[Gllug] IA32? IA64? x86...

[Rich Walker]

Andrew Halliwell <ah at gnd.com> writes:

> 
> IA32=386/486/pentium/pentiumII/pentiumIII/pentiumIV
> IA64=Itanium. (Incompatible with IA32)

Actually, ISTR the IA-64 spec includes an IA-32 emulator at the
front, giving it performance roughly equivalent to a 300MHz Pentium Pro,
with power dissipation roughly equivalent to 4 of them... 

If you ever want to roll on the floor laughing at the full nightmares
inherent in IA-64, Paul DeMone's articles in www.realworldtech.com are
worth a look. Apparently the IA-64 Linux Kernel book is also pretty horrifying.


> Another one out soonish though will be x86-64 (Hammer from AMD) which WILL
> have backward compatibility with IA32, but will lose some or all of its
> 64bitness while being compatible...

x86-64 uses "REX prefix" bytes to indicate that the instruction is a
64-bit one, when in 64-bit mode. These prefixes are bytes in the range
0x40-0x4f. So you have to recompile to get full 64-bit mode, because the
ISA has changed slightly.

However, when in compatibility mode, old IA-32 code will run in a 32-bit model as
before, but under a 64-bit OS. Sounds like a pretty neat compromise,
like the old "better Socket 7 CPU" model...

cheers, Rich.



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