What version of RHEL are you using? If you aren't running a current 64-bit system, such as an older 32-bit system with extended memory support, then you may be limited to 32GB. IE, install a current RHEL (or clone such as CentOS) x86_64 version. The 64-bit OS can handle both 64-bit as well as 32-bit software, so you should be ok as far as running legacy code is concerned, though occasionally there may be shared library issues.
rubberman
Posting Maven
2,571 posts since Mar 2010
Reputation Points: 365
Solved Threads: 305
Skill Endorsements: 52
There may be a BIOS configuration issue, or the memory is not properly installed. RHEL 6 should see all of the RAM without problems.
rubberman
Posting Maven
2,571 posts since Mar 2010
Reputation Points: 365
Solved Threads: 305
Skill Endorsements: 52