[CentOS] Adding RAM

Morten Torstensen morten at mortent.org
Sun Dec 7 19:37:46 UTC 2008

Kevin Krieser wrote:

> At least with regard to the upstream provider, on X86 the desktop  
> version has a limit of 4GB of RAM, regardless of how much more memory  
> you have.  And they removed the hugemem version, so instead of up to  
> 64GB of RAM on 32 bit, you can only get to 16GB for server versions.

With PAE you can access up to 64GB memory. It works much the same way as 
XMS memory in DOS, where "high mem" is mapped to a low mem window. It is 
just addresses that are mapped, there is no physical copying of memory 
that you had with EMS memory.

Generally, PAE would not make much sense on >16GB memory machines, as 
you still need the space in the 4GB range to address it. Personally I 
would use PAE on machines with up to 8-12GB memory (assuming x86_64 
wasn't an option). With more than 16GB I would recommend against it, as 
you get a lot of remapping and/or limited space in the 4GB range.

YMMV depending on specific workload of course.


//Morten Torstensen
//Email: morten at mortent.org
//IM: morten.torstensen at gmail.com

I can't listen to that much Wagner. I start getting the urge to conquer 
	-- Woody Allen

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