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Date: Wed, 9 Jul 2003 08:40:59 -0700 (PDT)
From: Tom Samplonius <tom@sdf.com>
To: Brooks Davis <brooks@one-eyed-alien.net>
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cc: Lukas Ertl <l.ertl@univie.ac.at>
cc: Andrey Chernov <ache@nagual.pp.ru>
Subject: Re: HTT on single CPU?
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On Wed, 9 Jul 2003, Brooks Davis wrote:

...
> P4's below ~3.1GHz do not actually provide logical CPU support.

  All the 800Mhz FSB P4s have HyperThreading, regardless of the
clockspeed.  And so do some P4 533MHz FSB chips.  The CPU feature flags
that FreeBSD displays does tell whether your chip supports HyperThreading
or not.  But, as it has already been mentioned, the motherboard and BIOS
need to provide a MP table.  At some later point, HyperThreading will also
be able to be enabled by ACPI.  Either way, if your BIOS and motherboard
pre-date HyperThreading, it just isn't going to work.  Some diligent
motherboard makers may release a BIOS update to allow their older boards
to use HyperThreading, but many would prefer that you buy a new
motherboard!

  Also, Xeons seem to all have HyperThreading now too.  I have a dual P4
Xeon 2.4 that supports HyperThreading just fine.  

> -- Brooks


Tom