Originally posted by: Nothinman
The OP mentioned making Vista 64-bit only. The only 64-bit technology that would be possible with is x86-64 because as you said, the alternative 64-bit architectures aren't viable. So it isn't really about the width of the registers... it's about "x86-32" or x86-64 because those are the only two options on the market.
And my reply about PAE wasn't directed at the OP but at mechBgon, I even quoted his post in mine as usual so that it's difficult to confuse who and what the comment is about.
And width of registers has nothing to do with 32-bit vs 64-bit or x86 vs AMD64 either, SSE registers have been something like 96-bit or 128-bit for quite some time so if you really needed them you could use them without producing a 64-bit binary.
Yep, 128I'm pretty sure, although I haven't kept up with the latest Core 2 architecture, maybe Intel added more. There's also a lot more SSE registers than there are GPR's. But again, you're speaking in general terms. x86 CPU's are what we're talking about here, and there's only two types worth talking about. The 32-bit ISA and the 64-bit ISA. AMD chose to develop a 64-bit processor rather than extend the 32-bit ISA with PAE and adding more GPR's. Unless we're in the Highly Technical forum discussing all those other architectures, I think it's safe to assume that anyone who's talking 32-bit vs. 64-bit is talking about the specific x86-64 ISA... not a 64-bit processor in the most general terms possible.
So when someone asks, "why 64-bit?" They're asking, "Why an AMD64 or EMT64 processor with a 64-bit version of Windows rather than a 32-bit version of Windows?"
If the increased physical address space was the ONLY reason "64-bit" mattered, sure, PAE would be reasonable solution. But it's not the only reason. The fact that the A64 and Core 2's are 64-bit processors means little compared to the other features those processors that happen to be 64-bit have. I don't know for sure, but I suspect AMD figured if they're going to modify the ISA, why not lay the foundation for the future. Maybe some day we will be working with applications that benefit from the enormous dynamic range of a 64-bit processor. It'll suck not to have that when you need it, but what harm does it do to have it and not need it?
So that's my point... it's not a processor's "64-bitness" that matters, it's the features of the x86-64 ISA that matter, and if developers would start taking advantage of them there would be a reason to move to 64-bit. But they're not... so here we are, not much worse of running a 32-bit version of Windows than we are running a 64-bit version, and sometimes better.