This is a quite famous quote:

640k ought to be enough for anybody.

Did Bill Gates say this?

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    Note that proving somebody said something is potentially easy, given a record, while proving somebody never said something is more difficult. – David Thornley May 5 '11 at 12:27
  • @David: Right, but there should be a bit of proof around that at least didn't mention it in something public, like an ad, press release, etc. – PearsonArtPhoto May 5 '11 at 13:37
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    @Pearsonartphoto: There may well be an absence of evidence, and that may be adequate proof that he didn't say it in a large public venue. Am I being too nitpicky? – David Thornley May 5 '11 at 14:05
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    What Bill Gates did say (repeatedly!) is about speech recognition. – ShreevatsaR Oct 26 '11 at 13:25
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    @ShreevatsaR I don't know, when he says "in 5 years the PC will be flat and speech-driven" he is basically talking about the iPhone and he was off by... 5, 7 years? Perhaps a bit too much optimistic, but it's not as if he predicted flying skateboards; those things did come true by 2010. – Tobia Tesan Dec 11 '15 at 11:32
up vote 82 down vote accepted

Bill Gates himself addressed this in 1996 in a column he wrote:

I've said some stupid things and some wrong things, but not that. No one involved in computers would ever say that a certain amount of memory is enough for all time … I keep bumping into that silly quotation attributed to me that says 640K of memory is enough. There's never a citation; the quotation just floats like a rumor, repeated again and again.

Excerpt from: CAREER OPPORTUNITIES IN COMPUTING -- AND MORE, New York Times Syndicate, 1996

He actually addressed it again in 2001:

Do you realize the pain the industry went through while the IBM PC was limited to 640K? The machine was going to be 512K at one point, and we kept pushing it up. I never said that statement — I said the opposite of that.

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    Accepted this as it is more complete . – Lincity May 6 '11 at 5:14
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    I'd hardly call that conclusive. Guy who really should have known better says something embarrassingly wrong and later says "no, of course I didn't say that; I obviously knew better!" (Not saying that's what actually happened, but it's certainly a plausible scenario that happens all the time with other people.) – Mason Wheeler Dec 10 '15 at 14:40
  • Upvoted: The limit came from Intel as, in the 8088 processor used by IBM, the physical addresses were held in 64k blocks. Blocks with addresses between 640k and 1024k were reserved for communication with display and other hardware devices. Since the limit was hardware borne, attributing the limit to Gates would incorrectly argue that the limit was in some way software derived. – James Snell Dec 11 '15 at 12:32
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    @Mason By that argument I can attribute absolutely everything to any person without giving a source and then when they deny it, it's just them trying to save face (actually not that uncommon, Glenn Beck likes to do that regularly). Sure he might have said it, but without any proof that's a weak argument. – Voo Dec 11 '15 at 20:58
  • @JamesSnell: The 8088 was limited to 1,048,576 bytes of directly-addressable storage and 65536 direct I/O addresses. Many prior machines with a limit of 65,536 bytes of directly-addressable storage used a variety of techniques, which would also have been workable on the 8088, to extend storage essentially arbitrarily beyond such limits. It would have been perfectly easy for the PC to have accommodated 786,432 bytes of directly-accessible RAM or even more than that, but there's really not that much difference between 786,432 and the 655,360 that PC-DOS supports. – supercat Dec 11 '15 at 21:32

According to Quote Investigator, the evidence is inconclusive.

In 1985 InfoWorld quoted him as saying

When we set the upper limit of PC-DOS at 640K, we thought nobody would ever need that much memory. (The quote was not sourced)

The way I would interpret this is that he thought PCs and PC-DOS would be dead before the memory limit would be a problem. This was the norm at the time, new computer architectures arrived all the time and backwards compability was a much smaller issue than just a few years later.

In 1989 Gates said, and this is recorded,

I have to say that in 1981, making those decisions, I felt like I was providing enough freedom for 10 years. That is, a move from 64k to 640k felt like something that would last a great deal of time. Well, it didn’t – it took about only 6 years before people started to see that as a real problem.

More details available in the above link.

No, at least not according to Wired:

Check out this feature on the Huntsville Times (Tennessee) Web site, where you can read Bill Gates' impassioned denial that he ever said anything as potentially unprofitable as the quote attributed to him, and where you can also see just how safe our bet really is.

On the site, Gates takes questions from kids.

QUESTION: "I read in a newspaper that in l981 you said '640K of memory should be enough for anybody.' What did you mean when you said this?"

ANSWER: "I've said some stupid things and some wrong things, but not that. No one involved in computers would ever say that a certain amount of memory is enough for all time."

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