> No, all Pentium 3s as well as the Pentium M. Pentium 4 notably didn't suffer from it, but it of course had many, many, MANY other performance issues.

I had to google a bit to confirm this, and seems like I'm not the only one that understood it the way I did:

https://www.vogons.org/viewtopic.php?p=1360606#p1360606

https://www.vogons.org/viewtopic.php?p=1360620#p1360620

Basically, the info I knew was that Katmai had 128 Bits SSE registers but processed it as 2x64 Bits. That info is well reference pretty much everywhere. What is NOT explicitly mentioned is whenever Coppermine/Tualatin maintained that arrangement or had 128 Bits compute units for SSE, so the wording always made Katmai to look like an exception, as if everything else was 128 Bits.

I believe that only the first Pentium 3 core, Katmai, did this.

> This caused some confusion with the 64-bit version of Windows since Microsoft tried to say that x87/MMX shouldn't be used in long mode, but after queries from video processing companies had to document that the x87/MMX registers were enabled and context switched for user mode code.

I have some faint memories of hearing somewhere that Long Mode didn't support x87. I wonder if it is related to this early info you mention and it being Microsoft specific.

Comments URL: https://news.ycombinator.com/item?id=49127026

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