My impression is that the 640KB quote started as a huge simplification of the arguments Bill Gates made in an article in an early PC Magazine (might have been a

My impression is that the 640KB quote started as a huge simplification of the arguments Bill Gates made in an article in an early PC Magazine (might have been a rival magazine instead - it has been 35 years since I read it) defending IBM's decision to "waste" so much of the precious 1MB address space on I/O. And he was right: without this networking and betters graphics would have been much harder to do later on.