[ale] Max RAM?

[JK]

Greg Freemyer wrote:

> All,
> 
> I need to buy a server in the next several months that may need a lot of RAM.
> 
> I thought x86 machines had a limit of 4GB, but then I see the HP
> ProLiant DL380 can have up to 32GB max.
> 
> Does the CPU model effect it?  AMD? Intel? Xeon? Pentium 4?
> 
> Can someone explain what the restrictions are, or point me at a good url.

Intel added a hack called "Physical Addressing Extensions" to
later Pentium models.  This hack allows the processor
to address up to 64GB of RAM via bank-switching, though
only 4GB is visible at any particular time.

Here's a M$ page about PAE support for Windows:

http://support.microsoft.com/kb/268363

Linux also supports PAE (as of kernel 2.4 at least),
and can address all 64GB of physical RAM, if
it's present.  The virtual address space for any particular
process, however, is still limited to 3GB (Linux
reserves 1GB [normally] of virtual space for the kernel).

-- JK