MacPro showing 3GB of 12GB installed on Snow Leopard

Personally, I'd just reinstall Snow Leopard. Reinstalling Snow Leopard over Snow Leopard will leave all your files intact and only replace the system files.

~Lyssa

Hi Tim,

it sound like you have a real work horse of a machine.

you could try a safeboot http://support.apple.com/kb/ht1455
just booting ones into safe mode can fix lots of different issues
while in safe mode, check system profiler, see if it sees all the ram
reboot, see if it still sees all your ram

re-installing the os can resolve lots of issues. And like pointed out, 10.6 doesn't erase your computer when you re-install the os.

Message was edited by: TeenTitan

Usually just one pair of DIMMs will report half their size, yours seems like something I'd first do an SMC Reset.

Marginal RAM and seems like last summer we (Mac Pro owners and forum) saw quite a few.

Your Mac uses FBDIMMs. They run hot, so much so that Apple recommends waiting 10-15 minutes after shutdown BEFORE opening the side door to prevent sudden changes in air temperature. And many users boost the fans just 300-400 rpm to allow more air flow and prevent the temps from rising - the SMC can wait too long to kick in and easier to prevent in the first place.

Someone else had almost identical situation, on this forum (and not in Mac Pro section for Previous to 2009). So actually the first time I've seen someone say it was OS related. What can happen is in a RAM situation like yours, marginal RAM is causing the system to "go bad" and require reinstall due to writing data. Parity errors can also end up with corrupt files. A good reason to do preventative maintenance on a weekly basis with Disk Warrior.

No one recommended Apple Hardware Test?

So you never have to do a fresh install, now is the time to clone your good system - to a sparse disk image; to a backup drive partition.