RAM not being recognized (Mac Pro)

[bloogersnigen]

I just purchased a Mac Pro. Its fabulous, does everything crazy fast, but will not recognize all of the RAM. I have run the hardware tests, and everything passed.
For further background info, the Mac Pro came with a standard 2 GB (2X1GB) and I bought 8 GB (4X2GB) from OWC for a total of 10 GB.

To simplify things, when I refer to slot 1, I mean the combined total of slot 1 in both RAM cards.

Here are some tests I've done.

Configured this way:
Slot 1: 2GB
Slot 2: 4GB
Slot 3: 4GB
Slot 4: 0GB
It recognizes 6 GB

Configured this way:
Slot 1: 4GB
Slot 2: 2GB
Slot 3: 4GB
Slot 4: 0GB
It recognizes 8 GB

Configured this way:
Slot 1: 2GB
Slot 2: 0GB
Slot 3: 4GB
Slot 4: 4GB
It recognizes 6 GB

I have come to the conclusion that the slots 2 and 4 are broken. Is there any other possibility?

 

[costabunny]

I have

Upper
1 - 1GB
2 - 1GB
3 - 4GB
4 - 4GB

Lower
1 - 4GB
2 - 4GB
3 - 0
4 - 0

This works fine (if you swap out the 4GB for 2GB you can see how your RAM would map to my setup). give it a try and see what it does?

 

[bloogersnigen]

Well first of al, I've been matching the pairs because I thought it makes a multi processor computer run faster, and secondly, my card is broken, there is good ram in there that is not being recognized.

 

[costabunny]

right I see

You are splitting the 2GB (1 +1) accross the cards?
(only as shipped 1GB + 1GB should they be split)

Put them on the same card (Mac Pro Banks are adjacent to one another, not accross the same slot on each card).

if you follow the setup I mention I am pretty sure it will work.

upper
1- ORIGA
2- ORIGB
3- NEWPAIR1-A
4- NEWPAIR1-B

lower
1-NEWPAIR2-A
2-NEWPAIR2-B
3-EMPTY
4-EMPTY

Apple Manual Guide for Mac Pro Memory will show you what I mean with colour coded diagrams :
http://manuals.info.apple.com/en_US/MacPro_Early2008_MemoryDIMM_DIY.pdf

 

[bloogersnigen]

That worked great. 10 GB of RAM showing. Thanks a ton, guess that serves me right for skimming through the manual. On another note, it took a really long time to start up after the RAM switch. Oh well, seems to be working perfectly now.

 

[costabunny]

you are welcome

It did seem a little odd to me at first (esp as I am used to the PC Mobo format of matching pairs).

don't know why it took longer to boot tho :S maybe it did a disk check or ram check or something. See if it boots ok next time and ignore it.