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Subject: If you own a P4 or P4 Xeon "Get Ready for Intel's Hyper-Threading Tech"

Author: Nolan Denson

Date: 15:32:17 01/15/02


Currently the way most CPU manufacturers improve performance within a CPU family
is by increasing clock speed and cache sizes. In the case of our hypothetical
CPU, doing either or both of those things would improve performance but we're
still not using the CPU's full potential. If there was a way for us to execute
multiple threads at once we could make more efficient use of the CPU's
resources; this is exactly what Intel's Hyper-Threading technology does.

Hyper-Threading is the marketing name applied to a technology that has been
around outside of the x86 realm for a little while now - Simultaneous
Multi-Threading (SMT). The idea behind SMT is simple; the single physical CPU
appears to the OS as two logical processors but the OS does not see any
difference between one SMT CPU and two regular CPUs. In both cases the OS
dispatches two threads to the "two" CPUs and the hardware takes it from there.

Hyper-Threading was officially announced at the Intel Developer Forum last fall
and it was demonstrated running on a Xeon processor performing a Maya rendering
task. In that test the single Xeon with Hyper-Threading enabled was 30% faster
than a regular Xeon CPU. The performance benefits were definitely impressive and
even more exciting was the unspoken fact that Hyper-Threading is actually
present on all Pentium 4 and Xeon cores; it is simply disabled.

The technology has not officially been debuted on a CPU yet however those that
have purchased the new 0.13-micron Xeon processors and used them on boards with
updated BIOSes may have been surprised with an interesting option - to
enable/disable Hyper-Threading.

For now, Intel will be leaving Hyper-Threading disabled by default but all that
is necessary in order to enable Hyper-Threading is the presence of a BIOS option
to control it. This is only for the workstation/server side of things, for the
desktop market there won't be any official mention of Hyper-Threading in the
near future although it may be possible for a motherboard manufacturer to enable
control via a special BIOS.

But the real question is why would Intel want to leave this
performance-enhancing feature disabled?


Check out the whole artical at www.anandtech.com



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