Re: [Sheflug] Physical memory

[Will Newton <xxxxx [at] xxxxxxxxxxxxxxxxxxxx>]

On Friday 13 Sep 2002 9:14 am, Etienne Prinsloo wrote:

> I am just wondering what is the maximum ammount of Physical memory
> (RAM) that a PC can handle.  I have heard that due to the 32bit
> architecture, PC's can't handle more than 2Gig's of RAM.
> Is this true?

No. PCs can only access 4Gb of contiguous address space, but if the OS can 
give a virtual address space to each process you can have more i.e. one 
process may only access 4Gb [approx.] of RAM, but there may be more than one 
process. This is called "HIGHMEM" in the kernel and needs to be enabled, and 
needs hardware support. My motherboard for example will only accept 3 x 
512Mb, 1.5Gb total RAM. HIGHMEM allows a maximum of 64Gb on hardware that 
supports it. I have no idea which hardware this is, I have never seen a 
motherboard that can do this, probably one of the Xeon boards. Also a process 
will not see exactly 4Gb of RAM, I believe 1Gb is always reserved for the 
kernel, and there may be other deductions.

> Is there a way that this limitation can be side-stepped?  (we have
> analysis runs that require more than 2Gigs, and therefore have to use,
> expensive, 64bit UNIX boxes)

I suspect you will need to buy expensive x86 hardware instead, the commodity 
stuff would not seem sufficient. I recommend you use the 64 bit UNIX boxes if 
you have them available. Preferably with Linux installed. :)
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