little plots, new sheet,

378
00:18:34,130 --> 00:18:35,870
just to show you what this looks like.

379
00:18:35,870 --> 00:18:39,200
And what we have on the x-axis
here is number of students,

380
00:18:39,200 --> 00:18:42,290
on the y-axis, the total
number of loops or iterations.

381
00:18:42,290 --> 00:18:43,520
Notice what happens.

382
00:18:43,520 --> 00:18:46,070
Like, it kind of takes a long time for--

383
00:18:46,070 --> 00:18:49,070
relatively speaking-- for
small groups of students.

384
00:18:49,070 --> 00:18:51,680
But look at what
happens in the long run.

385
00:18:51,680 --> 00:18:55,490
It feels like this algorithm,
this approach, this divide

386
00:18:55,490 --> 00:18:58,640
and conquer strategy
seems to gain speed.

387
00:18:58,640 --> 00:19:01,850
The bigger the problem gets, the
more effective the algorithm becomes.

388
00:19:01,850 --> 00:19:05,900
If we're out at say
four billion students--

389
00:19:05,900 --> 00:19:08,780
that's a big room-- so
four billion students.

390
00:19:08,780 --> 00:19:12,590
How many steps does it take to
actually implement this algorithm?

391
00:19:12,590 --> 00:19:13,730
32.

392
00:19:13,730 --> 00:19:19,070
There's only 32 such steps to count
four billion students, logistical issues

393
00:19:19,070 --> 00:19:19,850
aside.

394
00:19:19,850 --> 00:19:22,700
Well, let's see if we can't make
this a little more concrete.

395
00:19:22,700 --> 00:19:25,250
I don't really like to
reuse material, but this one

396
00:19:25,250 --> 00:19:27,255
seemed to be a popular one last year.

397
00:19:27,255 --> 00:19:28,880
This is a pretty big phone book, right?

398
00:19:28,880 --> 00:19:31,070
It's a few thousand pages.

399
00:19:31,070 --> 00:19:35,205
And this lends itself to this
same thinking, the same divide

400
00:19:35,205 --> 00:19:36,080
and conquer approach.

401
00:19:36,080 --> 00:19:39,560
Suppose that I wanted to
look up Drew Foust-- so

402
00:19:39,560 --> 00:19:41,330
[INAUDIBLE] Foust in this phone book.

403
00:19:41,330 --> 00:19:43,070
Granted, it's the yellow pages,
just she's probably not there.

404
00:19:43,070 --> 00:19:44,695
But we'll pretend it's the White pages.

405
00:19:44,695 --> 00:19:48,380
How would you, as a fairly
intelligent human being,

406
00:19:48,380 --> 00:19:52,610
go about finding someone like
Drew Faust in the book here?

407
00:19:52,610 --> 00:19:53,990
Yes?

408
00:19:53,990 --> 00:19:54,680
What's that?

409
00:19:54,680 --> 00:19:55,790
Oh, page one.

410
00:19:55,790 --> 00:19:57,750
We're definitely going
with the semi approach.

411
00:19:57,750 --> 00:20:00,410
So page one, we have the A's.

412
00:20:00,410 --> 00:20:02,090
Page two, still the A's.

413
00:20:02,090 --> 00:20:03,830
Page three, and dot, dot, dot.

414
00:20:03,830 --> 00:20:07,220
So right, the worst case scenario
there, whoever I'm looking for

415
00:20:07,220 --> 00:20:10,460
might actually be at the end of the
phone book, certainly not on page one,

416
00:20:10,460 --> 00:20:12,740
and that's going to take
a good number of steps.

417
00:20:12,740 --> 00:20:16,670
Probably a slightly more clever
person is going to do what?

418
00:20:16,670 --> 00:20:19,323


419
00:20:19,323 --> 00:20:21,490
Right, you're going to
probably start in the middle,

420
00:20:21,490 --> 00:20:24,100
if only because it's easy to
open a phone book to the middle.

421
00:20:24,100 --> 00:20:26,387
You're going to glance, it
and be like, oh, M happened

422
00:20:26,387 --> 00:20:27,970
to be in the middle of the phone book.

423
00:20:27,970 --> 00:20:29,870
Well, what am I going to do next?

424
00:20:29,870 --> 00:20:33,257
Well, I already know that this was
a pretty big problem a moment ago.

425
00:20:33,257 --> 00:20:35,590
But I already know that Drew
is going to be to the left.

426
00:20:35,590 --> 00:20:39,283
I'm at the M's, which means
she's not going to be over here.

427
00:20:39,283 --> 00:20:41,200
And this is why everyone
liked this last year.

428
00:20:41,200 --> 00:20:46,580
So we can literally throw
away half of the problem.

429
00:20:46,580 --> 00:20:47,710
And now it's half as big.

430
00:20:47,710 --> 00:20:48,830
Well, what do we do next?

431
00:20:48,830 --> 00:20:53,240
Well, we can resort to that page
flipping approach, or we can repeat,

432
00:20:53,240 --> 00:20:55,540
we can recurse and do
the same thing again.

433
00:20:55,540 --> 00:20:59,050
Smack dab into the middle
here, I happened to end up at--

434
00:20:59,050 --> 00:21:02,650
freebee-- we happen to end up in
the middle here, this is the Cs.

435
00:21:02,650 --> 00:21:06,280
So yet again, I can
literally take a bite out

436
00:21:06,280 --> 00:21:09,880
of this problem equal to half of
its current size, throw it away.

437
00:21:09,880 --> 00:21:12,520
And in just two steps, we've
halved and then halved--

438
00:21:12,520 --> 00:21:15,200
which mean quartered the
size of this problem.

439
00:21:15,200 --> 00:21:17,380
So now extrapolate to
some of the data here.

440
00:21:17,380 --> 00:21:19,540
If that phone book were
actually ridiculously

441
00:21:19,540 --> 00:21:23,890
large with four billion
entries, four billion pages,

442
00:21:23,890 --> 00:21:28,000
how many times am I going to split
and throw half of the phone book away?

443
00:21:28,000 --> 00:21:29,560
Only 32 times.

444
00:21:29,560 --> 00:21:33,800
What if there are not four billion,
but eight billion people in that phone

445
00:21:33,800 --> 00:21:34,300
book?

446
00:21:34,300 --> 00:21:35,930
Eight billion pages.

447
00:21:35,930 --> 00:21:38,930
Well, 33 steps.

448
00:21:38,930 --> 00:21:40,570
And that's a really powerful thing.

449
00:21:40,570 --> 00:21:43,690
And that just hints at the
types of design problems

450
00:21:43,690 --> 00:21:48,460
that come up in computer science and the
types of work that ultimately come out,

451
00:21:48,460 --> 00:21:50,140
as we'll see, the course's problem sets.

452
00:21:50,140 --> 00:21:55,070
Now it's not all serious and
focused on clever approaches.

453
00:21:55,070 --> 00:21:58,330
So we have made a conscious
decision this semester

454
00:21:58,330 --> 00:22:04,310
to introduce as much geek
culture to Harvard as possible.

455
00:22:04,310 --> 00:22:07,414
[APPLAUSE]

456
00:22:07,414 --> 00:22:09,940


457
00:22:09,940 --> 00:22:14,340
Josiah Quincy and James Otis would be
so pleased to be next to this right now.

458
00:22:14,340 --> 00:22:19,130
So it all began, of course, 10 years
ago when Shuttle Boy entered the Harvard

459
00:22:19,130 --> 00:22:19,770
lexicon.

460
00:22:19,770 --> 00:22:24,710
Now we're going to try to push some
lolcats onto the community here.

461
00:22:24,710 --> 00:22:27,350
I'll refer you to Wikipedia
for more of a backdrop here.

462
00:22:27,350 --> 00:22:30,008
But just in the spirit
of this same, you know

463
00:22:30,008 --> 00:22:33,050
what, I'm going to do something just
because it's neat, just because it's

464
00:22:33,050 --> 00:22:34,370
fun, just because I can.

465
00:22:34,370 --> 00:22:37,460
And along the way, I'm sure I'll
encounter some interesting problems.

466
00:22:37,460 --> 00:22:41,720
I, in a moment, or in an hour of
severe procrastination last night,

467
00:22:41,720 --> 00:22:45,350
decided what our website needs in
the course is a lolcat of the day.

468
00:22:45,350 --> 00:22:49,010
So this didn't exist last year
and this didn't exist on Saturday.

469
00:22:49,010 --> 00:22:52,580
But I decided, who's not
going to click on the lolcat?

470
00:22:52,580 --> 00:22:57,950
And I will argue, I will put forth,
that I bet a non-trivial number of you

471
00:22:57,950 --> 00:23:00,830
make a habit, every time you start
pulling up the course's website,

472
00:23:00,830 --> 00:23:04,130
you're going to click on that link,
even though it really does nothing other

473
00:23:04,130 --> 00:23:05,270
than show you, right?

474
00:23:05,270 --> 00:23:08,450


475
00:23:08,450 --> 00:23:10,820
So stupid.

476
00:23:10,820 --> 00:23:12,210
But how did I do this?

477
00:23:12,210 --> 00:23:15,290
Well, I asked a friend of mine,
all right, where can I get lolcats?

478
00:23:15,290 --> 00:23:18,680
Well, it turns out that one of
these sources, the canonical source,

479
00:23:18,680 --> 00:23:23,030
is icanhascheezburger.com.

480
00:23:23,030 --> 00:23:27,530
So that led me to this website here,
which, if you really have a lot of time

481
00:23:27,530 --> 00:23:29,510
to kill, you can search
through-- let's see

482
00:23:29,510 --> 00:23:32,690
if we go to the bottom,
the 90 to infinity

483
00:23:32,690 --> 00:23:35,730
and beyond pages that have
been posted here over time.

484
00:23:35,730 --> 00:23:38,540
But what I noticed, what caught
my eye at the top of this page

485
00:23:38,540 --> 00:23:39,800
is this little thing here.

486
00:23:39,800 --> 00:23:41,633
So subscribe to an RSS feed.

487
00:23:41,633 --> 00:23:44,300
Now this is something some of you
might already use, some of you

488
00:23:44,300 --> 00:23:47,540
might have at least seen this icon,
even on cnn.com, New York Times,

489
00:23:47,540 --> 00:23:49,520
reputable sites, it's not all geekery.

490
00:23:49,520 --> 00:23:53,060
And long story short, what an
RSS feed is just a big text

491
00:23:53,060 --> 00:23:57,108
file, an XML file,
similar in spirit to HTML,

492
00:23:57,108 --> 00:23:59,900
which is something we'll use later
in the course to make web pages.

493
00:23:59,900 --> 00:24:03,170
And inside this big text file,
it's just a lot of links.

494
00:24:03,170 --> 00:24:08,178
Links to the current lolcat of the
day, links to yesterday's lolcat

495
00:24:08,178 --> 00:24:08,720
and so forth.

496
00:24:08,720 --> 00:24:10,428
And I realized, you
know what, if there's

497
00:24:10,428 --> 00:24:14,120
this feed that the website
itself lets people subscribe to,

498
00:24:14,120 --> 00:24:17,420
well, maybe I can write a little
program that just downloads that feed

499
00:24:17,420 --> 00:24:21,260
downloads, simulating a
user clicking that link,

500
00:24:21,260 --> 00:24:25,634
analyzes all of that text looking
for URLs, things like http, colon,

501
00:24:25,634 --> 00:24:29,150
slash, slash, grab that
image and then embed it

502
00:24:29,150 --> 00:24:31,760
into our own website, along
with a couple of more links,

503
00:24:31,760 --> 00:24:34,190
so it then links back
to the original page.

504
00:24:34,190 --> 00:24:38,600
And long story short, that's
all it took, was an idea and--

505
00:24:38,600 --> 00:24:40,910
make it really juicy--

506
00:24:40,910 --> 00:24:43,640
an idea and the means to
actually implement it.

507
00:24:43,640 --> 00:24:46,520
And thus was born lolcat of the day.

508
00:24:46,520 --> 00:24:50,700
So more of those on an
increasingly frequent basis.

509
00:24:50,700 --> 00:24:52,860
So who is in this class?

510
00:24:52,860 --> 00:24:56,120
So there has been, for years,
a misconception, for instance,

511
00:24:56,120 --> 00:24:59,840
that the course is filled only with
those more comfortable, so to speak.

512
00:24:59,840 --> 00:25:02,720
We adopted these
euphemistic labels last year

513
00:25:02,720 --> 00:25:05,120
to refer to those students
who were, quite matter

514
00:25:05,120 --> 00:25:08,570
of factly, less comfortable in a
course like this with computers,

515
00:25:08,570 --> 00:25:11,810
with the internet, with the idea of
even being in a computer science course.

516
00:25:11,810 --> 00:25:15,170
Then we labeled the opposite,
which were those more comfortable.

517
00:25:15,170 --> 00:25:18,770
Students, like many among you, who've
taken AP computer science, who,

518
00:25:18,770 --> 00:25:22,040
like me, grew up with computers
and have been raring to go

519
00:25:22,040 --> 00:25:24,290
with an actual computer science degree.

520
00:25:24,290 --> 00:25:27,350
And then there's many of you
who are somewhere in between.

