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Comment by chrisseaton | Hacker News Reader

> x86_64

I don't know why people still use these crazy names. x86_64, x64, etc. The people who designed it call it AMD64. Let's call it that.

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> The people who designed it call it AMD64. Let's call it that.

They originally called it "x86-64". Recycling a comment of mine from 4 months ago (https://news.ycombinator.com/item?id=22282127):

The "x86-64" name is the original one, and came from AMD themselves: https://web.archive.org/web/20000817071303/http://www.amd.co... (and "x86_64" is obviously an alias for where a hyphen is not an allowed character, like identifiers on many programming languages).

The "x64" name came from Microsoft, probably due to file name length limitations (this was before Windows XP unified the Windows 9x and Windows NT lines).

IIRC, the "AMD64" name came later, probably to distinguish it better from Intel's IA-64 (Itanium).

Windows 9x had long file name support.

If we’re speculating, my guess is that they chose “x64” for symmetry with “x32”. Or woodruffw’s suggestion: https://news.ycombinator.com/item?id=23513591

> my guess is that they chose “x64” for symmetry with “x32”

x32 only came out around 2011. It's younger than x64 which came out around 2003, so that can't possibly be the case.

Makes sense. What do you mean by it “came out”?

Looks like “x32” was used at least as far back as 2009: http://www.utteraccess.com/forum/office-2010-x64-bit-qu-t191... . Not much earlier than 2011, but just FYI.

> What do you mean by it “came out”?

It was announced in August 2011, that's when the code was shown for the first time.

https://lkml.org/lkml/2011/8/26/415

> Looks like “x32” was used at least as far back as 2009: http://www.utteraccess.com/forum/office-2010-x64-bit-qu-t191.... .

This is a great example because that person is confused by these terrible names - they've seen the name x64, and they assume there must be an x32... but there wasn't, back in 2009. They mean 32-bit x86, which is not the same thing as x32.

We’re talking about different things. I’m talking about people using “x32” to refer to x86. Hence my confusion about “x32” “coming out”.

Unfortunately names get baked into things, so it's not as easy to change as just saying "let's change". "x86_64" is what Linux 'uname' and the gcc triplet naming conventions use, so that's what I go with, because it's the closest there is to a "standard" name in the software ecosystem I spend most time in.

AMD64 and EM64T are actually not identical. Though it doesn’t usually matter much in usermode, they are by specification not the same architecture. x86_64 is an umbrella for the various almost identical 64 bit extensions to x86.

I have encountered that unfortunate fact when doing my term homework for a graduate level computer architecture course. Failure to detect or misdetection of on which kind of x86-64 you run will cause type confusion and finally crash your code.

Would you mind sharing what you were doing where the difference mattered?

I did not perform an applied experiment, more a literature and benchmarks review; but Mayhem and Nubok[0] say this:

> Near branches with the 0×66 (operand size) prefix behave differently. One type of CPU clears only the top 32 bits, while the other type clears the top 48 bits.

This is more than enough to send your code into wrong address and possibly cause a crash.

[0]: https://superuser.com/posts/383943/

> The people who designed it call it AMD64

They did not, at the time. I have a set of original manuals for the AMD "x86-64" architecture (with a dash, not an underscore).

Yes and I think it had another code-name before then. But taking x86-64 and making it x86_64 is even more lunacy - why change the punctuation to give us another subtlety different name?

Why does everyone want to invent their own name for this thing?

> why change the punctuation to give us another subtlety different name?

Because one is a legal part of a symbol name in C and the other only works in lisp.

> But taking x86-64 and making it x86_64 is even more lunacy

There are contexts where hyphens are not allowed but underscores are, like identifiers in many programming languages. Replacing the hyphen with an underscore is an obvious workaround.

Author here: I use AMD64 and x86_64 interchangeably (with a slight preference for the latter when publishing something, since it has more Google results than the former). I agree that the proliferation of names is an unfortunate mess.

FWICT, "x64" is mostly limited to Microsoft. I wouldn't mind that one being thrown out.

Internally a lot of Microsoft people still call it amd64.

For example the windows build flavor is called amd64fre or amd64chk. (chk is a debug build, fre is what most humans use)

X64 is quicker to say and seems widely understood.

> FWICT, "x64" is mostly limited to Microsoft. I wouldn't mind that one being thrown out.

Yes, that one particularly, since 86 and 64 don't even have anything to do with each other. One is a product number and the other is a word width - why did they replace one with the other?!

Complete shot in the dark, but I wouldn't be remotely surprised if there's a `TCHAR arch[3]` somewhere deep in MSBuild.

"x86" fits nicely in there and they couldn't refactor it in time, so they just decided to go with "x64".

x86_64 clearly shows it to be an extension of x86. The people designing things are not necessarily the people we should be listening to when consider what to call something, too; sometimes they're kind of bad at naming.

It's only called x86_64 instead of amd64 because Intel was able to lobby the right people to not use AMD's name when implementing the standard AMD designed and published.

Sure, but I don't think the result was necessarily worse ;)

Intel calls it IA-32e which I assume means Intel Architecture 32-bit w/ Extensions for 64-bit, 128-bit, 256-bit, and 512-bit computation. My preferred term for x86_64 is NexGen32e due how AMD bought NexGen which sold so much better than IA-64 that Intel ditched it and licensed the IP.

I think they call it Intel 64. IA-32e is an execution mode, not an ISA.

https://software.intel.com/content/www/us/en/develop/article...

You left the DEC reference out of there.

The K6 was a very competent chip but the you can see in the how the high level architecture starts to look much more like the EV6 with the Athlon series.

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