> Date:    Sun, 10 Jul 2005 17:45:09 -0700
> From:    Peter Shkabara <[log in to unmask]>
> Subject: Pentium Hyper-threading
>
> The more I learn the more I get confused. From Intel specs I
> find that the
> Pentium D is a dual core processor but does not support
> Hyper-threading. Is
> this because Intel has not yet created a dual core version
> that does include
> Hyper-threading, or is there something inherent to the design
> to preclude
> this?

Hyper-threading, to my knowledge, is a strategy to better
utilize cache architectures, i.e. share cache between
multiple executing applications. It's weakness appears to be
potential contentions between such applications.

This might help:

http://arstechnica.com/articles/paedia/cpu/hyperthreading.ars/5?12083

'Tis my understanding that dual core processors have independent L1
caches. Hence primary-cache contentions are not an issue.

> Another related question to pose. The Pentium itself can be
> thought of as a
> dual core 486.

This may not be a safe way of thinking. At least in the
context of counting instruction processors.

A single core Pentium has only one (uno) instruction processor
'tho it may have, say, multiple integer and/or float-point
pipelines.

>Does this mean that the Pentium D is really
> something similar
> to a quad core 486? (I do realize that the Pentium core has a lot of
> improved technology over the 486)

Well, no.

A dual-core die has 2 instruction processors, each with it's own
(at least L1) cache architecture.

This might help:

http://en.wikipedia.org/wiki/Dual-core

Hyper-threading *may* be looked back upon someday as an
interesting idea that became superceded by dual-core
architectures.

Hope this helps a little.

  Cheers,
  David

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