Name: 馮-諾依曼架構 - Computerphile (Von Neumann Architecture - Computerphile)
Uploaded: 2021-01-14T10:13:23.000Z
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>> Sean: Professor Brailsford - a lot of people talk about von Neumann architecture and

we've talked about Babbage; we've talked about Turing. Who was von Neumann ?!

>> DFB: We've done a lot about Turing; we've done a fair bit about Babbage, in the

generation earlier. In fact a lot of people, I guess, in the English-speaking

world would regard Turing, in some way, as being the Father of Computing. He came up

with this very important result, in the mid-thirties, about what was computable,

and as we now know. to his credit. he wasn't at all afraid to burn himself with a

soldering iron and try to create hardware. Which he did at Bletchley Park

during the war. So, yes, if he's the Father, if Babbage was the Grandfather and if Ada,

Countess of Lovelace, was the Great-Aunt,

then who on earth was John von Neumann? And why is he mentioned alongside Turing?

Well right at the outset let's say John von Neumann was the impossibly talented,

impossibly charismatic, very wealthy, Uncle to computing. It was he that, in the

mid-1940s, in a way, made it all happen by the force of his own personality. And

kept it, not just in an enclosed community, but encouraged all those who

wanted to build general-purpose computers to come along to this Summer

School and do it.  But that really, I guess, is in the future. It's where we've got to

get to in the von Neumann story. But, yes, you're quite right Sean, to say that one

of the first phrases that almost any computer scientist hears about is The

von Neumann Architecture for computers, which to a large extent we still follow

even now - all of, what 60-70 years later.  So, we've mentioned EDSAC before, we'll

be coming back to mention this very important early computer again. But it is

a von Neumann machine and all it's saying is [that] it's very simple to build a

computer. You need a Store, or Memory as it's more commonly called nowadays, to

hold your instructions and your data. You need a

control unit, often called a CPU now. And you need an arithmetic capability - the

ALU, the arithmetic and logic unit. Again many of you will know in modern chips

those two are often combined into what we just call "the CPU chip" nowadays.

And you need input devices of various sorts leading back to people's Teletypes [with]

input/output devices for backup storage, disk and so on. You need to be able to do

input and output. So there it is. It's just one, two, three, four, five boxes - that

is the von Neumann architecture. And it's very, very similar today. There was a big

debate at the time about that Store that Memory. Shouldn't you, for safety's sake,

put the instructions of your program in a different sort of memory to your data?

Wouldn't it be safer to do that and better in some ways? On the other hand,

clearly, if you've got a good memory technology, that works, the temptation

might be just to put them [instructions and data]  in separate areas of that same technology and try

and take some sort of precaution about them not interfering with each other. In

EDSAC the only way to get into a subroutine and get back out of it again

was to over-write part of your program instructions! Let's just return back to

this incredible character John von Neumann. How does he fit in alongside

Alan Turing? Well, like I said, he's the older, impossibly talented, Uncle. Did

Turing and von Neumann know each other? Oh yes they did! They were both, basically,

trained as mathematicians. Von Neumann -  it's hard to know where to begin and

where to end. You can't exaggerate enough  about how

good he was. He was Hungarian and his Hungarian name - where they give surnames

first - was, I think, Neumann Janos. His father was very, very wealthy and

when one was quite young the family became ennobled in Hungary. [They] became

basically at the level of Baron -  hereditary Baron I think

over here. Janos was very talented; he was a childhood prodigy. He could divide one

eight-digit number by another eight digit-number in a fraction of a second

when he was aged about 6. He loved history; he was a multi-talented polymath

he easily came top of the class he effortlessly took in detail. And that's

the first thing that all of his mathematics contemporaries said about

him was his sheer speed of picking up new ideas and seeing the ramifications

of them. So he was notorious even as a teenager, and as a maths undergrad. He did

his early education I think up to PhD level in Budapest. He almost naturally

ended up at a place we mentioned before in connection with Godel and Hilbert.

I'm talking, of course, about Gottingen University in Germany. So Neumann Janos

makes the journey, via a PhD, to becoming effectively the research assistant

to the superstar David Hilbert at Gottingen. But because his family

had been ennobled he's not Janos Neumann  any more - Neumann

Janos sorry  - he's Johann von Neumann - impossibly talented. Hilbert his

supervisor, at a seminar given by Johnny,

John,  Johann (!)  asked who his tailor was. Because his impossibly smart

pinstripe suit was just a complete knockout. So he was a legend almost the

moment he got there and did some fabulously important work there. It was

obvious that for somebody of his talents he was going to get a full Professorship

very quickly indeed. I think he became impatient, waiting for it to happen at

any German university. So, in the late thirties  - '37-'38?  Somewhere around there anyway -

Anyway he got an offer from Princeton, in New Jersey. And that was, I don't know,

very timely. It all fitted in together very well. As part of his tours of Europe,

giving seminars, and on his way to Princeton, I think he met Turing in the

mid-thirties in Cambridge. Because he gave seminars there

and I think a lot of mutual respect grew up. I mean, obviously, Turing being in awe of

von Neumann wouldn't be so exceptional. But after that 1936 paper of Turing's,

about decidability, following on from Godel and all that, von Neumann rated

Turing - there was no question about that. This was evidenced by the fact, you will

recall - those of you who have seen my previous videos - that Turing also took a

sabbatical and worked with Alonzo Church at Princeton.

Well, von Neumann was there by that time. Von Neumann was such a superstar, they not only

made him [full] Professor of Mathematics at Princeton, at an absurdly early age -

probably about 30, something like that. But some of you will recall, right next

door to Princeton - about a mile and a half across the meadows - is the Institute

for Advanced Study which had been endowed in the early 1930s by a

multi-millionaire. And this really was the ultimate Club to be invited to join.

You've got to be of the quality of Einstein, who accepted the invitation.

Hermann Weyl one of the founders of quantum mechanics; Godel - we know about

Godel. Godel was invited to just come to IAS - Institute for Advanced Study at

Princeton - stay as long as you like. Yes, you're a Professor; everything found: food

accommodation; the lot. All we want is to have the greatest minds here. Von Neumann

was offered a professorship in that community, I think at age 35 - maybe

slightly younger. Unbelievably young. He'd hardly been at Princeton a year or two, as

an ordinary mathematics professor. Everybody thought "This is a truly

phenomenal person". He reminded many people of absolute superstars like

Newton, Gauss, Euler, Einstein, Hilbert himself. Even at early to mid-

thirties they could see that potential in him, there. So, yes, Turing visits

Princeton in 1938 - worked with Alonzo Church - but also of course had frequent

interactions at seminars with von Neumann And then came the big question,

if you recall, for Alan Turing: "Should I return to England and do my patriotic