Replies to post #26617 on Advanced Micro Devices Inc (AMD)

[fastpathguru]

Ahhh, so a mere microcode edit used to bring a processor from x86 to x86-64 only requires an aborted incompatible 64-bit implementation to already exist on-die?

I wouldn't call that exactly supportive of your "IA32E is an instruction extension - a microcode edit." claim... From the context of the thread, it was not reasonable to assume your "microcode edit" depended upon already existing 64-bit infrastructure in Prescott.

Here's an earlier quote in the thread from you:

"I don't see IA32E as anything more than new instructions, like SSE-x."

Well duh, of course it's "just" new instructions. But do you think "SSE-x" could also be implemented with mere microcode changes?

fpg

[HailMary]

If you have a 64-bit ALU, you can change the microcode to make the instruction format whatever you want.

There is a lot more to a CPU than a simple ALU. There are lots of special registers, tables, control lines, etc. that need to be changed to support a 64-bit architecture, and especially a hybrid that can support many modes. Now there are some things you can do in microcode to make your processor look more like another architecture, but performance is going to be terrible if you don't have some optimized hardware to back it up. Addressing and mode changes are not isolated to just microcode changes.