521
00:25:27,350 --> 00:25:30,750
And being computer scientists, we
like to collect data, analyze data,

522
00:25:30,750 --> 00:25:34,283
and then actually bolster our
conjectures with actual numbers.

523
00:25:34,283 --> 00:25:34,950
And here you go.

524
00:25:34,950 --> 00:25:38,930
So as of last fall, 2007, the
percentages of students in the course

525
00:25:38,930 --> 00:25:40,370
roughly broke down as follows.

526
00:25:40,370 --> 00:25:44,990
30%, certainly non-negligible, describe
themselves as less comfortable,

527
00:25:44,990 --> 00:25:48,320
the sort who during shopping period
were not coming back Wednesday.

528
00:25:48,320 --> 00:25:50,780
But fortunately, 30% of them did.

529
00:25:50,780 --> 00:25:53,670
I'm among those more comfortable, 20%.

530
00:25:53,670 --> 00:25:57,230
So also non-trivial, but certainly
not even close to a majority

531
00:25:57,230 --> 00:26:00,620
of the students in the class, because
the majority really is made up of about

532
00:26:00,620 --> 00:26:01,230
half--

533
00:26:01,230 --> 00:26:04,673
a majority of the class is made up of
people who are somewhere in between.

534
00:26:04,673 --> 00:26:07,340
Certainly not the least comfortable,
certainly not the savviest,

535
00:26:07,340 --> 00:26:11,450
but they're somewhere
in between the two,

536
00:26:11,450 --> 00:26:14,400
and we suspect that those
numbers would play out the same.

537
00:26:14,400 --> 00:26:17,570
So those of you who are feeling
a little less comfortable,

538
00:26:17,570 --> 00:26:20,120
I thought I'd try to put
you at ease, even before we

539
00:26:20,120 --> 00:26:21,870
dive into things more sophisticated.

540
00:26:21,870 --> 00:26:24,350
This, of course, if you
know, is Senator Ted Stevens

541
00:26:24,350 --> 00:26:26,510
of Alaska, who had the
misfortune of being

542
00:26:26,510 --> 00:26:28,520
lampooned by Jon Stewart and the likes.

543
00:26:28,520 --> 00:26:35,090
A couple of years ago when he was quoted
during a very, very boisterous speech

544
00:26:35,090 --> 00:26:37,755
about things related to the internet.

545
00:26:37,755 --> 00:26:40,130
So what I thought we'd do is
sort of establish a baseline

546
00:26:40,130 --> 00:26:43,730
as to what it means to really be less
comfortable, because I think that will

547
00:26:43,730 --> 00:26:46,040
perhaps put a few of you at ease.

548
00:26:46,040 --> 00:26:46,940
So let me grab this.

549
00:26:46,940 --> 00:26:48,740
It's about a three-minute clip.

550
00:26:48,740 --> 00:26:52,590
Let's go ahead and
pull up the following.

551
00:26:52,590 --> 00:26:57,480


552
00:26:57,480 --> 00:26:58,620
[VIDEO PLAYBACK]

553
00:26:58,620 --> 00:27:02,685
- Oh, we got a bombshell
for you tonight.

554
00:27:02,685 --> 00:27:04,180
Oh, I am delighted, here.

555
00:27:04,180 --> 00:27:07,520


556
00:27:07,520 --> 00:27:09,110
Today's show is a good one.

557
00:27:09,110 --> 00:27:12,510
Shawn Wayans, Shawn
Wayans will be joining us.

558
00:27:12,510 --> 00:27:14,753
We're very excited about that.

559
00:27:14,753 --> 00:27:17,670
But I want to talk to you about this
exciting thing I have discovered.

560
00:27:17,670 --> 00:27:19,020
I want to talk to you
tonight about the internet.

561
00:27:19,020 --> 00:27:20,320
I'm going out on a limb here.

562
00:27:20,320 --> 00:27:22,737
I'm going to stand up and be
one of the first guys to say,

563
00:27:22,737 --> 00:27:25,490
I think this is a keeper.

564
00:27:25,490 --> 00:27:26,960
I think this thing is here to say.

565
00:27:26,960 --> 00:27:29,900
Right now, two key
internet related issues

566
00:27:29,900 --> 00:27:31,610
are making the rounds in Washington DC.

567
00:27:31,610 --> 00:27:34,190
One involves the Net
Neutrality Act, which

568
00:27:34,190 --> 00:27:36,830
would allow larger, more powerful
corporations higher speed

569
00:27:36,830 --> 00:27:40,833
access to customers, establishing
a two tiered hierarchy amongst--

570
00:27:40,833 --> 00:27:42,500
you know what, it's awfully complicated.

571
00:27:42,500 --> 00:27:45,920
Why don't I let an expert, say the head
of the Senate Commerce Committee, which

572
00:27:45,920 --> 00:27:48,950
regulates e-commerce, explain.

573
00:27:48,950 --> 00:27:52,280
- The internet is not something
that you just dump something on.

574
00:27:52,280 --> 00:27:53,330
It's not a big truck.

575
00:27:53,330 --> 00:27:54,920
It's a series of tubes.

576
00:27:54,920 --> 00:27:57,818


577
00:27:57,818 --> 00:28:01,199
[APPLAUSE]

578
00:28:01,199 --> 00:28:05,080


579
00:28:05,080 --> 00:28:09,280
- All right, that might have sounded
more like something you'd hear from,

580
00:28:09,280 --> 00:28:13,135
let's say, a crazy old man
in an airport bar at 3:00 AM.

581
00:28:13,135 --> 00:28:15,770


582
00:28:15,770 --> 00:28:19,670
Then the chairman of the
Senate Commerce Committee.

583
00:28:19,670 --> 00:28:23,210
I'm sorry, sir, I don't quite think
I understand your dump truck tube

584
00:28:23,210 --> 00:28:25,040
symposium.

585
00:28:25,040 --> 00:28:27,560
Do you have something a
little more practical for me?

586
00:28:27,560 --> 00:28:30,080
- And if don't understand
those tubes can be filled,

587
00:28:30,080 --> 00:28:33,260
and if they're filled, when you put
your message in, it gets in line,

588
00:28:33,260 --> 00:28:35,990
it's going to be delayed by
anyone who puts in that tube

589
00:28:35,990 --> 00:28:39,873
enormous amounts of material,
enormous amounts of material.

590
00:28:39,873 --> 00:28:41,165
- And there you have it, folks.

591
00:28:41,165 --> 00:28:49,740
There's apparently-- there's apparently
an enormous amount of material clogging

592
00:28:49,740 --> 00:28:52,790
Ted Stevens tubes.

593
00:28:52,790 --> 00:28:58,010
Perhaps a little fiber optic
cable might be the answer.

594
00:28:58,010 --> 00:29:02,150
Stevens ended his lecture by
offering a concrete example

595
00:29:02,150 --> 00:29:04,800
of the problem we face.

596
00:29:04,800 --> 00:29:08,160
- Ten movies streaming
across the internet, and what

597
00:29:08,160 --> 00:29:10,890
happens to your own personal internet?

598
00:29:10,890 --> 00:29:14,720
I-- just the other day got internet
was set by my staff at 10 o'clock

599
00:29:14,720 --> 00:29:17,740
in morning on Friday,
I got it yesterday.

600
00:29:17,740 --> 00:29:18,240
Why?

601
00:29:18,240 --> 00:29:21,710


602
00:29:21,710 --> 00:29:26,280
- I'll tell you why, because the
creek run dry is what happened.

603
00:29:26,280 --> 00:29:28,740
And there's Comanches
in the [INAUDIBLE]..

604
00:29:28,740 --> 00:29:31,470
And the women of the internet.

605
00:29:31,470 --> 00:29:34,310
Actually, why didn't Senator
Stevens get it until yesterday?

606
00:29:34,310 --> 00:29:36,310
Well, this is just a
little bit of a guess here,

607
00:29:36,310 --> 00:29:39,660
but maybe it's because you
don't seem to know jack

608
00:29:39,660 --> 00:29:42,120
about computers or the internet.

609
00:29:42,120 --> 00:29:44,070
That's OK, that's OK.

610
00:29:44,070 --> 00:29:51,737
You're just the guy in
charge of regulating it.

611
00:29:51,737 --> 00:29:52,320
[END PLAYBACK]

612
00:29:52,320 --> 00:29:54,870
DAVID MALAN: So the
segue there is if you

613
00:29:54,870 --> 00:29:58,200
are feeling that you don't know jack
about computers and the internet,

614
00:29:58,200 --> 00:30:01,620
there's clearly people out there
who know just a little bit less.

615
00:30:01,620 --> 00:30:05,580
And we make this promise now that
we will not publicly lambast you

616
00:30:05,580 --> 00:30:08,520
as John did to Ted Stevens there.

617
00:30:08,520 --> 00:30:11,470
In fact, where are people really
coming from who take this course?

618
00:30:11,470 --> 00:30:15,360
So almost half of the students
who took this course last year

619
00:30:15,360 --> 00:30:18,660
had no prior programming
experience, 43%.

620
00:30:18,660 --> 00:30:20,830
About the same number
had a little experience,

621
00:30:20,830 --> 00:30:23,860
whether it was a programming
class or having tinkered or not.

622
00:30:23,860 --> 00:30:27,450
And then there was only 10% of the
class who had, quote unquote, a lot.

623
00:30:27,450 --> 00:30:29,970
Who maybe took not only
AP computer science,

624
00:30:29,970 --> 00:30:34,620
but maybe taught AP computer science,
or simply was certainly among even those

625
00:30:34,620 --> 00:30:37,860
I sort of made fun of
back in high school.

626
00:30:37,860 --> 00:30:40,840
This, though, there's
one other data point

627
00:30:40,840 --> 00:30:42,520
we'd like to share as well, so gender.

628
00:30:42,520 --> 00:30:45,900
So these were the numbers--

629
00:30:45,900 --> 00:30:47,520
well, it's funny.

630
00:30:47,520 --> 00:30:50,190
So these were the numbers last
year, and I would actually

631
00:30:50,190 --> 00:30:53,970
put forth that these are actually higher
than they have been in years past.

632
00:30:53,970 --> 00:30:57,480
And long story short, I don't know why
there's this discrepancy, because it's

633
00:30:57,480 --> 00:30:59,700
certainly not something
that has just arisen,

634
00:30:59,700 --> 00:31:02,677
but it's sort of been with computer
science departments for some time.

635
00:31:02,677 --> 00:31:05,760
We chatted with former female students
in the course, some of the teaching

636
00:31:05,760 --> 00:31:09,690
fellows, and there's certainly perhaps
some societal trends at play here.

637
00:31:09,690 --> 00:31:12,870
I think it's probably fair to say
that it's not the case that guys

638
00:31:12,870 --> 00:31:17,460
are better at computer
science, we've heard arguments

639
00:31:17,460 --> 00:31:18,900
like that put forth before.

640
00:31:18,900 --> 00:31:21,090
So I don't know, but I can
say that we, as a course,

641
00:31:21,090 --> 00:31:24,420
will at least try to do our part
to at least take a bigger bite out

642
00:31:24,420 --> 00:31:26,820
of the larger slice
there to see if we can't

643
00:31:26,820 --> 00:31:28,680
try to equalize these numbers somewhat.

644
00:31:28,680 --> 00:31:31,380
So whether you're male or
female, know, incidentally,

645
00:31:31,380 --> 00:31:33,885
that this Monday, today, and
this afternoon, this Wednesday

646
00:31:33,885 --> 00:31:37,010
and Thursday, we're going to be having
some of these very casual, should I,

647
00:31:37,010 --> 00:31:37,600
sessions.

648
00:31:37,600 --> 00:31:41,550
So if you ultimately exit this
course later this afternoon thinking,

649
00:31:41,550 --> 00:31:43,710
I'm still not sure if this
is for me, I'm still not

650
00:31:43,710 --> 00:31:46,210
sure if I can fit this in, or
really whatever your questions

651
00:31:46,210 --> 00:31:49,140
are concerns are, the teaching fellows
will be holding some casual Q&A

652
00:31:49,140 --> 00:31:51,510
sessions at these particular times.

653
00:31:51,510 --> 00:31:55,140
And you can, of course, if you're
feeling a little uncomfortable even

654
00:31:55,140 --> 00:31:57,300
beyond those, you can
send me an internet

655
00:31:57,300 --> 00:32:00,250
and we can talk more one-on-one.

656
00:32:00,250 --> 00:32:03,060
So let's see if we can't now begin
to level the playing field, just

657
00:32:03,060 --> 00:32:03,602
a little bit.

658
00:32:03,602 --> 00:32:06,480
Even if you don't know jack
about computers and the internet,

659
00:32:06,480 --> 00:32:10,260
you probably at least heard that the
basic building blocks that run them are

660
00:32:10,260 --> 00:32:13,960
bits, are the binary
system, are zeros and one's.

661
00:32:13,960 --> 00:32:16,060
So what does this mean and who cares?

662
00:32:16,060 --> 00:32:17,350
Why is this useful?

