[geeks] Windows XP 64bit Licensing?

[nate at portents.com]

>> > Linux has no problem with >3GB of RAM.
>>
>> That depends on what you mean by "no problem"...
>
> I've run 32bit Linux on boxes with >3 gigs of RAM w/o problems.
>
> At $JOB-1, we had 4 big Dell boxes (6850s?) running RHAS 3 with a 32 bit
> load of the OS, each box had at least 4 gigs of RAM in them, I don't
> recall the total, but we were running Dell/Oracle/RH's recommended
> config for an Oracle RAC setup.

Well yeah you can put as much physical RAM as you like in a 32-bit x86
system, but that doesn't mean you'll get to see or use all 4GB.  How much
you get out of the 4GB (or more) is going to depend on your BIOS and what
video card you use.

You'll find that that the BIOS/chipset in most PCs will map the 32-bit I/O
memory space at right around the 3GB mark (and if you're unlucky the BIOS
will also do this in 64-bit!)  So you can have 4GB of physical RAM in
there, but once you get into your 32-bit OS it won't all be available to
the OS.

The only exception I've seen in on a dual socket 940 Opteron I put
together running Windows 2003 Server 32-bit, where because of the NUMA
architecture when I put 2GB of RAM off of one CPU and 2GB off the other
CPU, a total of 4GB was available in the OS.  If all 4GB was off of one
CPU, 3GB was available to the OS.

I run 8GB of RAM in one of my (non-NUMA) home PCs, and if I ran 32-bit
Windows it would only get to use 3GB.

- Nate