Name: CS50 2018 - Lecture 5 - HTTP, HTML, CSS
Uploaded: 2018-10-28T09:07:48.000Z
Duration: 1 h 46 min 19 s
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And today, we transition from the world of C and, with it, pointers

and some of the struggles that you might have felt over the past few weeks

to a more familiar world, that of web programming.

I'm using web browsers and mobile devices and laptops and desktops

and creating more graphical and more interactive experience

than our traditional command-line terminals have allowed.

And we'll see, though, along the way that a lot of the ideas that we've

been exploring over the past few weeks are still going to remain with us.

And we're going to see them in different ways.

We're going to see them in the form of other languages and other syntax.

But the ideas will remain quite reminiscent of what

So TCP/IP is perhaps the most technical way

and the most low-level way we can quickly make the web uninteresting.

But you've probably, at least, seen this acronym somewhere, maybe

on your Mac, your PC, some setting maybe once upon a time.

And this, actually, just refers to a protocol

or, really, a pair of protocols, languages of sorts

that computers speak in order to transmit information

And this is what makes most of the internet today work.

The fact that you can pull up your laptop and desktop

and talk to any computer on the internet is because of these protocols,

conventions that humans decided shall exist some years ago.

And they just dictate how computers intercommunicate.

In our human world, you've probably, at some point, sent or received a letter.

These days, it's perhaps more electronic.

But, at least, you've gotten one such letter

from probably a human, maybe a grandparent or the liked,

But before you can actually send that message to the recipient

and put it through the US mail or the international mail services,

DAVID J. MALAN: Yeah-- so some kind of address.

DAVID J. MALAN: So where they are might include a street address and a city,

a state, a ZIP code in the US, or a postal code, more generally,

and the country, if you really want to be specific.

And so all of that goes on the front of the envelope,

And then what often goes on the top left-hand corner in most countries?

So the return address-- so that if something goes wrong,

albeit infrequently, that letter can get-- make its way back to you,

and also the recipient knows just immediately who actually sent them

So that is enough information to get a letter from point A

to point B because these addresses, these postal addresses

in our human world, uniquely identify houses or buildings or people,

So right now, we're at 45 Quincy Street, Cambridge, Massachusetts, 02138, USA.

That is probably enough specificity for anyone in the world

to mail us a postcard saying "Hello world" in written form

Meanwhile, if we wanted to send something to the Science Center,

1 Oxford Street, Cambridge, Mass, 02138, USA, that's its unique address.

So it stands to reason that computers, including our own Macs and PCs

and Android phones and iPhones and the like,

all have unique addresses, as well, because, after all, they

And they need to get bits, zeros and ones, from point A to point B.

But they're not quite as verbose as those kinds of addresses.

Computers have what you probably know as IP addresses,

And this just means that humans decided years ago

that every computer in the internet is going

And that number is generally of the form something dot something dot something

And, as it turns out, each of these somethings between the dots

And now, after all these weeks of CS50, your mind

How many bits must each of these numbers be taking up

But yes, this is eight bits, eight bits, eight bits, eight bits,

which means the numbers that we humans use to uniquely identify our computers

Well, there's probably another number that can roughly come to mind.

If you've got 32 bits, how high can you count, roughly speaking, from 0 to--

And we brought that up in week 0 with a four billion-page phone book,

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CS50 2018 - Lecture 5 - HTTP, HTML, CSS

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