663
00:32:17,350 --> 00:32:20,010
Well, the easiest way to think
about these basic building

664
00:32:20,010 --> 00:32:23,910
blocks of computers is like
little light bulbs or little state

665
00:32:23,910 --> 00:32:25,680
machines that can either be on or off.

666
00:32:25,680 --> 00:32:28,350
Here, for instance, is an off
light bulb, back in the day,

667
00:32:28,350 --> 00:32:30,360
when it was easier to
turn the room's lights off

668
00:32:30,360 --> 00:32:32,910
we would just turn the lights off and
say zero, turn the lights on and say

669
00:32:32,910 --> 00:32:33,568
one.

670
00:32:33,568 --> 00:32:35,610
Doesn't really work well
in this particular room,

671
00:32:35,610 --> 00:32:38,310
so assume that this is our
light bulb representing zero,

672
00:32:38,310 --> 00:32:40,830
this is a light bulb that's
on, representing a one.

673
00:32:40,830 --> 00:32:43,950
Zero, one, off, on.

674
00:32:43,950 --> 00:32:46,200
So if you now have this
ability to distinguish

675
00:32:46,200 --> 00:32:49,275
between two states, so to
speak, the something that's on,

676
00:32:49,275 --> 00:32:51,900
something that's off, which
certainly you can implement clearly

677
00:32:51,900 --> 00:32:54,180
with electricity, just by
using something as simple

678
00:32:54,180 --> 00:32:57,533
as a light bulb or tinier like
a transistor or a capacitor,

679
00:32:57,533 --> 00:32:59,700
if you're familiar with
such terms, you can actually

680
00:32:59,700 --> 00:33:01,930
use these as basic building blocks.

681
00:33:01,930 --> 00:33:05,700
So how can you actually
use just zeros and ones

682
00:33:05,700 --> 00:33:08,970
to do everything that that computer
is capable of, whether it's

683
00:33:08,970 --> 00:33:11,250
sending instant messages,
whether it's sending emails,

684
00:33:11,250 --> 00:33:12,870
whether it's browsing the web.

685
00:33:12,870 --> 00:33:17,080
Everything inside of this machine, this
machine, the cell phones in your pocket

686
00:33:17,080 --> 00:33:19,770
these days boil down to zeros and ones.

687
00:33:19,770 --> 00:33:23,160
Well, how can you possibly
represent such arbitrary information

688
00:33:23,160 --> 00:33:26,370
using such simple bits of information?

689
00:33:26,370 --> 00:33:30,000
Well, think back for a moment,
if you will, to grade school.

690
00:33:30,000 --> 00:33:36,840
So this number here 123 in
the so-called decimal system.

691
00:33:36,840 --> 00:33:37,890
Pretty straightforward.

692
00:33:37,890 --> 00:33:41,100
All right, so why does that
represent the number 123?

693
00:33:41,100 --> 00:33:45,630
Well, if I recall, I was taught that
this is what's called the ones column,

694
00:33:45,630 --> 00:33:49,892
this is the tens column, and
this is the one hundreds column.

695
00:33:49,892 --> 00:33:50,850
Pretty straightforward.

696
00:33:50,850 --> 00:33:53,460
Why is this the number we know as 123?

697
00:33:53,460 --> 00:33:58,770
Well, that's because we have three
ones, so three times one, plus two tens.

698
00:33:58,770 --> 00:34:05,010
So that's plus two times 10, that's
23, plus one hundred, So one times 100.

699
00:34:05,010 --> 00:34:07,770
And OK, didn't really get very
far with that, but that gives me

700
00:34:07,770 --> 00:34:09,719
what I know to be the number one.

701
00:34:09,719 --> 00:34:11,610
But there was actually a process there.

702
00:34:11,610 --> 00:34:15,330
Each of these digits, so to
speak, from zero through nine

703
00:34:15,330 --> 00:34:18,840
took on different significance based
on the column that they were in.

704
00:34:18,840 --> 00:34:22,389
Well, binary, the system the computers
use, is really the same thing.

705
00:34:22,389 --> 00:34:26,460
So up here, I've pre-populated the
slide with different placeholders,

706
00:34:26,460 --> 00:34:29,190
different column values, because
in the world of computers

707
00:34:29,190 --> 00:34:33,060
and the world of binary, where your
only digits are not zero through nine

708
00:34:33,060 --> 00:34:37,120
but just zero through one, is you just
treat the columns a little differently.

709
00:34:37,120 --> 00:34:39,000
So the right one is
still the ones column,

710
00:34:39,000 --> 00:34:43,170
but the next one over is not the
tens column but the twos column.

711
00:34:43,170 --> 00:34:46,530
To the left of that the fours,
the eights, the sixteens.

712
00:34:46,530 --> 00:34:48,690
So the pattern
fundamentally is the same.

713
00:34:48,690 --> 00:34:50,580
These seem to be powers of 10.

714
00:34:50,580 --> 00:34:53,830
10 to the zero, 10 to
the one, 10 to the two.

715
00:34:53,830 --> 00:34:59,550
Here we have two to the zero, two to
the one, two to the two, and so forth.

716
00:34:59,550 --> 00:35:00,370
But that's all.

717
00:35:00,370 --> 00:35:03,260
Everything boils down
to the same system.

718
00:35:03,260 --> 00:35:07,300
So for instance, if we have eight bits
or eight light bulbs arranged in a row,

719
00:35:07,300 --> 00:35:10,960
just because it's useful to
think of bits as being in a clump

720
00:35:10,960 --> 00:35:15,280
so that we can count higher than one,
this set of eight off light bulbs

721
00:35:15,280 --> 00:35:18,040
obviously represents the number zero.

722
00:35:18,040 --> 00:35:18,970
Not all that hard.

723
00:35:18,970 --> 00:35:21,910
This row here, instead,
with the right most one on,

724
00:35:21,910 --> 00:35:24,247
that bit is a one, because
the light bulb is on.

725
00:35:24,247 --> 00:35:26,080
Well, that thing just
represents-- all right

726
00:35:26,080 --> 00:35:29,090
we've got a one in the one column,
so that's one times one is one.

727
00:35:29,090 --> 00:35:30,400
But what about the next row?

728
00:35:30,400 --> 00:35:34,210
Well, this represents two, because
one of the bits is turned on,

729
00:35:34,210 --> 00:35:37,030
is flipped, so to speak, to
be a one in the twos column.

730
00:35:37,030 --> 00:35:38,710
This is going to be three.

731
00:35:38,710 --> 00:35:40,090
And then what's the pattern here?

732
00:35:40,090 --> 00:35:43,900
If there were another
row, how do I get to four?

733
00:35:43,900 --> 00:35:47,350
Well, you flip one more up,
you carry the one, so to speak,

734
00:35:47,350 --> 00:35:50,650
and then the other two guys become off.

735
00:35:50,650 --> 00:35:53,810
All right, well what about
a little exercise here?

736
00:35:53,810 --> 00:35:56,800
So this is what the same thing--
just replacing the light bulbs

737
00:35:56,800 --> 00:35:58,390
with explicit zeros and ones.

738
00:35:58,390 --> 00:35:59,140
How about this.

739
00:35:59,140 --> 00:36:02,700
So you are in what zip
code right now, freshman?

740
00:36:02,700 --> 00:36:04,260
02138.

741
00:36:04,260 --> 00:36:09,390
So on a piece of scrap paper, in your
head, or not at all, what would--

742
00:36:09,390 --> 00:36:16,880
how would we go about encoding
02138 in this particular example?

743
00:36:16,880 --> 00:36:19,340
All zeros, I heard, excellent.

744
00:36:19,340 --> 00:36:20,630
What about the next one?

745
00:36:20,630 --> 00:36:24,120


746
00:36:24,120 --> 00:36:27,460
OK, so I'll give you 10
seconds of an at home exercise.

747
00:36:27,460 --> 00:36:30,990
And if you're finding this a little
too easy, skip ahead to, oh, the eight,

748
00:36:30,990 --> 00:36:33,988
do the last one.

749
00:36:33,988 --> 00:36:37,030
So you're going to be putting on each
of these dashed lines, in your head

750
00:36:37,030 --> 00:36:39,960
or on a piece of paper,
the value of zero or one.

751
00:36:39,960 --> 00:36:46,190


752
00:36:46,190 --> 00:36:50,178
02138.

753
00:36:50,178 --> 00:36:52,270
All right, not so hard.

754
00:36:52,270 --> 00:36:53,080
OK, so that's it.

755
00:36:53,080 --> 00:36:53,580
02138.

756
00:36:53,580 --> 00:36:56,850
Now realize, we're talking about
bits for the most part here.

757
00:36:56,850 --> 00:37:00,660
You're more used, probably, to talking
about bytes and kilobytes and megabytes

758
00:37:00,660 --> 00:37:02,680
and gigabytes and now terabytes.

759
00:37:02,680 --> 00:37:05,850
Well, a byte is just eight bits.

760
00:37:05,850 --> 00:37:09,672
And a kilobyte is just
1,000 bytes and so forth,

761
00:37:09,672 --> 00:37:11,380
and we'll revisit
these kinds of numbers,

762
00:37:11,380 --> 00:37:15,070
particularly later in the semester when
we start talking about data and such.

763
00:37:15,070 --> 00:37:17,760
Now I thought I'd give you
a little comic strip that

764
00:37:17,760 --> 00:37:19,320
was actually printed in a newspaper.

765
00:37:19,320 --> 00:37:25,580
If you chuckle at this,
you belong in CS50.

766
00:37:25,580 --> 00:37:28,370
So now you understand a little bit.

767
00:37:28,370 --> 00:37:30,650
Wow, this did not go over
funny at all this year.

768
00:37:30,650 --> 00:37:34,070
Everyone last year thought
this was hilarious.

769
00:37:34,070 --> 00:37:36,350
If you're not quite sure
what it means, maybe you

770
00:37:36,350 --> 00:37:40,130
should ask the person more
comfortable to your right or left.

771
00:37:40,130 --> 00:37:41,870
So who cares about zeros and ones?

772
00:37:41,870 --> 00:37:45,170
Who cares about the fact that we can
represent numbers greater than one

773
00:37:45,170 --> 00:37:47,840
using multiple zeros and ones?

774
00:37:47,840 --> 00:37:49,650
Well, this is intentionally scary.

775
00:37:49,650 --> 00:37:51,620
This is what's called the ASCII table.

776
00:37:51,620 --> 00:37:54,140
So way back when, some people
decided, you know what?

777
00:37:54,140 --> 00:37:57,350
So that computers are useful
and not just calculators,

778
00:37:57,350 --> 00:38:01,080
but can actually display alphabetic
information, symbolic information

779
00:38:01,080 --> 00:38:04,970
and the like, why don't we use
longer sequences of zeros and ones,

780
00:38:04,970 --> 00:38:10,140
like entire bytes, for instance, and map
them to say, letters of the alphabet.

781
00:38:10,140 --> 00:38:14,247
So if you look down the middle
column or the third column here,

782
00:38:14,247 --> 00:38:15,830
you'll see this is the decimal column.

783
00:38:15,830 --> 00:38:18,247
You can pretty much ignore
most of the other columns here.

784
00:38:18,247 --> 00:38:22,790
But notice that the decimal number 65,
some years ago, was semi-arbitrarily

785
00:38:22,790 --> 00:38:27,170
decided to henceforth represent
capital A. Which is to say,

786
00:38:27,170 --> 00:38:29,840
if a computer ever
encounters on its hard drive

787
00:38:29,840 --> 00:38:33,200
or in RAM a sequence of
eight bits that, when

788
00:38:33,200 --> 00:38:35,810
you do all the math with the
placeholders and whatnot,

789
00:38:35,810 --> 00:38:40,490
gives you the number 65, what that
means is the computer should display not

790
00:38:40,490 --> 00:38:44,480
the value 65 in that context,
but the letter A. And thus

791
00:38:44,480 --> 00:38:47,330
was born the concept of word
processing and the ability

792
00:38:47,330 --> 00:38:50,570
to actually communicate in
English and other languages.

793
00:38:50,570 --> 00:38:54,890
If we fast forward to 97, that was
decided to represent lowercase A.

794
00:38:54,890 --> 00:38:57,200
And you'll certainly--
no computer scientists

795
00:38:57,200 --> 00:39:00,290
would memorize say, this entire chart,
but turns out with just those two,

796
00:39:00,290 --> 00:39:03,590
you can kind of bootstrap yourself
and figure out many of the other ones.

797
00:39:03,590 --> 00:39:07,040
But fortunately, computers
generally do that for us.

798
00:39:07,040 --> 00:39:11,210
Well, if you have the ability to count
in binary, represent larger numbers,

799
00:39:11,210 --> 00:39:14,955
in turn, represent letters
of the alphabet, well,

800
00:39:14,955 --> 00:39:16,580
how do you actually store these things?

801
00:39:16,580 --> 00:39:20,750
Because certainly, our computers don't
have millions of light bulbs, per se.

802
00:39:20,750 --> 00:39:24,390
So what I thought I would
do is take a video here,

803
00:39:24,390 --> 00:39:26,660
which is a little cheesy
with its voiceover,

804
00:39:26,660 --> 00:39:29,485
but nonetheless, gives an interesting
view inside of a hard drive.

