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Comment by kzrdude | Hacker News Reader

Intel keeps making up new names for their x86-64 architecture. Now 'x64' did they use that one before? Is IA-32e or EMT64 not better? Also if you want to find out quickly what they mean by 'x64', why is the article tagged with 'ia64' (which means Itanium).

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- AMD64 -> Original x86 64bit extension from AMD.

- EM64T (EMT64 is a common typo) -> Intel's implementation of AMD64, intel traded SSE3 to AMD for AMD64.

- IA-32e -> Same as EM64T, Intel used this name for a bit, mostly during development.

- INTEL64 -> Intel renamed EM64T to be more in line with AMD64's naming.

- x86-64 -> Overarching instruction set, AMD64 and INTEL64 are implementations.

- x64 -> Shorthand for x86-64.

x86-64 / x86_64 / x64 are just names for the overarching ISA; AMD64 / INTEL64 are implementations.

The AMD64 and INTEL64 implementations aren't actually identical, there are a few differences between them which compilers generally deal with by producing binaries that can handle either implementation.

The x86-64 / x86_64 / x64 thing isn't Intel or AMD's fault, it came about because OS vendors used different terms for the arch. Linux for example added support when AMD64 was the only thing around and it wasn't clear what Intel was going to do, they were still pushing Itanium. So the linux kernel used AMD64 as the arch name. Later when Intel licensed AMD64 linux wasn't about to completely rename the arch (and thousands of packages as a result) so now in linux the AMD64 arch strangely supports both AMD64 and INTEL64 targets. On the other hand Apple used x86-64 and x86_64 in the OSX kernel and Sun / Oracle decided to use x64. Really the OS vendors created this mess in combination with awkward timing of support between AMD and Intel.

From memory, I seem to remember that the x64 name originally came from Microsoft. They certainly make good use of it, at least, so Sun/Oracle isn't alone :)

Just to fill in a (the?) missing piece in an otherwise well assembled puzzle ;)

I can vouch for the fact, though, that internally the Windows team refers to it as "amd64".

Related is the term x32, which is an architecture (from the point of view of the Linux kernel) for x86-64 code designed to run in 0x86-64 32-bit mode.

Why would you do this? Given that you never use 4 GB of memory, you can save a few bytes of memory (32-bit pointers instead of 64-bit) while still getting the extra registers and operations of x86-64 code.

Well, I suppose it wouldn't be expedient for Intel to call it amd64, but of all the nicknames for that arch, I do hate x64 the most. Do people think x86 was a line of 86-bit processors that got slimmed down to make the x64 line?

First generations of consumer x64 processors were named Athlon 64, so you can read x64 as Athlon 64 compatible if you really want uniformity.

x86 also started as unofficial shorthand.

x64 has actually been used for quite a while both inside and outside Intel. It's simply a shorter version of x86-64, with all the other alternatives (IA-whatever and EMT<whatever>) never really catching outside Intel.

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