Or Intel would have been cut out if they didn't put forth an offering that was less expensive and more performant? When NT4 came out, it ran on Alpha, MIPS, and PowerPC. You could even run (...at about half speed) x86 binaries on the Alpha port with FX!32. Apple has swung a transition like that twice, all the old Workstation vendors went from 68k to their bespoke RISCs, Microsoft could have just slowly transitioned out of Intel parts with no more difficulty than transitioning to IA64. Windows' PE format still doesn't have an elegant Fat binary setup (they have that Fatpack hack in windows-on-ARM, but it's worse than the 90s implementations), but that doesn't mean they couldn't have added one if compelled because the winning x86 successor(s) didn't end up being backward compatible.

The biggest squeeze on 32 bit architectures is the memory ceiling, and Intel was doing PAE to get 36 bit addressing on the Pentium Pro in '95 and kept squeaking by with PAE well into the mid-2000s before most consumers cared. You only got 4GB per-process, and it took a couple years for chipset support to happen. The chipset issue is itself an interesting historical rabbit-hole, only one of the first-party chipsets for the Pentium Pro - the 450GX - which was a many-chip monstrosity, even _claimed_ to support more than 4GB of RAM. I've never found an example of a 450GX configuration with more than one 82453GX DRAM controller as indicated by the documentation to handle multiple 4GB banks to the extent that I suspect it may not have actually worked. By 96/97 there were 3rd party chipsets that could do >4 processors and >4GB, most prominently the Axil NX801 ( https://www.eetimes.com/axil-computer-to-incorporate-pentium... ) sold by DataGeneral as the AV8600 and HP as the HP NetServer LXr Pro8.

Windows NT was dead in all of them by the time IA64 came out.

The point is that NT is portable, and once Merced hit the market in 2001 5+ years overdue and not delivering on any of its performance promises, the only question was "What architecture will succeed x86, because we can cross IA64 off the list." In the same way that when the 432 showed up years late and 5-10x slower than a contemporary Motorola 68000 or 286, the 432 was dead in the water and all the early 80s workstations were built with 68ks and the PC market went with 286s.

I don't know if the absence of AMD64 in 2003 would have made an opening for SPARC or PowerPC or ARM or something else entirely, or maybe the "Let's slap an expansion on the 8080 again, just like the 386 bailed use out after the 432 debacle" scenario was inevitable, but NONE of the compiler-scheduled-parallel architectures panned out in the market, so someone else was going to win.

WinIntel was already into IA64 boat, when AMD64 came to be.

Without AMD64, their partnership would carry on anyway.

I have read one insider account that Intel had its own, different x86-64 instruction set, designed in response to AMD's. It approached Microsoft and asked it to port Windows to it.

Microsoft refused, saying "we already support one failing 64-bit architecture of yours, at great expense and no profit. We're not doing two just for you. There now is a standard x86-64 ISA and it's AMD64, so suck it up and adopt the AMD ISA -- it's good and we already have it working."

Or words to that effect. :-)

I've not been able to find the link again since, but allegedly, yes, the success of AMD's x86-64 has been due to Microsoft backing it. It sounds plausible to me.

I disagree for a number of reasons:

The slow performance would eventually have lead to Intel realizing its bad idea. They would use market share to competitors on different ISA.

Windows at some point would want to be on faster processors and would again run on some of the others. Windows doesn't have undying loyalty to Intel.

Other people then AMD could do a x86 implementation with some 64 bit overlay as well. Transmeta style. That kind of system would beat Itanium as well if it was put on top of a fast RISC processor.

And at some point AMD even on 32bit would massively gain market share as they invested more in faster RISC style processors. So Intel would have massive pressure from the bottom end and the top end. And in any possible future AMD at some point it gone do something with 64 bit.

The idea that the whole industry goes massively backwards and stagnates for years because Intel monopoly doesn't really work in practice.