805
00:39:29,485 --> 00:39:30,152
[VIDEO PLAYBACK]

806
00:39:30,152 --> 00:39:33,930
- The hard drive is where your PC
stores most of its permanent data.

807
00:39:33,930 --> 00:39:36,980
To do that, the data
travels from RAM along

808
00:39:36,980 --> 00:39:41,300
with software signals that tell the
hard drive how to store that data.

809
00:39:41,300 --> 00:39:46,230
The hard drive circuits translate those
signals into voltage fluctuations.

810
00:39:46,230 --> 00:39:49,400
These, in turn, control the
hard drives moving parts.

811
00:39:49,400 --> 00:39:53,100
Some of the few moving parts
left in the modern computer.

812
00:39:53,100 --> 00:39:57,440
Some of the signals control a motor
which spins metal coded platters.

813
00:39:57,440 --> 00:40:00,710
Their data is actually
stored on these platters.

814
00:40:00,710 --> 00:40:05,930
Other signals move the read write heads,
to read or write data on the platters.

815
00:40:05,930 --> 00:40:09,980
This machinery is so precise
that a human hair couldn't even

816
00:40:09,980 --> 00:40:12,440
pass between the heads
and spinning platters.

817
00:40:12,440 --> 00:40:15,157
Yet, it all works at terrific speeds.

818
00:40:15,157 --> 00:40:15,740
[END PLAYBACK]

819
00:40:15,740 --> 00:40:20,473
DAVID MALAN: And part two of
that goes a little bit deeper.

820
00:40:20,473 --> 00:40:21,140
[VIDEO PLAYBACK]

821
00:40:21,140 --> 00:40:23,960
- Let's look at what we
just saw in slow motion.

822
00:40:23,960 --> 00:40:27,470
When a brief pulse of electricity
is sent to the read/write head,

823
00:40:27,470 --> 00:40:31,280
it flips on a tiny electromagnet
for a fraction of a second.

824
00:40:31,280 --> 00:40:34,490
The magnet creates a field
which changes the polarity

825
00:40:34,490 --> 00:40:37,010
of a tiny, tiny portion
of the metal particles

826
00:40:37,010 --> 00:40:39,350
which coat each platter surface.

827
00:40:39,350 --> 00:40:42,380
A pattern series of these tiny
charged up areas on the disk

828
00:40:42,380 --> 00:40:47,010
represents a single bit of data in the
binary number system used by computers.

829
00:40:47,010 --> 00:40:49,790
Now, if the current is sent one
way through the read/write head,

830
00:40:49,790 --> 00:40:52,308
the area's polarized in one direction.

831
00:40:52,308 --> 00:40:54,350
If the current is sent in
the opposite direction,

832
00:40:54,350 --> 00:40:56,450
the polarization is reversed.

833
00:40:56,450 --> 00:40:58,790
How do you get data off the hard disk?

834
00:40:58,790 --> 00:41:00,630
Just reverse the process.

835
00:41:00,630 --> 00:41:02,900
So it's the particles on the
disk that get the current

836
00:41:02,900 --> 00:41:04,640
in the read/write head moving.

837
00:41:04,640 --> 00:41:08,540
Put together millions of this magnetized
segments, and you've got a file.

838
00:41:08,540 --> 00:41:13,340
Now the pieces of a single file may be
scattered all over drive's platters,

839
00:41:13,340 --> 00:41:16,630
kind of like the mess
of papers on your desk.

840
00:41:16,630 --> 00:41:19,950
So a special extra file keeps
track of where everything is.

841
00:41:19,950 --> 00:41:23,567
Don't you wish you had
something like that?

842
00:41:23,567 --> 00:41:24,150
[END PLAYBACK]

843
00:41:24,150 --> 00:41:27,120
DAVID MALAN: It's so educational
up until that last part.

844
00:41:27,120 --> 00:41:28,650
I did come prepared, incidentally.

845
00:41:28,650 --> 00:41:30,990
If you were a little
unnerved by all this talk

846
00:41:30,990 --> 00:41:33,110
of low-level magnetic
particles, I did bring this.

847
00:41:33,110 --> 00:41:35,964
I don't think we really need it though.

848
00:41:35,964 --> 00:41:36,840
[VIDEO PLAYBACK]

849
00:41:36,840 --> 00:41:40,140
- This is the on/off switch.

850
00:41:40,140 --> 00:41:42,410
[END PLAYBACK]

851
00:41:42,410 --> 00:41:44,160
DAVID MALAN: So what's
the takeaway there?

852
00:41:44,160 --> 00:41:46,860
Well, inside of hard drives,
there are these metal platters.

853
00:41:46,860 --> 00:41:49,250
On those metal platters
are magnetic particles,

854
00:41:49,250 --> 00:41:51,750
and those particles, essentially,
can be arranged say North,

855
00:41:51,750 --> 00:41:55,650
South, representing a one, or
South, North, representing a zero.

856
00:41:55,650 --> 00:41:58,110
And out of those basic
physical building blocks

857
00:41:58,110 --> 00:42:02,070
can you begin to represent those logical
entities, those conceptual entities

858
00:42:02,070 --> 00:42:04,350
like zeros and ones and bits.

859
00:42:04,350 --> 00:42:06,150
So enough on that for now.

860
00:42:06,150 --> 00:42:07,800
What is CS50?

861
00:42:07,800 --> 00:42:11,230
The course catalog description
kind of scares with a bit of terms.

862
00:42:11,230 --> 00:42:12,600
What does this actually mean?

863
00:42:12,600 --> 00:42:15,600
Well, the course's expectations are
to attend all lectures and sections,

864
00:42:15,600 --> 00:42:19,620
complete nine problem sets, take two
quizzes, and produce the final project.

865
00:42:19,620 --> 00:42:21,720
There is no final exam in this course.

866
00:42:21,720 --> 00:42:23,640
How are grades computed?

867
00:42:23,640 --> 00:42:27,450
Most of the grade in this course is
weighted toward the problem sets,

868
00:42:27,450 --> 00:42:30,640
because that is by far where you
will spend most of your time.

869
00:42:30,640 --> 00:42:34,470
We are all quite familiar with the idea
of either bombing a problem set or just

870
00:42:34,470 --> 00:42:36,370
being a bad week or
something to that effect.

871
00:42:36,370 --> 00:42:38,412
So know that you will be
able to drop your lowest

872
00:42:38,412 --> 00:42:41,130
score on one of these problem
sets at the end of the semester

873
00:42:41,130 --> 00:42:42,300
when your grade is computed.

874
00:42:42,300 --> 00:42:45,060
The quizzes and the final
project are weighted as follows,

875
00:42:45,060 --> 00:42:46,920
and you may take this course pass, fail.

876
00:42:46,920 --> 00:42:49,320
Look to the courses FAQ
section in the syllabus

877
00:42:49,320 --> 00:42:51,270
for a little discussion on this.

878
00:42:51,270 --> 00:42:53,220
Realize that this is--

879
00:42:53,220 --> 00:42:56,020
the TFs can confirm or
deny this more one-on-one,

880
00:42:56,020 --> 00:43:00,930
this course is not so much hard,
I think, as it is time consuming.

881
00:43:00,930 --> 00:43:03,450
And that was the case
when I took the course,

882
00:43:03,450 --> 00:43:05,670
and I do think that's
the case these days,

883
00:43:05,670 --> 00:43:08,520
but more on that in just a little bit.

884
00:43:08,520 --> 00:43:10,890
The course's website is at cs50.net.

885
00:43:10,890 --> 00:43:12,958
More on that as time
passes, since there's

886
00:43:12,958 --> 00:43:15,000
a particularly interesting
architecture as you'll

887
00:43:15,000 --> 00:43:16,590
see underlying that this year.

888
00:43:16,590 --> 00:43:18,750
Cloud computing will
be the buzz word there.

889
00:43:18,750 --> 00:43:19,660
What about books?

890
00:43:19,660 --> 00:43:22,600
So there are no required
books for this course.

891
00:43:22,600 --> 00:43:25,320
You will get plenty of information,
we assure you, from lectures,

892
00:43:25,320 --> 00:43:27,610
sections, the internet, and so forth.

893
00:43:27,610 --> 00:43:29,640
However, if you are
the type of student who

894
00:43:29,640 --> 00:43:32,850
likes the comfort of a book, who
needs to have a book in order to take

895
00:43:32,850 --> 00:43:35,070
a class, we do recommend a few books.

896
00:43:35,070 --> 00:43:37,960
And we recommend them along two
different tracks, so to speak.

897
00:43:37,960 --> 00:43:41,820
So those of you who are a little
uncomfortable or very uncomfortable

898
00:43:41,820 --> 00:43:44,880
with the mere idea that you're
in this core shopping it today,

899
00:43:44,880 --> 00:43:47,280
if you decide to take
it and want to start

900
00:43:47,280 --> 00:43:49,830
the course with a bit of
hand-holding and textual form,

901
00:43:49,830 --> 00:43:52,552
know that this is the
book that we recommend.

902
00:43:52,552 --> 00:43:55,260
There is no shame in buying a book
called The Absolute Beginner's

903
00:43:55,260 --> 00:43:58,530
Guide to C, just realize that this
book is not really a reference book.

904
00:43:58,530 --> 00:44:02,160
You'll chew it up,
learn it, and then that

905
00:44:02,160 --> 00:44:04,110
will be it for that particular book.

906
00:44:04,110 --> 00:44:07,590
But it's very good for gaining
a bit of comfort early on.

907
00:44:07,590 --> 00:44:10,140
For those more comfortable,
so to speak, this

908
00:44:10,140 --> 00:44:11,940
is the sort of book
that risks putting you

909
00:44:11,940 --> 00:44:14,100
to sleep if you try to read
it from cover to cover,

910
00:44:14,100 --> 00:44:15,855
but it's a wonderful reference.

911
00:44:15,855 --> 00:44:17,730
And it's not really the
type of book that you

912
00:44:17,730 --> 00:44:20,910
would curl up in bed with and read
from cover to cover, but rather,

913
00:44:20,910 --> 00:44:23,430
turn to the chapter, turn to
the index for whatever topic

914
00:44:23,430 --> 00:44:25,530
is of particular interest to you there.

915
00:44:25,530 --> 00:44:30,510
Do you realize that free,
if not superior resources do

916
00:44:30,510 --> 00:44:34,740
exist on the interwebs, and we link
to those on the course's website

917
00:44:34,740 --> 00:44:35,700
under Resources.

918
00:44:35,700 --> 00:44:37,560
For everyone, we recommend this book.

919
00:44:37,560 --> 00:44:40,320
This is a wonderfully fun
book that goes more into depth

920
00:44:40,320 --> 00:44:42,360
on things like those
videos we just showed.

921
00:44:42,360 --> 00:44:45,540
How does a hard drive work, how
does an iPhone work, and things

922
00:44:45,540 --> 00:44:48,990
like this, which are rather tangential
to the ultimate goals of the course,

923
00:44:48,990 --> 00:44:52,260
but are nonetheless
interesting and certainly

924
00:44:52,260 --> 00:44:55,350
help take the fear factor, or
at least the unfamiliarity,

925
00:44:55,350 --> 00:44:58,650
around some of the toys that
we ourselves carry every day.

926
00:44:58,650 --> 00:45:02,180
And for that 10% or
even fewer of you who

927
00:45:02,180 --> 00:45:05,910
were the true hacker-minded
types in this course who

928
00:45:05,910 --> 00:45:09,960
care about shaving milliseconds off
of the running time of your code,

929
00:45:09,960 --> 00:45:12,880
know that this is actually a
really valuable reference book.

930
00:45:12,880 --> 00:45:15,480
And for those types, frankly,
a good curl up in bed

931
00:45:15,480 --> 00:45:17,460
cover to cover kind of read.

932
00:45:17,460 --> 00:45:20,970
I use this myself in grad
school to optimize some research

933
00:45:20,970 --> 00:45:24,660
code that I wrote, and it's a
wonderfully valuable, geeky type book

934
00:45:24,660 --> 00:45:25,240
to have.

935
00:45:25,240 --> 00:45:27,810
So those are at the Coop, but
don't tell them I said this,

936
00:45:27,810 --> 00:45:30,600
you'll find them much cheaper
online, at say amazon.com, which

937
00:45:30,600 --> 00:45:32,820
is where the course website links.

938
00:45:32,820 --> 00:45:38,920
So Coops not here, though we are,
of course, on two cameras here.

939
00:45:38,920 --> 00:45:41,460
So speaking of cameras.

940
00:45:41,460 --> 00:45:44,340
So this course will take place here.

941
00:45:44,340 --> 00:45:47,190
It is, however, filmed for students
who either can't make a class

942
00:45:47,190 --> 00:45:49,440
or who want to review some class.

