[BWSchultz]

A long time ago on this forum, I read that you are supposed to install the largest RAM chips on the 'inside' of the slots in the G5. I have a G5 with 8 slots and this is what I had before.

empty
empty
256
512

512
256
empty
empty

The 512's are from Crucial and the 256's were installed by Apple. Same type of RAM.

This worked great for about 8 months. Two days ago, I had a kernel panic. I did the troubleshooting and determined it was the RAM causing the problem. So I put just the 256's in the inside slots. I restarted and it worked fine. Ok, great. Then, just out of curiosity, I put the big chips back in like this:

empty
empty
512
256

256
512
empty
empty

And to my shock and amazement, it worked! The G5 recognized all of the RAM and it's been running smoothly for 48 hours now.

So as best I can determine, the 512's work everywhere except the first two slots, which is where I thought they should be. So I guess this throws out the logic of putting the biggest chips on the inside. Any comments or similar findings?

[Detrius]

Sometimes, RAM just needs to be re-seated. It's the same with PCI cards, AGP cards, processors, etc... sometimes the connection is lost for one reason or another and you need to reseat the component.

With that said, either you have bad RAM or you don't. Either you have a bad logic board or you don't. Relying on whether or not your system crashes is NOT a reliable to test. You need to run an actual hardware test (hint, hint Apple Hardware Test that came with your machine).

What your are seeing can be a normal response to bad RAM. The logic board will use the memory that is closest first. The further away they RAM, the higher up in the address space the RAM modules are placed. If you have a bad stick of RAM on the inside, your Operating System gets corrupted quickly and your machine crashes. If you have a bad stick of RAM on the outside, only the data/software that is put in that RAM module gets corrupted. Run the Apple Hardware Test in multiple arrangements and see what you get.

Also, the idea that the bigger RAM modules should be closer to the processor (in the center on the G5) is a good idea in theory. In practice, it shouldn't make a single bit of difference. The bottom line is that it will not take extra cycles of the RAM clock for data to come from the outside modules. If it did, the system should be redesigned.