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I have a machine running CentOS 4 32-bit with 12 gigs of RAM.

If I run the free command I see:

# free
             total       used       free     shared    buffers     cached
Mem:      12409180    2227676   10181504          0      48544     961296
-/+ buffers/cache:    1217836   11191344
Swap:      4192956          0    4192956

If I run top I see that we have 12 gigs of RAM.

The question is I am running kernel 2.6.9-78.0.22.ELsmp and I was wondering if the system is able to use more than 4 gigs of RAM. I have seen many things saying you need to have this kernel version (PAE) or you need the smp kernel version. I understand in a 32-bit OS that the RAM is limited per process, but I was wondering if the OS can address more than 4 gigs for application use (as in 5 applications using 2 gigs of ram each).

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On 32bit processor as I know, more than 4G RAM cannot be allocated to one process –  Ency Jan 21 '11 at 17:23
I may have not worded the question properly, but I was wondering if I have multiple processes running on the server, if they can use up to 4 gig limit (5 processes using 2 gigs of ram each). –  jinanwow Jan 21 '11 at 17:33
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3 Answers

up vote 3 down vote accepted

The space for each process is still strictly restricted to 4GB even with PAE, but multiple processes can be run.

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Yes. You have 12 gigabytes enabled for your kernel, and you can use multiple processes with 2 gigabytes of memory each.

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Assuming PAE is in use so access above the 4GB line is possible, each process will be given 4GB of virtual-memory space to play with. They can and do use memory above the 4GB line, it's just at a higher latency than RAM below the 4GB line.

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