> Yes: The 32-bit kernel will leave 25% of your 4 GB RAM unused, I believe.

I'm running 32-bit SL6.0 on a 5gb-RAM machine and (unless I'm missing
something) it sees and uses all of it.

$ free
             total       used       free     shared    buffers     cached
Mem:       5061660    4934336     127324          0     199168    3129100
-/+ buffers/cache:    1606068    3455592
Swap:      4008056     853280    3154776
$ uname -a
Linux blossom.fujigreenwood.com 2.6.32-71.24.1.el6.i686 #1 SMP Fri Apr
8 01:07:04 CDT 2011 i686 i686 i386 GNU/Linux
$

This same machine saw the same memory under SL5.x using the PAE kernel
(AIUI all the SL6 kernels are PAE).

                                                         - Bluejay Adametz

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