943
00:45:49,440 --> 00:45:52,560
Know that in addition to the
courses lectures and these videos,

944
00:45:52,560 --> 00:45:55,980
one of the teaching fellows will also
take scribe notes during each lecture

945
00:45:55,980 --> 00:45:59,280
and then those will be posted online
within a few days, too, not only

946
00:45:59,280 --> 00:46:01,590
as a valuable reference when
it comes time for quizzes

947
00:46:01,590 --> 00:46:03,960
or if you want to fast
forward to certain parts

948
00:46:03,960 --> 00:46:06,630
or maybe slow down certain parts
during which I was confusing,

949
00:46:06,630 --> 00:46:08,255
or fast forward through certain parts--

950
00:46:08,255 --> 00:46:13,800


951
00:46:13,800 --> 00:46:17,040
--take place on Mondays and
Wednesdays, no lectures on Fridays.

952
00:46:17,040 --> 00:46:18,690
But what we thought we'd do during--

953
00:46:18,690 --> 00:46:24,770


954
00:46:24,770 --> 00:46:27,320
--suggested in some
Q-guide like forms that we

955
00:46:27,320 --> 00:46:29,540
have tea with David once a week.

956
00:46:29,540 --> 00:46:31,850
I don't really do tea,
but I'll do lunch.

957
00:46:31,850 --> 00:46:34,880
So what we thought we would do--
and we'll see if anyone comes--

958
00:46:34,880 --> 00:46:38,420
is at least I would plant myself in one
of the dining halls or the faculty club

959
00:46:38,420 --> 00:46:41,540
or somewhere on campus on Fridays,
during what would otherwise

960
00:46:41,540 --> 00:46:45,200
be class time, to just do sort of
casual office hours, grab a bite,

961
00:46:45,200 --> 00:46:49,760
and see if we can't get a few people
to come spend lunch time with me,

962
00:46:49,760 --> 00:46:52,400
just so we know who to expect
so that we can plan accordingly.

963
00:46:52,400 --> 00:46:54,410
If you ever do take us
up on such an offer,

964
00:46:54,410 --> 00:46:56,980
email that address there just
so we know who to expect.

965
00:46:56,980 --> 00:47:00,260
It's not so much that we think we're
going to be overloaded with requests

966
00:47:00,260 --> 00:47:02,930
of people wanting to eat lunch with me.

967
00:47:02,930 --> 00:47:04,170
So what about this thing?

968
00:47:04,170 --> 00:47:08,360
So we are very technically
minded people here.

969
00:47:08,360 --> 00:47:11,960
And so last year, we started
podcasting the course.

970
00:47:11,960 --> 00:47:14,630
And what that means is these
videos are available online

971
00:47:14,630 --> 00:47:18,770
in QuickTime format, MP3 format,
as well as in Flash format.

972
00:47:18,770 --> 00:47:25,940
If you are particularly inclined, you
can pull up, God forbid, me, on your--

973
00:47:25,940 --> 00:47:28,068
is that good?

974
00:47:28,068 --> 00:47:29,360
I still get a kick out of that.

975
00:47:29,360 --> 00:47:33,350
But I don't know who would want
to watch a computer science

976
00:47:33,350 --> 00:47:36,410
course on an iPod or an iPhone,
or at least admit to it.

977
00:47:36,410 --> 00:47:40,730
I, frankly, if you can
see, actually, lest

978
00:47:40,730 --> 00:47:44,490
you think that I am
completely out there.

979
00:47:44,490 --> 00:47:47,690
So that's what I have on mine, here.

980
00:47:47,690 --> 00:47:49,820
Besides that one video of me.

981
00:47:49,820 --> 00:47:51,680
But know that that is possible.

982
00:47:51,680 --> 00:47:53,900
More interesting than
that, though, perhaps is

983
00:47:53,900 --> 00:47:56,630
the fact that one, CS50 for
the first time this year

984
00:47:56,630 --> 00:47:59,000
will also be offered through
Harvard's Extension School

985
00:47:59,000 --> 00:48:01,698
to students who want to enroll,
partake in the course remotely,

986
00:48:01,698 --> 00:48:03,740
via the internet, wherever
they are in the world,

987
00:48:03,740 --> 00:48:05,780
and receive credit through
the Extension School.

988
00:48:05,780 --> 00:48:08,720
Because the course is
podcasted, we also had

989
00:48:08,720 --> 00:48:11,630
random people on the interwebs
tuning into the course.

990
00:48:11,630 --> 00:48:14,600
And we're going to take things
one step further this year,

991
00:48:14,600 --> 00:48:19,187
really in an effort to give something
back, so to speak, to those out there.

992
00:48:19,187 --> 00:48:21,770
In addition to the course being
filmed and all of the handouts

993
00:48:21,770 --> 00:48:24,370
and all of the problems that's
being made available online,

994
00:48:24,370 --> 00:48:26,870
we're going to try to take
things one step further this year

995
00:48:26,870 --> 00:48:31,110
and use technology to further package
up a course like this and its content

996
00:48:31,110 --> 00:48:34,280
for really, anyone who wants to turn
in and bootstrap themselves out there,

997
00:48:34,280 --> 00:48:38,030
who might not have the fortune, frankly,
of sitting down in a room like this.

998
00:48:38,030 --> 00:48:42,650
And we will make use of things called
virtual machines, whereby long story

999
00:48:42,650 --> 00:48:44,460
short, more on this
later in the semester,

1000
00:48:44,460 --> 00:48:48,530
we will create images of computers
that people-- anyone out there--

1001
00:48:48,530 --> 00:48:52,560
can download onto their own Macs, PCs,
Linux boxes, double click an icon.

1002
00:48:52,560 --> 00:48:56,450
And what they will get inside of their
own Macintosh or inside of their own PC

1003
00:48:56,450 --> 00:49:01,340
is a window inside of which is our
own copy of, say Windows or Linux

1004
00:49:01,340 --> 00:49:04,460
or whatever operating system we
decide to deploy so that they really

1005
00:49:04,460 --> 00:49:07,748
have their own sandbox environment
with which to engage in the class.

1006
00:49:07,748 --> 00:49:10,040
And we will also make such
images available to students

1007
00:49:10,040 --> 00:49:13,580
in the course, who, even
though we provide cs50.net

1008
00:49:13,580 --> 00:49:15,350
as a course-wide computing structure.

1009
00:49:15,350 --> 00:49:18,860
If you are particularly
geeky and so inclined,

1010
00:49:18,860 --> 00:49:21,860
you'll be able to really test out
these fairly nascent technologies

1011
00:49:21,860 --> 00:49:25,760
on your own systems as well and
administer your own Linux machine,

1012
00:49:25,760 --> 00:49:28,880
for instance, within your own Mac or PC.

1013
00:49:28,880 --> 00:49:30,050
So what about sections?

1014
00:49:30,050 --> 00:49:32,180
So sections and the
course's teaching fellows

1015
00:49:32,180 --> 00:49:34,010
are an integral part
of the core sections,

1016
00:49:34,010 --> 00:49:36,890
will supplement the courses
lectures and dive into more depth

1017
00:49:36,890 --> 00:49:38,122
on problem sets and material.

1018
00:49:38,122 --> 00:49:39,830
For the first time
this year, we're going

1019
00:49:39,830 --> 00:49:43,280
to borrow an idea from
[INAUDIBLE],, which

1020
00:49:43,280 --> 00:49:45,800
is another class that meets in
here, and that's about music,

1021
00:49:45,800 --> 00:49:48,830
and it too has a range
of students' backgrounds.

1022
00:49:48,830 --> 00:49:51,500
The A sections, the B
sections, and the C sections.

1023
00:49:51,500 --> 00:49:54,620
When I took that course
years ago, I was in A or C,

1024
00:49:54,620 --> 00:49:57,592
whatever the people who don't
know much about music were in.

1025
00:49:57,592 --> 00:50:00,800
We're going to borrow that same idea,
and we're not going to use A, B, and C,

1026
00:50:00,800 --> 00:50:04,068
but describe them as sections for
those more, those less comfortable,

1027
00:50:04,068 --> 00:50:05,360
and those somewhere in between.

1028
00:50:05,360 --> 00:50:07,790
And we'll take care of
sectioning this Wednesday

1029
00:50:07,790 --> 00:50:10,460
or thereafter, more
on that as time comes.

1030
00:50:10,460 --> 00:50:12,830
The goal for these
multiple tracks is one,

1031
00:50:12,830 --> 00:50:15,800
we can handle it now, given that
the course is sufficiently large.

1032
00:50:15,800 --> 00:50:20,420
And two, it's to provide not only the
more comfortable people with a forum,

1033
00:50:20,420 --> 00:50:23,570
an environment where they can really
ask those questions that might scare

1034
00:50:23,570 --> 00:50:26,362
the hell out of the less comfortable
students sometime, or at least

1035
00:50:26,362 --> 00:50:29,310
annoy the less comfortable, even
students somewhere in between,

1036
00:50:29,310 --> 00:50:32,300
but can further stimulate
themselves by being

1037
00:50:32,300 --> 00:50:34,070
in a room full of
other people who really

1038
00:50:34,070 --> 00:50:36,710
want to get their hands dirty
with some technical minutia,

1039
00:50:36,710 --> 00:50:39,200
led by a teaching fellow
who's just as, if not more

1040
00:50:39,200 --> 00:50:40,700
comfortable with that kind of stuff.

1041
00:50:40,700 --> 00:50:42,700
And on the other hand,
we'll have other sections

1042
00:50:42,700 --> 00:50:45,140
that cater also to the
comfort levels of students

1043
00:50:45,140 --> 00:50:48,140
who just don't have that
background or that level of comfort

1044
00:50:48,140 --> 00:50:49,700
with that material.

1045
00:50:49,700 --> 00:50:51,810
So more on that later this week.

1046
00:50:51,810 --> 00:50:53,630
So the course's staff.

1047
00:50:53,630 --> 00:51:01,670
So this course's staff is perhaps bigger
than the average class size at Harvard.

1048
00:51:01,670 --> 00:51:05,720
So we have over 50 people involved
in the day-to-day operation

1049
00:51:05,720 --> 00:51:07,250
of this course.

1050
00:51:07,250 --> 00:51:10,440
Some of them are sitting here today
who aren't shopping their own classes--

1051
00:51:10,440 --> 00:51:13,670
can the courses teaching fellows
who are here stand up for a moment?

1052
00:51:13,670 --> 00:51:15,830
We're mostly grouped here.

1053
00:51:15,830 --> 00:51:16,804
Oh, wow.

1054
00:51:16,804 --> 00:51:20,052
[APPLAUSE]

1055
00:51:20,052 --> 00:51:21,910


1056
00:51:21,910 --> 00:51:26,320
So these are just a few of the
faces that you will never forget.

1057
00:51:26,320 --> 00:51:29,710
[INAUDIBLE],, in 1996, was my
teaching fellow, thank you guys.

1058
00:51:29,710 --> 00:51:33,460
And I have never forgot the day
that sitting in the back right hand

1059
00:51:33,460 --> 00:51:36,910
corner of Elliott Dining Hall,
he was taking time out of his day

1060
00:51:36,910 --> 00:51:40,930
to deal with me, who still didn't
get these things called pointers.

1061
00:51:40,930 --> 00:51:43,870
But that was the day where
things finally clicked for me.

1062
00:51:43,870 --> 00:51:47,080
And this is absolutely the
course that long after lectures

1063
00:51:47,080 --> 00:51:50,710
are over and long after, daresay,
you've graduated from Harvard,

1064
00:51:50,710 --> 00:51:53,740
will you remember your teaching
fellow in this, and perhaps

1065
00:51:53,740 --> 00:51:56,140
a few other, courses as well.

1066
00:51:56,140 --> 00:51:58,953
[INAUDIBLE] is the course's
head teaching fellow

1067
00:51:58,953 --> 00:52:01,370
and will be helping with the
administration of the course,

1068
00:52:01,370 --> 00:52:02,703
a lot of the sectioning details.

1069
00:52:02,703 --> 00:52:04,630
And so she is a face that--

1070
00:52:04,630 --> 00:52:08,032
[APPLAUSE]

1071
00:52:08,032 --> 00:52:11,440


1072
00:52:11,440 --> 00:52:13,992
Many of you, I'm sure, will
become well familiar with,

1073
00:52:13,992 --> 00:52:17,200
over time-- do know that in addition to
myself and the other teaching fellows

1074
00:52:17,200 --> 00:52:20,252
and course assistants and anyone
involved in the courses production,

1075
00:52:20,252 --> 00:52:22,960
know that you can turn to any of
us, in particularly, [INAUDIBLE]

1076
00:52:22,960 --> 00:52:25,370
for questions you have,
for concerns that you have,

1077
00:52:25,370 --> 00:52:27,190
particularly even this first week.

1078
00:52:27,190 --> 00:52:30,370
I think she'll be the first to admit
that she was certainly, at one point,

1079
00:52:30,370 --> 00:52:32,410
among those of you less comfortable.

1080
00:52:32,410 --> 00:52:35,230
And so if you're feeling a bit of
apprehension along those lines,

1081
00:52:35,230 --> 00:52:39,010
by all means, strike up a
conversation with any of us.

1082
00:52:39,010 --> 00:52:41,230
So what else exists
in the way of support?

1083
00:52:41,230 --> 00:52:44,230
This is perhaps the most beautiful
you will ever see the Science Center.

1084
00:52:44,230 --> 00:52:48,760
So if you look at this photo online, the
skies are bluer than they've ever been,

1085
00:52:48,760 --> 00:52:49,818
the grass is greener.

