At 19:03 07-05-98 -0400, Michael wrote:
>I heard something today from a supposedly reputable and knowledgeable
>source that frankly I am having trouble believing...
>According to my source, there is a little known limitation with current
>Pentium II processors that allow them to recognize or address a limit of
>64Megs of RAM.

Your friend is wrong. Maybe he is confusing this with the 64 MB cache
limitation of *Pentium* motherboards that used the 430FX, VX, and TX
Intel chipsets.

The Pentium II with it's on-module L2 can cache up to 512 MB of addressable
memory. (This is from the Pebtium II Processor at 233 MHZ, 266 MHZ,300 MHZ,
AND 333 MHZ Data Sheet" and also the Pentium II Manual.)

Like the Pentium and Pentium Pro, the Pentium II can address up to 4 GB
of physical Memory (and can address up to 4 TB of virtual memory, a TB
being a thousand GB).

   Actually, the amount of RAM addressable by the Pentium Pro and Pentium II
   can be 64 GB. By paging the physical RAM and enabling the PAE (physical
   address extension) flag in control register CR4, bit 5, 4 additional
   address lines are enabled. This allows for 36-bit physical addresses,
   not just the 32-bit addressing which gives 4 GB. (2**32 Bytes = 4 GBytes
   whereas 2**36 Bytes = 64 GBytes.)

Someone else on the list said that 512 Kb of L2 can only cache 64 MB of RAM.
This is wrong. The amount of addressable memory that can be cached depends
on the size of the TagRAM, not the total amount of cache memory. (L2 is
composed of the TagRAM and burst pipeline synchronous static RAM (BSRAM)
memories. The amount of TagRAM used on both the Pentium Pro and Pentium II
processors is sufficient to allow 512 MB to be cached. This could
conceivably be increased by using larger TagRAM. (The total sizes of L2
offered with different Pentium Pro and Pentium II processors varies from
256 KB up past 1 MB. The prices for these specialized Pentium Pro and
Pentium II processors is very high.)

Regards,
Bill