64-bit vs 32-bit

Freddie Cash fcash-ml at sd73.bc.ca
Wed Aug 2 21:04:23 BST 2006

On Wed, August 2, 2006 12:02 pm, Thomas Sperre wrote:
> Onsdag 02 august 2006 00:47, skrev Freddie Cash:
>> The only real benefit to running a 64-bit OS is to gain access to
>> more memory.  If you don't need more than 4 GB of RAM, then there's
>> really no big incentive to run a 64-bit OS.
>> ----
> A 32-bit system one process can adress approx 2 Gb. If you have
> processes that could require more than 2 Gb of memery, 64 bit is the
> only way.  Thus, 64-bit has advantages starting from 2 Gb of memory
> requirement/process rather than 4 Gb. Advantaves is perhaps a bit
> subtle wording as I guess 64 bit makes something possible that is
> impossible with 32 bit.

Actually, it's 3 GB on all the 32-bit OSes out there (I believe, I
know for sure with FreeBSD, Linux distros, Windows 2000+, OpenBSD). 
You just have to pass a kernel or boot option to tell the OS to use a
3/1 split between userspace and kernel memory.

With a PAE-enabled kernel, you can use up to (I think) 16 GB of RAM
(might be only 12 GB), with each userland process having access to 4
GB (max) each.

So, the only real advantage for 64-bit CPUs and OSes is to access more
than 4 GB of RAM (I believe the Opteron UP and 4-way SMP motherboards
can go up to 64 GB right now, but I could be wrong on that ... our
current 2-way SMP boards go up to 16 GB).

> I guess the applications as well as the OS has to be 64 bit for this
> to work.

Correct, I believe.  Running a 32-bit application on a 64-bit OS will
still limit that application to 4 GB of RAM.  But, you can run
multiple 32-bit apps on a 64-bit with each one having its own 4 GB
memory space to use, without swapping.  :)

Freddie Cash, LPCI-1 CCNT CCLP        Helpdesk / Network Support Tech.
School District 73                    (250) 377-HELP [377-4357]
fcash-ml at sd73.bc.ca

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