Red Hat EL5.0 is detecting only 3GB though physical is 16gb
 

Red Hat 5.0(32bit) is detecting only 3GB RAM

On server 16GB Ram is there and 64bit HW architecutre is there but Red Hat 5.0 [32 bit] is able to detect 3gb,

Can u give me some idea why?

To directly address more than 4GB of RAM, you need 64-bit hardware AND software. There is a mechanism to get around this---PAE---but I don't know much about it.
....but Google does:
http://www.google.com/search?q=pae+l...S177US235&aq=t

The more direct approach is to install the 64-bit version of your favorite OS.

What Pix referenced above is correct, I think the kernel option is something like "big memory support" or "big ram support" in the kernel config. It's not part of the default config on most distributions however so likely you'll need to compile it in (if you want 32b linux). Better method as stated by others is to use 64b linux.

Right, you likely want RHEL 5 x86_64. See this related thread.

Hi,

All above suggestions are correct. But for quick fix you can just enable SMP support. That means that you need to make sure that during boot-up the SMP kernel is loaded.Sample output below shows that SMP kernel is loaded on a 32bit OS.

Linux hostname 2.6.9-67.0.4.ELsmp #1 SMP Fri Jan 18 05:00:58 EST 2008 i686 i686 i386 GNU/Linux.

Mike --
Registered Linux User # 365113