Name: 2019年律師的CS50--編程語言篇 (CS50 for Lawyers 2019 - Programming Languages)
Uploaded: 2021-01-14T10:20:38.000Z
Duration: 1 h 25 min 29 s
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DAVID MALAN: There's any number of languages in which we can communicate,

程度副詞

But computers, of course, only understand binary zeros and ones.

And so somehow we have to communicate our thoughts-- ultimately in binary--

in order to solve some problem with a computer.

But certainly, we don't want to program computers by writing zeros and ones

and memorizing the patterns that they'll understand,

so we do somehow need to adopt a process by which

we can express our thoughts and the solutions to the problems

that we have in mind but in such a way that the computer can understand them.

Now it turns out it's quite meaningful when

you see something like Intel inside or AMD

or any number of other computer manufacturers

that make what are called CPUs, Central Processing Units, which

you can think of as the brains of sorts inside of your computer.

Well, turns out that Intel and AMD and other companies

have decided in advance what patterns of bits--

zeros and ones-- that their CPUs understand.

A certain pattern of zeros and ones might represent addition.

Another pattern of zeros and ones might represent subtraction or multiplication

or division or the act of moving information around in memory

And so those patterns are very much computer or CPU specific.

And frankly, I'd like to be able to write software and write

code that can run on your computer and my computer

and some other manufacturer's computer without really having

So there too it would be nice if there's a process, a workflow, a tool

chain via which we can communicate our thoughts in a fairly accessible way

but have them ultimately translated into those zeros and ones.

So what is it that Intel inside really means?

What is it that a CPU actually understands?

Well, it's what's called machine code, zeros and ones that ultimately dictate

what the computer should do-- add, subtract, multiply, or something else

That machine code literally might look something like this.

In fact, let me give you just a moment and from all of these zeros and ones,

can you glean perhaps what this very program would do if run on a computer?

Well, odds are you couldn't imagine what this would do because even

But if it turns out you fed these very zeros and ones to a computer,

it would print out on the screen quite simply

"hello world," which is sort of the canonical phrase, one

of the first phrases ever printed on a computer screen back in the day

when computer languages were first being invented.

Now you, of course, would never know that, should never know that,

nor should even the most sophisticated of programmers

because this is just too low of a level to communicate one's thoughts in.

Far more compelling would be to operate at a level closer to English

or whatever your spoken language might be.

And so quickly, when humans invented computers decades ago,

did we decide we need something different from machine code.

We need something at a higher level of abstraction,

if you will, something that's more familiar to us

but that's close enough that the computer can somehow figure out

Assembly code is an example more generally

of what's called source code, which is typically

English-like syntax more familiar to us humans that can somehow be translated

And assembly code, which is one of the earliest

incarnations of this general idea, looked a little something like this.

Now it too looks pretty cryptic, though hopefully

not quite as cryptic as just seemingly random patterns of zeros and ones

because there is some organization to this text here.

It's not quite English-like I would say, but there's

some familiar sequences of characters that I can perhaps

I see words that look a little familiar-- push queue or at least push,

Sub-- maybe that means subtract or call, as in to call a function

or a procedure, xor and add and pop and others--

these seem to be reminiscent of English words.

and I would surely need a manual in order to figure out what these mean--

this is a standardization of how you might communicate instructions

Indeed, all of those keywords push queue, move queue, sub queue and so

forth are literally called instructions, and those

are the names given to the instructions, the commands that Intel and AMD have

decided that their brains, their CPUs shall understand.

To the right of these instructions is some cryptic looking syntax now--

dollar signs and percent signs, commas, and others.

Well, those are used to communicate what are called registers.

It turns out that the smallest unit of useful memory

A register might be eight bits back in the day, 32 bits

And that is really the smallest piece of information

that you can do some operation on, the smallest unit of information

that you can add to something else or subtract from something else and so

So when a CPU is doing its arithmetic-- addition, subtraction, multiplication,

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2019年律師的CS50--編程語言篇 (CS50 for Lawyers 2019 - Programming Languages)

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