[Novalug] 64bit vs 32bit

[Jon LaBadie]

On Sun, Apr 13, 2008 at 09:27:58PM -0400, James Ewing Cottrell 3rd wrote:
> Ken Kauffman wrote:
> >This isn't 100% true.  If you do a tremendous amount of multitasking, 
> >you may need more RAM than 4Gb.  So you'll need 64 bit to take 
> >advantage of all the memory above 3.5 Gb.  For instance, I run 8Gb on 
> >my desktop for multitasking reasons.
> >
> >Also, keep in mind that Linux will leave applications in memory even 
> >after they are closed -- unless -- it's "released" and another process 
> >needs to claim that space.  So you'll get a "virtual" speed up of 
> >frequently used programs if you open/close a lot but do not multitask 
> >as much.
> >
> >Ken
>
> None of my computers will hold more than 2G anyway. I have 2 slots using 
> DDR memory.
> 
> Now (some) 32-bit processors and Linux have the PAE extension, which 
> IIRC is intended for managing more than 4G.
> 
> So I'm not sure that 64 bits are required. Anyone else want to comment?
> 
> JIM
> 

There is a difference between what the system will support
in terms of total memory and what any single process can
address.  I've not seen a 32-bit system allow more than
3.5G for a single process.  Some are even lower.

An example is one client I had in NJ.  They knew their
applications were large and outfitted several workstations
with 10GB of RAM and tons of swap.  They were doing integrated
circuit design.  Things worked fine as they worked on pieces
of the chip design.  Then near the end of the design, when
they had to run some analyses that took 24+ hrs, it would
crash after 10-16 hrs when it ran out of memory.  Not system
memory, but the single process tried to allocate memory beyond
its 3 or 3.5GB limit.

No amount of RAM or swap would help them.  They ended up
getting a 64-bit compute server just for the big jobs.

-- 
Jon H. LaBadie                  jon at jgcomp.com
 JG Computing
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