On Jul 19, 2009, at 12:51 AM, Clark Martin wrote:

> Pop all but one RAM stick and boot from the CD/DVD.

Dual G5's use matched pairs, you can't boot with a single stick. This  
complicates checking RAM and slots. Also, determining which slots are  
"pairs" required a chart, the representation in System Profiler does  
NOT match the physical pairs. As I recall, the two banks are mirror  
images with pairs starting with the innermost and moving to the  
outermost slots.

My G5 has required me to reseat the RAM many times before finding a  
combination where all sticks are fully recognized, and this is with  
100% good RAM. My experience with a single PC that uses matched pairs  
was even worse, I reseated the RAM 23 times before it worked. This was  
a PC with only two slots, so it took 23 reseats to get it to boot at  
all, but once it booted, it's been fine for over a year. My G5 has  
eight slots, fully populated, and it took probably 15 tries to get all  
the RAM working together, but I NEVER had a situation like described  
in this case - mine always booted normally, but one pair or another  
failed to be recognized. I assume that once you get 240-pins per  
stick, if only 1 pin out of 480 fails to make a clean contact, that  
pair doesn't work. It took some time.

In both the G5 and PC, once the RAM was fully recognized, I've had  
zero problems.

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