1086
00:52:49,818 --> 00:52:53,110
And you will spend time in the basement
of this building for this course, where

1087
00:52:53,110 --> 00:52:55,900
we have dozens of
computers that students

1088
00:52:55,900 --> 00:53:00,340
log into for one-on-one assistance
with the courses problem sets

1089
00:53:00,340 --> 00:53:01,690
in the form of office hours.

1090
00:53:01,690 --> 00:53:04,480
More on that once we get
to problem set one, really.

1091
00:53:04,480 --> 00:53:07,390
But we also introduced last year
virtual office hours, whereby

1092
00:53:07,390 --> 00:53:09,670
you can log into the
course's website, pull up

1093
00:53:09,670 --> 00:53:13,030
some platform independent Java-based
software called Illuminate.

1094
00:53:13,030 --> 00:53:15,820
Log into what's really a glorified
chat room, but one in which

1095
00:53:15,820 --> 00:53:18,400
you can click an icon to
raise your hand, so to speak.

1096
00:53:18,400 --> 00:53:20,920
A little icon will flash on
the teaching fellows screen.

1097
00:53:20,920 --> 00:53:24,010
And we can then, not only chat
with you via this instant messaging

1098
00:53:24,010 --> 00:53:27,530
window on the bottom left corner,
but also see what's on your screen,

1099
00:53:27,530 --> 00:53:30,160
and even, if you let us,
take control of your screen

1100
00:53:30,160 --> 00:53:33,400
and help you troubleshoot whatever
bug is hanging you up at that time,

1101
00:53:33,400 --> 00:53:36,950
whether you are at brain break in
your dorm room or even off campus.

1102
00:53:36,950 --> 00:53:38,450
So we'll be using those as well.

1103
00:53:38,450 --> 00:53:40,670
So what do we expect in return?

1104
00:53:40,670 --> 00:53:42,950
So this is the course's workload.

1105
00:53:42,950 --> 00:53:46,120
This is the kind of
course that you learn--

1106
00:53:46,120 --> 00:53:50,560
it's the sort of material
that you learn only by doing.

1107
00:53:50,560 --> 00:53:52,990
In the course's lectures,
I try to present

1108
00:53:52,990 --> 00:53:54,910
a mental framework for
the week, introduce

1109
00:53:54,910 --> 00:53:58,900
concepts that give you a sense of
what the course's content is about.

1110
00:53:58,900 --> 00:54:02,710
In sections, we'll elaborate on that,
go into additional examples and details.

1111
00:54:02,710 --> 00:54:05,050
But it's truly in the
course's problem sets

1112
00:54:05,050 --> 00:54:07,677
where you will take the
most away from this course.

1113
00:54:07,677 --> 00:54:10,510
And even though, to some of you,
particularly freshmen, might think,

1114
00:54:10,510 --> 00:54:14,440
my god, five to 10 hours
per week on a class?

1115
00:54:14,440 --> 00:54:15,670
There are other extremes.

1116
00:54:15,670 --> 00:54:19,040
So computer science 161 years
ago, when I was a senior,

1117
00:54:19,040 --> 00:54:21,580
I took, it was like 40 hours a week.

1118
00:54:21,580 --> 00:54:25,000
Now that's not representative of all
of the computer science courses here,

1119
00:54:25,000 --> 00:54:27,820
but it at least makes this
look like a walk in the park.

1120
00:54:27,820 --> 00:54:31,690
But the upside is-- and you can look
to the courses syllabus and website

1121
00:54:31,690 --> 00:54:33,190
and even to past teaching--

1122
00:54:33,190 --> 00:54:35,470
current and past teaching
fellows and students,

1123
00:54:35,470 --> 00:54:37,580
we like to think they're a lot of fun.

1124
00:54:37,580 --> 00:54:39,670
We'll give you a quick
survey of them today.

1125
00:54:39,670 --> 00:54:42,640
But this is absolutely the
type of the course where

1126
00:54:42,640 --> 00:54:46,330
if you do loan us some portion
of your life for the semester,

1127
00:54:46,330 --> 00:54:49,600
we're pretty comfortable promising
that you will not only get it back,

1128
00:54:49,600 --> 00:54:52,210
eventually, but also a lot more.

1129
00:54:52,210 --> 00:54:53,980
So more on that as time proceeds.

1130
00:54:53,980 --> 00:54:56,650
What, then, will we be
doing in this course?

1131
00:54:56,650 --> 00:54:58,990
Well, in the first week
and including today,

1132
00:54:58,990 --> 00:55:00,460
we'll bite off some of the basics.

1133
00:55:00,460 --> 00:55:05,530
And the course will start
in a fairly friendly way.

1134
00:55:05,530 --> 00:55:08,170
Oh, this is an example of
this interwebs technology.

1135
00:55:08,170 --> 00:55:11,140
Hi world is what we'll use this
year instead of hello world--

1136
00:55:11,140 --> 00:55:12,625
more on that to come.

1137
00:55:12,625 --> 00:55:14,690
What we'll use in the
course's first week,

1138
00:55:14,690 --> 00:55:17,140
namely Wednesday, is
introducing programming itself,

1139
00:55:17,140 --> 00:55:19,480
by a way of a really
interesting programming

1140
00:55:19,480 --> 00:55:23,650
environment that was developed a
couple of years ago by MIT'S Media Lab.

1141
00:55:23,650 --> 00:55:28,450
So we will very quickly next week dive
into the C programming language, where

1142
00:55:28,450 --> 00:55:30,070
we will spend much of the semester.

1143
00:55:30,070 --> 00:55:34,330
But just to set the stage, I thought I'd
pull up this programming environment,

1144
00:55:34,330 --> 00:55:36,700
which literally allows
you to program things

1145
00:55:36,700 --> 00:55:40,000
by dragging and dropping puzzle
pieces that lock together,

1146
00:55:40,000 --> 00:55:42,310
if that makes logical sense.

1147
00:55:42,310 --> 00:55:44,892
This is not what programming,
ultimately, tends to be about,

1148
00:55:44,892 --> 00:55:47,350
because clearly, this is not
the most sophisticated program

1149
00:55:47,350 --> 00:55:48,340
that one might make.

1150
00:55:48,340 --> 00:55:51,970
But what it allows us-- what it allows
you to do in the course's first week,

1151
00:55:51,970 --> 00:55:55,510
frankly, is one, hopefully have a
bit of fun with actual programming,

1152
00:55:55,510 --> 00:55:57,310
albeit in a playful context.

1153
00:55:57,310 --> 00:56:01,060
But two, also give you a sense,
frankly, of gratification.

1154
00:56:01,060 --> 00:56:05,680
It's very hard to impress people by
typing a command at a blinking cursor

1155
00:56:05,680 --> 00:56:08,980
and then getting back some
hello world kind of response.

1156
00:56:08,980 --> 00:56:14,514
Much more interesting is, for
instance, something like this.

1157
00:56:14,514 --> 00:56:15,181
[VIDEO PLAYBACK]

1158
00:56:15,181 --> 00:56:18,590
[MUSIC PLAYING]

1159
00:56:18,590 --> 00:56:29,697


1160
00:56:29,697 --> 00:56:30,280
[END PLAYBACK]

1161
00:56:30,280 --> 00:56:33,820
OK, much more interesting for some
definition of much more interesting.

1162
00:56:33,820 --> 00:56:34,750
That's all it does.

1163
00:56:34,750 --> 00:56:36,790
I will say, the music
and the flashing lights,

1164
00:56:36,790 --> 00:56:39,290
frankly, if you watch it late
at night, gets kind of trippy.

1165
00:56:39,290 --> 00:56:42,310
So you might want to pull that one up.

1166
00:56:42,310 --> 00:56:48,550
Let me pull up one that wasn't made
by a student who then distributed

1167
00:56:48,550 --> 00:56:52,630
the software with Scratch, but rather,
pull up this, which one of our courses

1168
00:56:52,630 --> 00:56:55,420
teaching fellows, now
CAs, Andrew Berry, one

1169
00:56:55,420 --> 00:56:58,660
of Harvard's football stars, actually,
made during our staff training

1170
00:56:58,660 --> 00:56:59,818
last year.

1171
00:56:59,818 --> 00:57:02,110
I love all of the teaching
fellows, equally, of course,

1172
00:57:02,110 --> 00:57:04,550
but this is kind of my favorite.

1173
00:57:04,550 --> 00:57:08,624
So let's take a look at what Andrew did.

1174
00:57:08,624 --> 00:57:12,103
[MUSIC - THE WEATHER GIRLS, "IT'S
 RAINING MEN"]

1175
00:57:12,103 --> 00:57:37,338


1176
00:57:37,338 --> 00:57:37,880
(SINGING) Hi.

1177
00:57:37,880 --> 00:57:38,380
Hi.

1178
00:57:38,380 --> 00:57:39,785
We're your weather girls.

1179
00:57:39,785 --> 00:57:42,810
And have we got news for you.

1180
00:57:42,810 --> 00:57:44,010
You better listen.

1181
00:57:44,010 --> 00:57:48,826
Get ready, all you lonely girls
and leave those umbrella's at home.

1182
00:57:48,826 --> 00:57:50,824
All right.

1183
00:57:50,824 --> 00:57:51,788
Humidity's rising.

1184
00:57:51,788 --> 00:57:54,680


1185
00:57:54,680 --> 00:57:56,608
Barometer's getting low.

1186
00:57:56,608 --> 00:57:58,550
How low, girl?

1187
00:57:58,550 --> 00:57:59,688
According to all sources.

1188
00:57:59,688 --> 00:58:01,520
What sources now?

1189
00:58:01,520 --> 00:58:03,287
The street's the place to go.

1190
00:58:03,287 --> 00:58:05,042
We better hurry up.

1191
00:58:05,042 --> 00:58:11,592
'Cause tonight for the first
time just about half past ten.

1192
00:58:11,592 --> 00:58:19,400
For the first time in history
it's gonna start raining men.

1193
00:58:19,400 --> 00:58:21,329
It's raining men.

1194
00:58:21,329 --> 00:58:25,161
Hallelujah it's raining men.

1195
00:58:25,161 --> 00:58:27,080
Amen.

1196
00:58:27,080 --> 00:58:28,155
I'm going to go--

1197
00:58:28,155 --> 00:58:30,530
DAVID MALAN: So we'll make
that available on the course's

1198
00:58:30,530 --> 00:58:32,511
website for you if you'd like.

1199
00:58:32,511 --> 00:58:35,878
[APPLAUSE]

1200
00:58:35,878 --> 00:58:37,330


1201
00:58:37,330 --> 00:58:39,670
Let me ask, at the
risk of putting you in,

1202
00:58:39,670 --> 00:58:44,350
what's by nature, a little uncomfortable
for one volunteer, to join me up here.

1203
00:58:44,350 --> 00:58:45,700
I need one volunteer.

1204
00:58:45,700 --> 00:58:47,140
Yes, come on down.

1205
00:58:47,140 --> 00:58:49,240
What is your name?

1206
00:58:49,240 --> 00:58:50,050
Greg, OK.

1207
00:58:50,050 --> 00:58:51,820
Greg is going to join me
up here for just a moment.

1208
00:58:51,820 --> 00:58:53,110
Greg, you have to be
comfortable before you

1209
00:58:53,110 --> 00:58:56,020
walk in front of two video
cameras and the entire internet,

1210
00:58:56,020 --> 00:58:57,760
being on the internet.

1211
00:58:57,760 --> 00:59:02,200
And we'll need you to sign a piece
of paper from the lawyers after this.

1212
00:59:02,200 --> 00:59:03,320
But come on up.

1213
00:59:03,320 --> 00:59:05,750
So not only with this
programming environment

1214
00:59:05,750 --> 00:59:08,950
can you create these
animations, these interactions,

1215
00:59:08,950 --> 00:59:12,512
you can also take user input and
actually create interactive games.

1216
00:59:12,512 --> 00:59:14,470
So for instance, this
was made by [INAUDIBLE],,

1217
00:59:14,470 --> 00:59:18,880
one of our students, now CAs this
year, or now virtual teaching fellows.

1218
00:59:18,880 --> 00:59:20,560
The rules are fairly straightforward.

1219
00:59:20,560 --> 00:59:23,570
This is Scratch Scratch
Revolution, similar, of course,

1220
00:59:23,570 --> 00:59:25,060
to DDR, if you're familiar.

1221
00:59:25,060 --> 00:59:28,210
You're simply going to use the
left, right, down, and up arrows,

1222
00:59:28,210 --> 00:59:30,160
so that as things are
flowing on the screen,

1223
00:59:30,160 --> 00:59:33,850
you want to hit the key exactly as the
colored arrow is lined up on the top.

1224
00:59:33,850 --> 00:59:34,630
Makes sense?

1225
00:59:34,630 --> 00:59:35,200
All right.

1226
00:59:35,200 --> 00:59:35,855
All yours.

1227
00:59:35,855 --> 00:59:36,730
Let's see how you do.

1228
00:59:36,730 --> 00:59:38,063
[MUSIC - KANYE WEST, "STRONGER"]

1229
00:59:38,063 --> 00:59:42,490
(SINGING) Work it, make it, do it, makes
us, harder, better, faster, stronger.

