Athlon 64: How AMD turned the tables on Intel

Fun fact: Bob Colwell (chief architect of the Pentium Pro through Pentium 4) recently revealed that the Pentium 4 had its own 64-bit extension to x86 that would have beaten AMD64 to market by several years, but management forced him to disable it because they were worried that it would cannibalize IA64 sales.

> Intel’s Pentium 4 had our own internal version of x86–64. But you could not use it: we were forced to “fuse it off”, meaning that even though the functionality was in there, it could not be exercised by a user. This was a marketing decision by Intel — they believed, probably rightly, that bringing out a new 64-bit feature in the x86 would be perceived as betting against their own native-64-bit Itanium, and might well severely damage Itanium’s chances. I was told, not once, but twice, that if I “didn’t stop yammering about the need to go 64-bits in x86 I’d be fired on the spot” and was directly ordered to take out that 64-bit stuff.

https://www.quora.com/How-was-AMD-able-to-beat-Intel-in-deli...

The story I heard (which I can't corroborate) was that it was Microsoft that nixed Intel's alternative 64-bit x86 ISA, instead telling it to implement AMD's version instead.

Microsoft did port some versions of Windows to Itanium, so they did not reject it at first.

With poor market demand and AMD's success with amd64, Microsoft did not support itanium in vista and later desktop versions which signaled the end of Intel's Itanium.

Microsoft supported IA-64 (Itanium) and AMD64 but they refused to also support Yamhill. They didn't want to support three different ISAs.