[UFO Chicago] >4G ram/64 bit OS

[Jesse Becker]

--- On Sun, 11/22/09, Politik Durden <politikdurden at yahoo.com> wrote:
> If a motherboard takes more than 4G of ram, say it takes 8,
> I would need a 64 bit OS to use all 8 G of ram ? And if I
> use a 32 bit OS, the OS would only be able to see the first
> 4G of ram on the board ? 

Depends on the OS.  If the OS really *is* purely 32bit, period, end of story, then I think you are correct.  There are some hardware tricks (PAE is one), that allow 32bit hardware to use more than 4GB of RAM.  This obviously requires OS support.  There's a good table here:

http://en.wikipedia.org/wiki/Physical_Address_Extension

However, there are some additional issues.  Even if you have an OS that supports PAE, but you are running on 32bit hardware, there are still some limits.  Linux, on 32bit systems, limits the amount of RAM for a *single process* to between 3 and 3.5GB (depending on the kernel and various patches).  This is a hard limit.  So even if you have 64GB of RAM installed on a 32bit box, most of it will be unused unless you can run multiple processes (which may or may not be an issue for you).

True 64bit hardware, running a 64bit OS will not have this limit.

--
Jesse Becker
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