1230
00:59:42,490 --> 00:59:45,908
Now that, that don't kill me,
can only make me stronger,

1231
00:59:45,908 --> 00:59:50,600
I need you to hurry up now,
because I can't wait much longer.

1232
00:59:50,600 --> 00:59:56,124
I know I got to be right now, 'cause
I can't wait much longer, man, I've

1233
00:59:56,124 --> 00:59:59,666
been waiting all night, now,
that's how long I've been on you.

1234
00:59:59,666 --> 01:00:04,620
You know how long I've been on
you, since Prince was on Apollonia,

1235
01:00:04,620 --> 01:00:09,000
since OJ had Isotoners, don't
act like I never told you.

1236
01:00:09,000 --> 01:00:13,588
You know how long I've been on
you, since Prince was on Apollonia,

1237
01:00:13,588 --> 01:00:18,503
since OJ had Isotoners, don't
act like I never told you.

1238
01:00:18,503 --> 01:00:20,400
Told you, never told you.

1239
01:00:20,400 --> 01:00:23,080
Told you, never told you.

1240
01:00:23,080 --> 01:00:24,860
Told you, told you, never told you.

1241
01:00:24,860 --> 01:00:27,590
Told you, told you, never told.

1242
01:00:27,590 --> 01:00:31,280
DAVID MALAN: How about
a big hand for Greg?

1243
01:00:31,280 --> 01:00:31,940
Thank you.

1244
01:00:31,940 --> 01:00:36,730


1245
01:00:36,730 --> 01:00:39,632
So we'll make that one available
on the course's website as well.

1246
01:00:39,632 --> 01:00:42,340
And so that's how we'll spend not
only this Wednesday in lecture,

1247
01:00:42,340 --> 01:00:44,350
presenting some of the
interesting concepts that

1248
01:00:44,350 --> 01:00:45,980
arise as a result of that.

1249
01:00:45,980 --> 01:00:48,160
But also, to set the
stage for problem set

1250
01:00:48,160 --> 01:00:50,830
zero, which this semester
will similarly task you

1251
01:00:50,830 --> 01:00:53,320
with really taking that
environment out for a spin

1252
01:00:53,320 --> 01:00:55,450
and doing something that
is of interest to you.

1253
01:00:55,450 --> 01:00:58,720
In fact, for what we'll call a hacker
edition, more on that in a moment,

1254
01:00:58,720 --> 01:01:02,080
we will also make available these
little circuit boards which have sensors

1255
01:01:02,080 --> 01:01:05,950
built into them like this little slider,
little sockets for alligator clips,

1256
01:01:05,950 --> 01:01:10,150
a button here, it's got a
microphone as well, as well as

1257
01:01:10,150 --> 01:01:11,795
a couple of light sensor, too.

1258
01:01:11,795 --> 01:01:14,920
So that you can actually integrate not
only human input with, say, fingers,

1259
01:01:14,920 --> 01:01:17,330
but also environmental input as well.

1260
01:01:17,330 --> 01:01:20,650
So we'll be curious to see what
those hackers among you do with that.

1261
01:01:20,650 --> 01:01:24,400
The week after will be very rapidly
dive into C. This programming

1262
01:01:24,400 --> 01:01:27,370
language called C, where we'll
spend much of the semester exploring

1263
01:01:27,370 --> 01:01:30,850
the fundamentals of computer
science, and in turn, programming.

1264
01:01:30,850 --> 01:01:33,040
In week two, we will
continue that discussion,

1265
01:01:33,040 --> 01:01:36,400
but also talk about some real-world
applications of the same,

1266
01:01:36,400 --> 01:01:39,820
focusing particularly on cryptography.

1267
01:01:39,820 --> 01:01:43,150
Focusing in week three,
then, we will look at--

1268
01:01:43,150 --> 01:01:46,390
and week three will we then
focus on some of those ideas

1269
01:01:46,390 --> 01:01:49,090
that I hinted at before,
things involving phone books

1270
01:01:49,090 --> 01:01:51,580
and counting millions
or billions of students,

1271
01:01:51,580 --> 01:01:53,470
searching and sorting,
and actually trying

1272
01:01:53,470 --> 01:01:57,100
to get a sense of just how
good or bad your program is

1273
01:01:57,100 --> 01:02:01,750
based on its running time, given
some increasingly large inputs.

1274
01:02:01,750 --> 01:02:04,120
In week four, we'll
look at data structures,

1275
01:02:04,120 --> 01:02:07,300
clever ways of
implementing programs that

1276
01:02:07,300 --> 01:02:11,410
need to store more than just
numbers and say, words in memory.

1277
01:02:11,410 --> 01:02:14,560
We'll also talk about some low-level
details like memory management.

1278
01:02:14,560 --> 01:02:17,650
How a computer actually moves
those zeros and ones around,

1279
01:02:17,650 --> 01:02:21,110
and what risks your computer
is at when you, the programmer,

1280
01:02:21,110 --> 01:02:24,050
don't move those zeros and
ones around very safely.

1281
01:02:24,050 --> 01:02:28,270
Many of the so-called hacks or
compromises of websites and servers

1282
01:02:28,270 --> 01:02:32,410
these days often boil down, still today,
to what are called buffer overflow

1283
01:02:32,410 --> 01:02:37,510
exploits, which relate directly to
the world's popular use of C, C++,

1284
01:02:37,510 --> 01:02:40,480
and similar language, that
puts you at risk, albeit,

1285
01:02:40,480 --> 01:02:45,190
giving you at the same time more power
over your program of hackers actually

1286
01:02:45,190 --> 01:02:46,390
getting into your system.

1287
01:02:46,390 --> 01:02:50,200
Well, in week five, we'll introduce
another element of realism.

1288
01:02:50,200 --> 01:02:54,100
I spent summer a few years ago interning
for the district attorney's office

1289
01:02:54,100 --> 01:02:57,880
in Middlesex County, where quite
literally, the local police would

1290
01:02:57,880 --> 01:03:02,380
bring in hard drives and memory sticks,
and sometimes monitors and mice.

1291
01:03:02,380 --> 01:03:06,460
But we would then look at
the data on those machines

1292
01:03:06,460 --> 01:03:09,770
and try to provide the prosecutors
with whatever tidbit of information

1293
01:03:09,770 --> 01:03:11,800
it was they were looking for.

1294
01:03:11,800 --> 01:03:16,660
Truth be told, sometimes forensics is
not as sexy as it seems to be on TV.

1295
01:03:16,660 --> 01:03:19,120
Sometimes we literally double
clicked on My Documents,

1296
01:03:19,120 --> 01:03:22,420
and there was the evidence.

1297
01:03:22,420 --> 01:03:24,070
We, though, will dive a bit deeper.

1298
01:03:24,070 --> 01:03:27,070
In fact, this is an excerpt from one
of the problem sets from the course

1299
01:03:27,070 --> 01:03:28,280
last year.

1300
01:03:28,280 --> 01:03:33,070
This was an image we made and
embedded a secret murder mystery in.

1301
01:03:33,070 --> 01:03:35,440
If you think back to
childhood, and if you're

1302
01:03:35,440 --> 01:03:38,710
kind of doing that thing
where you focus your eyes,

1303
01:03:38,710 --> 01:03:42,160
trying to stare through the projector
screen, it's not that thing at all.

1304
01:03:42,160 --> 01:03:46,150
So it's actually the thing where
you get like that red piece

1305
01:03:46,150 --> 01:03:49,150
of cellophane plastic
in like a cereal box,

1306
01:03:49,150 --> 01:03:52,480
and then if you hold the piece of red
plastic over some otherwise red piece

1307
01:03:52,480 --> 01:03:54,040
of paper, a message pops through.

1308
01:03:54,040 --> 01:03:58,962
Well, we gave everyone a graphical
image, a digital image like this,

1309
01:03:58,962 --> 01:04:00,670
and they then had to
write a program that

1310
01:04:00,670 --> 01:04:03,610
simulated that red piece
of plastic, so as to reveal

1311
01:04:03,610 --> 01:04:05,320
who it was that had done it.

1312
01:04:05,320 --> 01:04:07,600
And I think last year,
it was Colonel Mustard

1313
01:04:07,600 --> 01:04:09,640
in the study with the candlestick.

1314
01:04:09,640 --> 01:04:11,548
So that was the solution
to that problem.

1315
01:04:11,548 --> 01:04:14,590
In week six, we'll return our focus
to data structures, talk about things

1316
01:04:14,590 --> 01:04:17,230
called linked lists and
techniques with which

1317
01:04:17,230 --> 01:04:20,710
you can solve increasingly
sophisticated and interesting problems.

1318
01:04:20,710 --> 01:04:23,140
We'll look in week seven at
things called hash tables

1319
01:04:23,140 --> 01:04:25,720
and binary search trees,
compression algorithms,

1320
01:04:25,720 --> 01:04:27,790
heaps and tries, as they're called.

1321
01:04:27,790 --> 01:04:31,330
In week eight, then, we'll be
transition away from our world

1322
01:04:31,330 --> 01:04:34,900
and focus on C into
one that is web-based,

1323
01:04:34,900 --> 01:04:37,877
where the web is clearly
increasingly the place to be

1324
01:04:37,877 --> 01:04:39,460
when it comes to software development.

1325
01:04:39,460 --> 01:04:42,880
Google, for instance, has been a pioneer
in terms of buying or implementing

1326
01:04:42,880 --> 01:04:44,860
things like Google
Docs and spreadsheets,

1327
01:04:44,860 --> 01:04:47,360
and even Microsoft has begun
to take those same initiatives.

1328
01:04:47,360 --> 01:04:50,830
So if you don't know it already, we
will teach you how to make web pages.

1329
01:04:50,830 --> 01:04:55,420
XHTML, HTML, we'll teach you a
little bit about HTTP and TCP/IP,

1330
01:04:55,420 --> 01:04:57,310
things you've probably
heard about, but maybe

1331
01:04:57,310 --> 01:04:59,140
have not gotten your hands dirty with.

1332
01:04:59,140 --> 01:05:04,360
We'll introduce at that point PHP, and
a database query language called SQL.

1333
01:05:04,360 --> 01:05:07,540
With these languages will we be
able to transition the problem

1334
01:05:07,540 --> 01:05:12,080
sets from an interesting and powerful,
but command-line environment,

1335
01:05:12,080 --> 01:05:15,730
so to speak, to one that is browser
based, and spend a couple of problems

1336
01:05:15,730 --> 01:05:16,480
sets there.

1337
01:05:16,480 --> 01:05:20,080
In fact, in week nine,
will we introduced

1338
01:05:20,080 --> 01:05:22,660
the notion or the
context of mashups, which

1339
01:05:22,660 --> 01:05:25,930
is this increasingly popular
phenomenon whereby people make

1340
01:05:25,930 --> 01:05:29,230
available different types
of programming code online,

1341
01:05:29,230 --> 01:05:32,380
different data sets, Google being
one of them, Yahoo and the like,

1342
01:05:32,380 --> 01:05:36,160
and you can take all these different
data sets and all these different code

1343
01:05:36,160 --> 01:05:39,700
that other people have written
and mash them up together

1344
01:05:39,700 --> 01:05:41,680
to do yet more interesting things.

1345
01:05:41,680 --> 01:05:45,370
A canonical one in the world
of mashups is taking Craigslist

1346
01:05:45,370 --> 01:05:48,100
and taking Google Maps
and actually overlaying

1347
01:05:48,100 --> 01:05:50,140
markers on Google Maps
wherever there are

1348
01:05:50,140 --> 01:05:52,300
apartments that are available for rent.

1349
01:05:52,300 --> 01:05:55,810
But things are increasingly
sophisticated these days.

1350
01:05:55,810 --> 01:05:59,230
Some of you might be
familiar with Google Earth.

1351
01:05:59,230 --> 01:06:02,260
So Google Earth is this
wonderfully fun tool

1352
01:06:02,260 --> 01:06:04,660
that I was actually
introduced to a few years ago

1353
01:06:04,660 --> 01:06:07,570
when I was just auditing
an archeology course here.

1354
01:06:07,570 --> 01:06:10,660
We can, for instance, go to
one Oxford Street in 02138,

1355
01:06:10,660 --> 01:06:13,720
which is roughly where we are,
it's the Science Center's address.

1356
01:06:13,720 --> 01:06:15,730
If you've never played
with this program before,

1357
01:06:15,730 --> 01:06:18,272
I urge you to spend the next
one or two days playing with it,

1358
01:06:18,272 --> 01:06:22,030
just because you can literally take
virtual vacations in your dorm room.

1359
01:06:22,030 --> 01:06:25,390
Here we are hovering
over the Science Center.

1360
01:06:25,390 --> 01:06:30,550
Using the controls here, we can
zoom in, we can re-angle ourselves,

1361
01:06:30,550 --> 01:06:32,942
we can see some interesting
3D topologies there.

1362
01:06:32,942 --> 01:06:34,900
There's a link to this
on the course's website.

