[ubuntu-uk] Ubuntu Servers

[Tony Travis]

Chris Rowson wrote:
> [...]
> I've always used 32bit edition on servers myself. I've heard horror 
> stories about perl scripts using twice as much memory under 64bit etc, 
> etc.... I've never tested PAE with more than 4GB of RAM - I had heard 
> about the single process limitation, but as I only had 4GB to play with, 
> I've never had the opportunity to hit that limit!

Hello, Chris.

In fact you can only alloc() 2GB in a contiguous block if you have 4GB 
RAM installed. You can get somewhere near 3GB in total per process if 
you don't care about memory fragmentation with 4GB RAM installed.

Things improve quite a lot with 8GB installed, but you still can't get 
 >4GB per process using PAE. For many programs that's not a problem, and 
you're right about 64-bit doubling the size of memory usage in certain 
situations. Actually, I don't think 64-bit is worth it unless you have 
very BIG memory problems to solve. PAE is quite good if you want to run 
multiple instances of programs that have < 4GB memory footprints.

Bye,

	Tony.
-- 
Dr. A.J.Travis, University of Aberdeen, Rowett Institute of Nutrition
and Health, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, Scotland, UK
tel +44(0)1224 712751, fax +44(0)1224 716687, http://www.rowett.ac.uk
mailto:a.travis at abdn.ac.uk, http://bioinformatics.rri.sari.ac.uk/~ajt