This may sound weird, but it's true ...
I bought my wife an iMac G5 with 1 512 MB memory stick. I also ordered another 512 MB stick (Crucial) from newegg.com. The Crucial memory I ordered was the same type I had ordered, and successfully installed, in my PM G5 2.5 DP.
So, the machine shows up, I put the Crucial memory in and I run the hardware test. Boom, memory failure. I pop out the Crucial memory, re-run the test and it passes. Bad memory from Crucial is unusual, but not out of the question, of course. However, there's this nagging bit in the back of my head wondering if there's some subtle difference between PM G5 memory and iMac G5 memory. I figured I'd go direct to Crucial and order specific iMac G5 memory. It shows up yesterday, I install it and the memory test fails again. Two bad sticks? Low probability. Bad memory slot? Maybe. I take the Crucial memory out and move the Apple memory from its original position in slot 2 and put it in slot 1. I re-run the memory test and it passes. The memory slot isn't bad. Now I put the direct-from-Crucial stick in memory slot 2 and damn if it *does* pass the memory test and boots the OS successfully! Now I'm really curious. I open 'er up again and replace the direct-from-Crucial stick with the newegg-Crucial stick, run the memory test again and, again, it passes.
Ok, so now I check to see if the memory sticks are pairing successfully and giving me a 128-bit memory path. No joy. 64-bit. I figure I'll try the two Crucial sticks, which have proven to be OK individually, with the expectation that they will pair (they turn out to have exactly the same model number on the stick). I pop out the Apple stick, put both Crucial sticks in and re-run the memory test. It fails!!! WTF! The *only* configuration that will run is Apple memory only or Apple memory in slot 1 and Crucial memory in slot 2, but the latter won't pair successfully. Not a happy camper.
Later in the evening it dawns on me that my PM G5 has 2 512 MB sticks of Apple memory and 2 sticks of the same Crucial memory I bought for the iMac G5. So, I take the 2 sticks of Apple memory out of the PM and put them in the iMac. I put the iMac Crucial memory in the PM in place of the Apple memory. I run extended memory tests on both machines and both tests pass. In addition, all the memory pairs successfully; the iMac is running with the full 128-bit memory path. Nirvana.
I certainly can't explain these perturbations; all the memory sticks pass the extended memory test. Go figure.
FS: Genuine Apple iMac G5 512 MB memory stick ($95 + shipping, US only)
I bought my wife an iMac G5 with 1 512 MB memory stick. I also ordered another 512 MB stick (Crucial) from newegg.com. The Crucial memory I ordered was the same type I had ordered, and successfully installed, in my PM G5 2.5 DP.
So, the machine shows up, I put the Crucial memory in and I run the hardware test. Boom, memory failure. I pop out the Crucial memory, re-run the test and it passes. Bad memory from Crucial is unusual, but not out of the question, of course. However, there's this nagging bit in the back of my head wondering if there's some subtle difference between PM G5 memory and iMac G5 memory. I figured I'd go direct to Crucial and order specific iMac G5 memory. It shows up yesterday, I install it and the memory test fails again. Two bad sticks? Low probability. Bad memory slot? Maybe. I take the Crucial memory out and move the Apple memory from its original position in slot 2 and put it in slot 1. I re-run the memory test and it passes. The memory slot isn't bad. Now I put the direct-from-Crucial stick in memory slot 2 and damn if it *does* pass the memory test and boots the OS successfully! Now I'm really curious. I open 'er up again and replace the direct-from-Crucial stick with the newegg-Crucial stick, run the memory test again and, again, it passes.
Ok, so now I check to see if the memory sticks are pairing successfully and giving me a 128-bit memory path. No joy. 64-bit. I figure I'll try the two Crucial sticks, which have proven to be OK individually, with the expectation that they will pair (they turn out to have exactly the same model number on the stick). I pop out the Apple stick, put both Crucial sticks in and re-run the memory test. It fails!!! WTF! The *only* configuration that will run is Apple memory only or Apple memory in slot 1 and Crucial memory in slot 2, but the latter won't pair successfully. Not a happy camper.
Later in the evening it dawns on me that my PM G5 has 2 512 MB sticks of Apple memory and 2 sticks of the same Crucial memory I bought for the iMac G5. So, I take the 2 sticks of Apple memory out of the PM and put them in the iMac. I put the iMac Crucial memory in the PM in place of the Apple memory. I run extended memory tests on both machines and both tests pass. In addition, all the memory pairs successfully; the iMac is running with the full 128-bit memory path. Nirvana.
I certainly can't explain these perturbations; all the memory sticks pass the extended memory test. Go figure.
FS: Genuine Apple iMac G5 512 MB memory stick ($95 + shipping, US only)