1363
01:06:34,900 --> 01:06:37,790
But what Google recently
introduced, for instance,

1364
01:06:37,790 --> 01:06:41,200
is not only their Google Maps
API, with which I did things

1365
01:06:41,200 --> 01:06:46,540
like Shuttle Boy and the GPS setup,
but they also introduced a plug-in

1366
01:06:46,540 --> 01:06:48,820
for web browsers for Google Earth.

1367
01:06:48,820 --> 01:06:51,610
And one of the things I
thought would be fun to show

1368
01:06:51,610 --> 01:06:54,460
is something that we
may end up playing with,

1369
01:06:54,460 --> 01:06:57,760
this notion of using
Google Earth's plugin--

1370
01:06:57,760 --> 01:07:01,120
which I wonder if this
is going to work here.

1371
01:07:01,120 --> 01:07:03,310
Oh, had such good momentum there.

1372
01:07:03,310 --> 01:07:08,130
Let's see if we can do it in
IE, if it's going to work.

1373
01:07:08,130 --> 01:07:10,130
OK, no.

1374
01:07:10,130 --> 01:07:10,630
All right.

1375
01:07:10,630 --> 01:07:13,380
We're going to run this in the
background and we're going to-- oh,

1376
01:07:13,380 --> 01:07:16,310
so close to having every
demo actually work correctly.

1377
01:07:16,310 --> 01:07:19,150
So we might end up playing with
one or more of Google's APIs

1378
01:07:19,150 --> 01:07:20,230
is the takeaway there.

1379
01:07:20,230 --> 01:07:22,840
If you haven't already played
with something like this,

1380
01:07:22,840 --> 01:07:26,800
I urge you to play not only with Google
Earth, or this slowly downloading

1381
01:07:26,800 --> 01:07:29,710
plug-in, but we'll also revisit
that later in the semester.

1382
01:07:29,710 --> 01:07:32,440
And near course's end will we
actually look a bit at hardware.

1383
01:07:32,440 --> 01:07:35,770
We will take for granted the fact that
there is some machine underneath it all

1384
01:07:35,770 --> 01:07:38,530
that's actually running our
code and in making possible

1385
01:07:38,530 --> 01:07:40,390
all the things that
we do and talk about,

1386
01:07:40,390 --> 01:07:44,200
what it means to compile your code
and what it means to be a CPU.

1387
01:07:44,200 --> 01:07:48,040
And in the course's second to last
week will we take things up a notch

1388
01:07:48,040 --> 01:07:50,020
and talk about enterprise architectures.

1389
01:07:50,020 --> 01:07:52,145
Talking about, well, what
do you need when you want

1390
01:07:52,145 --> 01:07:53,673
to go run, say, a tech-type startup.

1391
01:07:53,673 --> 01:07:56,590
What do you actually need to build,
what do you need to wire together,

1392
01:07:56,590 --> 01:07:57,790
what are your alternatives?

1393
01:07:57,790 --> 01:08:01,000
We'll talk in this week about
cloud computing and virtualization.

1394
01:08:01,000 --> 01:08:03,970
The idea that you don't need
to necessarily buy computers

1395
01:08:03,970 --> 01:08:07,840
anymore and connect them, you don't need
to buy hard drives and storage anymore.

1396
01:08:07,840 --> 01:08:11,200
You can rather pay someone
else a few cents on the dollar

1397
01:08:11,200 --> 01:08:15,550
and just rent computing cycles,
rent memory, rent space.

1398
01:08:15,550 --> 01:08:19,240
And in fact, that is what we'll be
doing with cs50.net this semester.

1399
01:08:19,240 --> 01:08:21,670
Rather than use Harvard's
own computing infrastructure,

1400
01:08:21,670 --> 01:08:27,580
we will literally pay Amazon about $0.10
an hour to use one of their super fancy

1401
01:08:27,580 --> 01:08:31,930
virtual machines and multiple such
instances that we will virtually wire

1402
01:08:31,930 --> 01:08:36,234
together and create for you all the
illusion of one computing cluster that

1403
01:08:36,234 --> 01:08:38,859
you can then connect to, to
actually work on your problem sets.

1404
01:08:38,859 --> 01:08:40,689
And the neat thing
about this approach is

1405
01:08:40,689 --> 01:08:44,740
that for problem sets that involve
a particularly lot of computation,

1406
01:08:44,740 --> 01:08:47,290
a lot of use of disk,
well, we just have to type

1407
01:08:47,290 --> 01:08:49,540
a few commands, double
the number of computers,

1408
01:08:49,540 --> 01:08:51,790
quote unquote, that are
actually in the cluster.

1409
01:08:51,790 --> 01:08:53,680
We can then handle that
load for that week,

1410
01:08:53,680 --> 01:08:56,013
and as soon as the problem
set's submitted, we turn off.

1411
01:08:56,013 --> 01:08:59,310
Those virtual machines, they're
no longer ours but available

1412
01:08:59,310 --> 01:09:00,310
for someone else to use.

1413
01:09:00,310 --> 01:09:02,628
And we'll of course, in week
12, conclude the course.

1414
01:09:02,628 --> 01:09:04,420
Well, what about the
course's problem sets,

1415
01:09:04,420 --> 01:09:08,229
where we'll spend most of
the outside of class time?

1416
01:09:08,229 --> 01:09:11,830
Well, problem set zero will be
released later this week on Wednesday.

1417
01:09:11,830 --> 01:09:15,370
Next week will we look
at C and problem set one.

1418
01:09:15,370 --> 01:09:16,090
Crypto.

1419
01:09:16,090 --> 01:09:18,819
In one of the problems
this year will you actually

1420
01:09:18,819 --> 01:09:24,340
try to crack passwords, so to speak,
where you will implement software

1421
01:09:24,340 --> 01:09:28,149
with which to decrypt and/or encrypt
information, sensitive information,

1422
01:09:28,149 --> 01:09:29,470
and see what gets revealed.

1423
01:09:29,470 --> 01:09:30,950
We'll look also at forensics.

1424
01:09:30,950 --> 01:09:33,670
So in addition to maybe doing
that red cellophane tape thing,

1425
01:09:33,670 --> 01:09:37,120
I will also, likely, like
last fall, take a stroll

1426
01:09:37,120 --> 01:09:38,920
throughout campus with
my digital camera,

1427
01:09:38,920 --> 01:09:42,160
snapping photos of some
interesting spots on campus

1428
01:09:42,160 --> 01:09:45,430
onto a normal digital-- like Canon
digital camera with a compact flash

1429
01:09:45,430 --> 01:09:45,979
card.

1430
01:09:45,979 --> 01:09:49,720
Unfortunately, I will likely
accidentally format that compact flash

1431
01:09:49,720 --> 01:09:51,310
card, like I did last fall.

1432
01:09:51,310 --> 01:09:54,850
I'll then make an image-- a forensic
image of that compact flash card,

1433
01:09:54,850 --> 01:09:57,880
post it, essentially, on the course's
website for you all to download,

1434
01:09:57,880 --> 01:10:00,700
and then write your own
forensic tool with which

1435
01:10:00,700 --> 01:10:05,620
to go recover all of the JPEGs, all
of the photographs, that for a noob,

1436
01:10:05,620 --> 01:10:08,500
so to speak, would otherwise
be completely lost.

1437
01:10:08,500 --> 01:10:11,740
We'll look in problems set six at the
idea of implementing not just a spell

1438
01:10:11,740 --> 01:10:15,190
checker, but the fastest
possible spell checker.

1439
01:10:15,190 --> 01:10:17,740
Even engaging in a bit of
competition, optionally,

1440
01:10:17,740 --> 01:10:20,080
with your peers, whereby
we'll benchmark your code,

1441
01:10:20,080 --> 01:10:22,010
post the results on
the course's website,

1442
01:10:22,010 --> 01:10:24,400
and see if we can't get
you to obsessively fine

1443
01:10:24,400 --> 01:10:28,000
tune your code, right up
until the time of submission.

1444
01:10:28,000 --> 01:10:31,690
Last year toward the end of the
semester, the course's final problem

1445
01:10:31,690 --> 01:10:35,080
set was to implement what we
called CS50 finance, which

1446
01:10:35,080 --> 01:10:38,860
was an e-trade like web-based program
with which students, once they

1447
01:10:38,860 --> 01:10:42,100
implemented it, could get
real-time stock quotes from Yahoo,

1448
01:10:42,100 --> 01:10:45,610
could be given 10,000 virtual
dollars in their portfolio

1449
01:10:45,610 --> 01:10:48,350
that they could then use
to buy stocks, sell stocks.

1450
01:10:48,350 --> 01:10:50,350
So it was an online
portfolio management tool,

1451
01:10:50,350 --> 01:10:52,267
so we'll likely do
something like that, again.

1452
01:10:52,267 --> 01:10:54,700
As well as in the last
problem set introduced

1453
01:10:54,700 --> 01:10:56,860
JavaScript and
object-oriented programming.

1454
01:10:56,860 --> 01:11:00,400
Likely the idea of mash-ups and
do something similar in spirit

1455
01:11:00,400 --> 01:11:02,920
to what Shuttle Boy, for instance, was.

1456
01:11:02,920 --> 01:11:06,920
But the climax of this course
is absolutely its final project.

1457
01:11:06,920 --> 01:11:09,070
So the final project
will be your opportunity

1458
01:11:09,070 --> 01:11:12,760
to take your newfound skills and
savvy with programming out for a spin

1459
01:11:12,760 --> 01:11:15,880
and actually make something
that's purely of interest

1460
01:11:15,880 --> 01:11:18,517
to you, subject to
just a few guidelines.

1461
01:11:18,517 --> 01:11:21,600
We'll encourage you, at that point,
to build something that interests you,

1462
01:11:21,600 --> 01:11:23,392
something that's actually
useful, something

1463
01:11:23,392 --> 01:11:26,710
that solves an actual problem, be it
for this course, for your research,

1464
01:11:26,710 --> 01:11:27,610
just for fun.

1465
01:11:27,610 --> 01:11:31,360
But ideally, somehow impact campus.

1466
01:11:31,360 --> 01:11:34,300
In fact, next year, as
most of you probably know,

1467
01:11:34,300 --> 01:11:38,200
the University is changing its
calendar, whereby it's a good thing.

1468
01:11:38,200 --> 01:11:40,210
Exams will come before
winter break, which

1469
01:11:40,210 --> 01:11:44,097
means there will no longer be this
month of either slacking or stressing,

1470
01:11:44,097 --> 01:11:46,180
depending on the type of
personality that you are.

1471
01:11:46,180 --> 01:11:48,620
But it does put a wrinkle
in the course's 10,

1472
01:11:48,620 --> 01:11:50,678
15 year tradition of
having a final project

1473
01:11:50,678 --> 01:11:53,470
in the course, because we tend to
use reading period, if not break,

1474
01:11:53,470 --> 01:11:58,190
to actually allow you this opportunity
to dive in to your own work of art.

1475
01:11:58,190 --> 01:12:01,750
So what we will do for the
first and maybe last time ever

1476
01:12:01,750 --> 01:12:05,830
is culminate the course in what
we're calling a the CS50 Fair.

1477
01:12:05,830 --> 01:12:09,820
Think back to middle school science
fair, but not so cheesy with test tubes

1478
01:12:09,820 --> 01:12:10,390
and whatnot.

1479
01:12:10,390 --> 01:12:13,810
But rather, an exhibition where we
book some really big space on campus,

1480
01:12:13,810 --> 01:12:17,170
get a couple hundred tables, a
couple hundred power cords, maybe

1481
01:12:17,170 --> 01:12:18,280
a few dozen pizzas.

1482
01:12:18,280 --> 01:12:21,650
Maybe invite our friends at Amazon,
Google, Microsoft, Facebook,

1483
01:12:21,650 --> 01:12:24,670
and the like to maybe bring some
t-shirts, maybe some job opportunities,

1484
01:12:24,670 --> 01:12:26,620
maybe those little squishy balls.

1485
01:12:26,620 --> 01:12:34,300
And we will invite everyone on campus
to see this semester's final project

1486
01:12:34,300 --> 01:12:34,820
submission.

1487
01:12:34,820 --> 01:12:36,910
So it's your opportunity
to not only show off

1488
01:12:36,910 --> 01:12:41,140
your work to your fellow classmates,
but also to others on campus as well.

1489
01:12:41,140 --> 01:12:44,710
Not quite sure what will happen with
the final project in semester's future,

1490
01:12:44,710 --> 01:12:49,640
but we will certainly, I think,
this semester go out with a bang.

1491
01:12:49,640 --> 01:12:52,780
So welcome to CS50.

1492
01:12:52,780 --> 01:12:53,950
We'll see you Wednesday.

1493
01:12:53,950 --> 01:12:55,822
[APPLAUSE]

1494
01:12:55,822 --> 01:12:58,170
[MUSIC - KANYE WEST, "STRONGER"]

1495
01:12:58,170 --> 01:12:59,760
(SINGING) Faster, stronger.

1496
01:12:59,760 --> 01:13:04,480
Now, now that that don't kill
me, can only make me stronger.

1497
01:13:04,480 --> 01:13:09,490
I need you to hurry up now,
because I can't wait much longer.

1498
01:13:09,490 --> 01:13:15,200