Dual 2 GHz PowerPC G5 beachballing and then freezing at random intervals

Question

My computer at work has been beachballing and then freezing at random intervals for the past week or so.
What happens is that all processes stop. The cursor is still responsive for a while, and then the application I'm in, regardless of what it is, “beachballs.”
Occasionally I'm able to wait it out and the computer becomes usable again and other times it just freezes. Then I can't force quit so I have to do a hard power cycle and then start up again. This happens every day, at least 4 times a day.
I've been keeping the system.log open to look for any tell-tale issues and noticed that during every crash I get the following information:
3 kernel[0] disk)s3: data underrun
3 kernel[0]
and it repeats until the computer becomes responsive again or I decide to do a hard power cycle.
In addition, I checked the System Profiler diagnostics area and found this:
 Last Run:    11/8/10 1:05 PM
  Result:    Failed
  Failure type:    Memory
  Memory slots:    DIMM6/J43, DIMM7/J44
So…I switched out the offending bars and switched them for 1 GB bars and this problem was solved.
The diagnostics result for the Power On Self-Test:
Last Run: 11/10/10 6:21 PM
Result: Passed
However…I'm still experiencing beachballing and freezing problems with the same severity and frequency.
Help!

Answer 1

gridout1959 wrote:
So, to clarify: do you suggest I use Disk Utility first to see if any problems are uncovered? Or should I use TechTool Deluxe instead and test the RAM with Memtest?
My two cents would be use Disk Utility first. If you don't have the install disk handy, you can do the same thing with single-user mode. See this link for details: http://support.apple.com/kb/TS1417
You have to run it from single user mode (start with command-S keys held down until you get a Unix terminal screen.
You can also run memtest from single-user mode, though I do not remember the command syntax offhand. Looking at an AppleJack log, though, I see the following command line entry that was used to run memtest on a three-pass check
*/usr/local/sbin/memtest all 3 -L*
Running memtest from single-user mode tests more of the RAM because little is occupied by the BSD kernel.
A snip of the terminal output running memtest:
Test sequence 1 of 3:
Stuck Address : ok
Random Value : ok
Compare XOR : ok
Compare SUB : ok
Compare MUL : ok
Compare DIV : ok
Compare OR : ok
Compare AND : ok
Sequential Increment: ok
Solid Bits : ok
Block Sequential : ok
Checkerboard : ok
Bit Spread : ok
Bit Flip : ok
Walking Ones : ok
Walking Zeroes : ok
Somewhat thorough, though no test is completely bulletproof.