[Gllug] IA32? IA64? x86...

[Jonathan Harker]

At 22:09 03/10/2002, you wrote:
>Hi guys
>
>I'm getting a bit fuddled here...
>
>Can one of the hardware gurus explain what's what? Which processors are IA32
>(i{3|4|5}86?), which IA64? Where does i686 fit in the scheme? How is the
>Itanium related (if at all?)

Okay here goes...

Intel have 2 main "machine code" (?) languages - IA32, which was introduced 
with the 386 processor waaay back, and IA64, which it introduced with the 
Itanium.

IA32: Introduced with the 386, Intel's first 32 bit PC chip. They then 
renamed it the 386-DX and brought out a crippled 386-SX which had a 16 bit 
bus so you could stick it in older motherboards (32 bit motherboards were 
expensive and fighting between IBM's MCA bus, as used on the PS/2, and the 
EISA bus; PCI hadn't arrived yet). The 486 came out with a faster core, 
redesigned memory management, and a floating point unit on the 486-DX 
(formerly an additional 387 chip was required alongside the 386 for 
efficient FP) The Pentium (they couldn't trademark 586, even with an 'i' in 
front of it, so they started naming them) added a better bus and some extra 
instructions (eg. the infamous FDIV bug). Then Pentium Pro was the 686 
evolution, mainly a die shrink, newer pipeline, faster floating point, but 
they priced it well out of reach for most people. With another die shrink 
(to 0.35 micron IIRC?) Intel added MMX instructions to its Pentium and 
Pentium Pro chips, which then became the Pentium MMX, and Pentium II, 
respectively. The Pentium III was a slight tweak adding SIMD (single 
instruction multiple data), and a die shrink. Pentium 4 is a complete 
redesign, but still fundamentally a 686 IA32 chip.

Confusion of nomenclature is rife since Cyrix and AMD were doing clones of 
Intel chips. AMD K5 was a Pentium clone, K6 (to which they added their own 
version of MMX and SIMD, called 3D Now, and marketed it as a 686 chip) and 
Cyrix 6x86 were competitors to the Pentium II, but fit into the old Socket 
7 (for Pentium chips) rather than the more expensive and proprietary Slot 1 
(Pentium II, III). In late 1999 AMD released the Athlon (K7), and marketed 
it as a 786 generation chip. It has remained superior to or on par with the 
Pentium III and Pentium 4 in performance ever since.

IA64: Used on Itanium, which uses Intel's new EPIC marketecture, which is 
some evolution of RISC (or is it semi-parallel? Someone feel free to 
clarify?). Software requires recompilation to gain any performance benefit 
from Itanium, as IA32 is sort-of emulated on the chip, and runs slower than 
a Pentium III at the same MHz as a result. Which is why it has generally 
bombed.

x86-64 is AMD's take on 64 bit processor architecture, which seems to me 
much more sensible; essentially it is IA32 with additional 64 bit versions 
of the important instructions (much as Intel's 386 was a 32 bit extension 
of the 286). This means IA32 stuff will work fine, with no emulation layer. 
We'll see very soon when they release the Hammer at the end of the year!

CISC - Complex Instruction Set Chip - means that the chip instructions can 
have varying lengths and take varying arguments. All Intel IA32  chips and 
various clones, AMD Athlon.
RISC - Reduced Instruction Set Chip - instructions and data are all the 
same lengths, which makes pipelining and chip design (theoretically) 
faster, simpler, more efficient, etc. PowerPC, Alpha, IBM Power4, MIPS, etc.
EPIC - As far as I can tell, mostly marketing bollocks to hide the fact 
that it's really CISC. Itanium.

(phew)
night night,

Luv Jon.



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