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For example, IA64 and AMD64 is 64-bit architecture for computing. But why it is different? Is there no industry-standard for 64-bit architecture (for desktop computer)? And what make those architecture different?

user50334
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  • This question appears to be off-topic because it is about – Scott Pack Jun 29 '13 at 02:16
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    This question appears to be off-topic because it is entirely theoretical. Furthermore, it appears to be a very poorly worded homework question. – Skyhawk Jun 29 '13 at 02:20
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    Indeed, if I were to give this question as a homework assignment, I would have worded it more clearly. Students have a hard enough time as it is. – tylerl Jun 29 '13 at 02:22
  • I am sorry for my bad English. I just wanted to know why there is more than 1 standard for 64 bit desktop computer (But only x86 32-bit standard for desktop computer). I was watching [Mac Megahertz Myth](http://www.youtube.com/watch?v=PKF9GOE2q38) , and wanted to know more about computer arch. – user50334 Jun 29 '13 at 05:06

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IA64 = Intel Architecture 64-bit. Commonly known as Itanium or Itanic (a reference to the Titanic, and how it the unsinkable sank essentially immediately). The architecture has been an abject failure. It used a completely different architecture from existing x86 processors, territory the software industry was completely unfamiliar with, and fora variety of reasons shunned.

AMD64 = AMD knew Intel was working on Itanium, and in a bet against the architecture developed 64-bit extensions to the existing x86 architecture. Because this architecture works as an extended mode of the standard x86 arch, and was full backwards compatible in the same way that the 32-bit 80386 was when 16-bit 80286 processors were popular people embraced the change they were familiar with.

AMD64 is essentially the standard for 64-bit PC computing. IA64 is incredibly rare, most commonly found in HP Clusters built in the early/middle 2000s. There are also SPARC and MIPS 64-bit architectures, though these are extremely uncommon in PCs. Why all the architectures, competition...

Chris S
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Back when 64-bit architectures started becoming available to the x86 space, there was a war over which ISA would win. Both AMD and Intel proposed slightly different standards for that. Both trumpeted their own standard as the One True Standard.

AMD won the most market acceptance, and EM64T (later Intel64), their main line 64-bit architecture slumped off into obscurity. You used to see Linux distros with kernels and packages compiled for both, but that stopped years ago.

As I remember it AMD64 won because it handled 32-bit interoperability slightly better, and that was a critical differentiator during the 32 to 64 bit transition years.

IA64 never achieved any significant acceptance.

sysadmin1138
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    AI64 has no ability to run x86 code natively, even Itanium 2 uses a strange interpreter that runs directly on the CPU to emulate x86 compatibility. Itanium processors were slow out of the gate, and massively slower for existing applications upon release. Intel screwed themselves from the start. – Chris S Jun 29 '13 at 02:05
  • @ChrisS Ah, I'm confusing IA64 with X86-64, which was their true 64-bit competetor. – sysadmin1138 Jun 29 '13 at 02:06
  • To be fair, Intel's was called EM64T and then IA-32e and then Intel64. And it still exists. – Ignacio Vazquez-Abrams Jun 29 '13 at 02:10
  • @IgnacioVazquez-Abrams It does, but they've since extended it to include the ADM64 specific instructions. – sysadmin1138 Jun 29 '13 at 02:14
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Intel and AMD both produced 64-bit standards for their chips. Intel's was more of a redo-from-scratch, while AMD's was a backwards-compatible extension to x86.

AMD's backwards compatibility made it a clear winner as 64-bit capability could be a feature that you could add to your chips, but it wouldn't be mandatory. So a chip that supports AMD 64-bit instructions can be used with 32-bit or 64-bit operating systems, and if used with 64-bit OSes can still run 32-bit code.

Today few devices use IA64 anymore.

tylerl
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