[geeks] Windows XP 64bit Licensing?

[Charles Shannon Hendrix]

nate at portents.com wrote:
>>>> 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.

That's interesting, because so far every system I've built with >2GB of RAM has 
seen all of it just fine.

The only real issue is which memory model to pick.  Linux gives you the option 
of limited but faster memory mappings when you compile it.

> 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.

What difference does that make?  Ugly, sure... but on a virtual address system 
like Linux does it matter?

There are a lot of holes in the physical memory map besides where I/O resides. 
It's the job of the VM system to work around them.

All memory in Linux is virtual addresses and any given physical address can be 
marked off limits for paging VM.

In fact, being able to do that is a requirement on almost any architecture, 
since nearly all of them have a few holes in the physical address map.

What specific problem have you seen?

> 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.

I can't speak for Windows, but I've used Linux with 4GB and it was fine.

I think you are talking about a common default which is a 1GB/3GB kernel and 
userland split.

A lot of times this is an advantage.

It doesn't mean you don't have access to all 4GB, it just means no single 
process can access more than 3GB.

That's probably the model that Windows defaults to.


-- 
shannon           | An Irishman is never drunk as long as he can hold onto
                   | one blade of grass and not fall off the face of the earth.