RAM not recognized: how to restore
Reseating, resetting PRAM can help.
[Friday, May 16th]
Several users have reported an issue in which, upon installing additional RAM to the Mac Pro, the computer does not recognize the total amount of RAM installed. This problem persists even after putting the RAM in various slot configurations. As stated by a MacFixIt forums user:
"I'm having trouble with my RAM upgrade. I just bought a new 2.8 dual quad core MacPro with 2GB of RAM (2x1GB). I bought an additional 4GB RAM (2x2GB) from TransIntl. However, the most my Mac will see is 4GB, no matter how I configure the RAM."
For this user the only RAM that was recognized in the system profiler was the original 2GB RAM, even though the system said there was 4GB total out of the 6GB he had installed.
A user on the Apple discussion boards found that after successfully installing new RAM, he suddenly lost one GB:
"They both arrived the same day so I installed the RAM before I even started the computer for the first time. I checked the "About this Mac" after start up to make sure the RAM was all seen and it showed 4GB 800 MHz DDR2 FB-DIMM. Today I was showing off the machine and opened up the specs and suddenly I see 3 GB of RAM. Inside System Profiler it shows two of my sticks as 512MB. What happened?"
Fixes: The first thing one should do is ensure the RAM risers and the individual RAM sticks are properly seated, and that the RAM is installed in matched pairs, following Apple's instructions. Firmly press them down into the riser cards and give them a slight wiggle to ensure they're seated all the way down. Be sure you are properly grounded so as not to harm the RAM with static electricity discharges.
Once the RAM is properly installed, reset the PRAM on the computer. Do this by booting up while holding down the options-command-P-R keys all at once until you hear a second set of boot chimes, then release the keys and allow the computer to boot normally. The PRAM contains some RAM-related firmware variables that could present RAM incorrectly if not properly configured; resetting the PRAM will clear these variables and allow the RAM to register properly.
Feedback? Late-breakers@macfixit.com.
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