P4 and Hyperthreading

Steve_L_Smith at Dell.com Steve_L_Smith at Dell.com
Sat Jan 11 15:06:47 PST 2003

Just to clarify:
Hyperthreading was introduced in the Prestonia version of the  Xeon
processor, January 2002 I believe. This is the 13micron device rather than
the previous Foster 18micron device. Speeds overlapped at launch, Xeon
Prestonia was launched at I think 1.8, 2 and 2.2GHz, and Foster processors
co-existed for a while. At this time the only products shipping with Xeons
were workstation class products using the Intel 860 chipset - all server
class products (e.g. those based on Intel 7500 and Serverworks GC class
chipsets) came later and use Prestonia Xeons.

Recently Intel have also incorporated Hyperthreading on Pentium 4. The
confusion arises partly because of Intel's Pentium 4 and Xeon nomenclature.
To be incredibly pedantic (sorry:-) the Pentium 4 is a single processor
device, it has no ability to work in an SMP machine. The Xeon (note it is
Xeon, not Pentium 4 Xeon) is the multi-processor variant of the Pentium 4,
that is, it contains additional on-chip logic to allow it to work in an SMP
machine (subject to an appropriate chipset). Note that there is no such
thing as a Pentium 4 Xeon, unlike the Pentium III Xeon (also note the change
from Roman to Arabic numerals).

So - you can have a single processor system based on Pentium 4, you can have
a single processor system based on Xeon (i.e. a system with only one Xeon
processor in it (although there is not a lot of point)), and a
multi-processor system of Xeons. Just to complete (and confuse further) the
picture, there is also a device called the Xeon MP. This is a Xeon processor
designed for 4-way and up SMP systems, containing larger caches but slower
clock speeds. This device is still (at least I believe so) based on Foster
(18 micron) technology but does include Hyperthreading.

If anyone out there from Intel could confirm or add to this I'm sure we'd
all appreciate it.

So there you have it!

Steve Smith
HPC Business Manager
Dell Campus, Cain Road, Bracknell, RG12 1FA, UK
Direct: +44 1344 372037
Switchboard: +44 1344 812000
Fax: +44 1344 372359
Mobile: +44 7802 594874
email: steve_l_smith at dell.com

-----Original Message-----
From: Henderson, TL Todd [mailto:Todd_Henderson at isl-3com.com]
Sent: 08 January 2003 19:49
To: 'Patrick Geoffray'
Cc: 'beowulf at beowulf.org'
Subject: RE: question about Intel P4 versus Alpha's

These are P4 2.4 ghz and I didn't find anything in the bios about it.  I
thought I had read on Intel's website that hyperthreading was only in the
3.xx ghz P4's?


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