At 20:27 08-05-98 -0400, HG wrote:
>The Pro can cache up to 4GB (I think!), while the PII can cache up to
>512MB in single config, and up to 1GB in dual processor config. I got this
>info off of http://www.anandtech.com, but don't quote me on it. TTYL


According to page 1-1 of the Pentium II Processor Developer's Manual:
"Memory is cacheable for up to 512 MB of addressable memory space, allowing
significant headroom for business desktop systems."

According to "Pentium Pro Processor System Architecture" (MindShare, Inc.),
the Pentium Pro L2 cache can handle 36-bit physical memory addresses. (It
can handle the full 64 GB physical memory space!) Increasing the L2 from
256 KB to 512 KB (or 1 MB) doubles (or quadruples) the depth of the
cache lines but does not change the Tag size or the L2's four way
set-associative implementation.

(The PPro manuals and datasheets make no mention of L2 cache addressing
limitations, leading me to feel confident that the MindShare book is
correct.)

Summary: The PII caches 512 MB of addressable RAM, but the PPro caches the
full 64 GB physical address space. (See my previous message for the reason
why this is *sixteen* times 4 gigabytes.) The PPro also does Error Checking
and Correction (ECC) in both L1 and L2 caches, whereas the ordinary PII
only does ECC in the L1 cache. And of course the L2 of the PPro operates
at the full clock rate of the processor, whereas the L2 of the PII operates
at half the processor's clock. A pity that the PPro did not become more
popular.

Regards,
Bill