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I was reading a book which describes a historical perspective:

Pentium 4E (2004, 125 M transistors). Added hyperthreading, a method to run two programs simultaneously on a single processor, as well as EM64T, Intel’s implementation of a 64-bit extension to IA32 developed by Advanced Micro Devices (AMD), which we refer to as x86-64

I'm a little bit confused here, here are my two questions:

  1. Does it mean that 'x86-64' is just an alias of 'EM64T'?

  2. Is IA32 developed by AMD? Isn't IA32 designed by Intel and first implemented in the 80386 microprocessor in 1985? See Wikipedia.

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    $\begingroup$ Short answer: AMD came out with the first mainstream 64-bit processor and instruction set architecture that was backwards compatible with 32-bit Intel processors while Intel was dinking around with Itanium. IIRC, Intel would later just license amd64 back and add their own extensions. en.wikipedia.org/wiki/X86-64#History_2 $\endgroup$
    – selbie
    Jul 5, 2020 at 8:29
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    $\begingroup$ Q2 looks like it is a question about understanding an English sentence and thus off-topic here. It might be on-topic on English Language & Usage, but as always, make sure to take the tour, read the help center, especially the on-topic, off-topic, and How To Ask pages, read the meta site, browse the questions on the main site to get a feel for what is and isn't considered a good question, and search for duplicates before asking. $\endgroup$
    – Jörg W Mittag
    Jul 5, 2020 at 9:21

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Q1-does it mean that x86-64 is just an alias name of EM64T?

The original name for the architecture is AMD64.

That is also the marketing name that AMD uses for that architecture.

When Intel licensed it from AMD, they first called the feature CT, then IA-32e, then EM64T, and most recently Intel 64. Those are Intel's marketing names. Note that Intel 64 contains extensions on top of AMD64 as well.

x64 is not an official name. It is a marketing name created by Microsoft in order to refer to both Intel's and AMD's (as well as other vendors') implementations without using the name of one of the two main competitors.

x86-64 is not an official name. It is a marketing name used by many vendors in order to refer to both Intel's and AMD's (as well as other vendors') implementations without using the name of one of the two main competitors.

x86_64 is the GNU Autotools architecture designation used in tools such as Autoconf, Automake, and GCC.

IA-32 is, I believe, a term that Intel only introduced after they started working on IA-64. Until then, the architecture was colloquially known as x86, but did not actually have a name.

The bottom line is that you can mostly use the terms AMD64, IA-32e, x86-64, and x64 interchangeably, and people will probably understand what you are talking about. But, the official name for the architecture is AMD64, but that can also refer to AMD's specific implementation of that architecture (which may have AMD-specific extensions). Whereas IA-32e is Intel's specific implementation of the AMD64 architecture, which may have Intel-specific extensions.

Q2- And is IA32 developed by AMD?

No, it isn't.

isn't IA32 designed by Intel and first implemented in the 80386 microprocessor in 1985?

Yes, it is, although the name IA-32 came later.

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