Hello all.

I'm having a problem with my new Mac Pro memory. Let me explain:

I sent away for 4 gigs Crucial RAM for my new Mac Pro. That's two 2 gig chips.

I ordered the computer with 1 gig RAM. The 1 gig was in the form of two 512 chips, as FBDIMM needs to be installed in symmetrical pairs.

I just installed the new RAM, and put the new chips on the riser which was totally empty.
So now, I have one riser (memory board) with the original two 512 chips, and one riser with the two 2 gig chips.

I turned on the comp, and everything worked fine. I checked System Profiler and saw, however, that only the two NEW chips were being recognized. The original two, which had been working fine, and which I didn't touch, are no longer being recognized by the computer.

Why is this?

Does it have to do with this? http://docs.info.apple.com/article.html?artnum=304492
I think not. I don't have my memory installed symmetrically (because I can't given the particular assortment of chips I have, right?), but the article merely says that I "may not achieve the same performance levels as when DIMM pairs are installed on both risers evenly." It doesn't say that some of the RAM won't be recognized.

I'm sorry if this is too longwinded; I wanted to give as much info as you may need to help me, if help me you can.

Thank you so much in advance.

I know this forum better than that...I know someone here knows about this kind of stuff. :) Please?

First you need to narrow the problem?

Put the old memory back in it's original position. Restart.
If all is well put the new memory on the same riser. Restart.
If all the memory shows up this time then on the next purchase be sure to put matching memory in the lower riser.

Mac pretty clearly states that paired memory (different risers) needs to be the same size and maker.

Sounds like only the new stuff will work because it is paired. I don't think it is compatible with the 512's.

Check to see if the riser was seated firmly into the logic board and make sure the arrangement of paired DIMMS is correct.

Follow the directions in this PDF:

http://manuals.info.apple.com/en/MacPro_MemoryDIMM_DIY.pdf

DIMMS belonging to different paired sets need not be paired.

I think that article says it all.

The pair in riser A need to match the pair in riser B = old + new won't work.

You cannot have either 1 or 3 on a riser = can't split the old set/ new set, ergo, old + new won't work.

To coin a well known phrase or saying = you're sc*$#ed!

I'd buy another set of 2 X 2 gigs and sell the 512's on DVinfo (or e - bay).

I'd say "the system" is smart enough to pick the biggest hunk on the beach and kick sand in the runts face, you're 512's are doomed.


CS

I'm sorry but I must respectfully disagree with Chris. Matched pairs need only be within the paired set on each riser as illustrated by the link in my prior post. It is not necessary to span pairs across the risers. Optimum performance aside, the RAM should still be visible using System Profiler.

Your "respectfuly disagree" is noted and most possibly unwarranted, as from the diagram I (as per effing usual) did NOT peruse before I posted, you are, of course, absolutely correct.

I stand corrected. Mea Culpa.

CS

Thank you all, but I dont think you really read my post or the Apple instructions (with the exception of Tim, thank you, and Chris, later).

The memory needs to be in matched pairs. It is. I have 2 two gig chips on one riser, and two 512 chips on the other riser. That's matched. They should work, and they should show up, as I understand it.

Rick: I didn't touch the old RAM, so I cant put it back in its old position.

Tim: Thank you, I will do just that. Hope it works.

Thank you all for your responses.

Any other help?