Macpro reads RAM incorrectly

[sonny7]

I have a mac pro quad core (from 2007), 10.4.10 OS. I have 4 gigs of ram, 4 i gig sticks. I noticed that sometimes my computer will read only 3 gigs instead of 4, 2 one gig sticks, and 2 512 sticks.
The Ram is seated correctly.
To correct the problem I took the ram sticks out and "rearranged" them, top to bottom and vice versa then the computer read it as 4 one stick gigs. It only happened one time (so far in the middle of a session).

Any one else have this issue. The ram came with the computer and my nearest mac repair shop is some distance.

Could this just be a one time occurance???


Thanks

[BRH]

I had the same thing happen with a 2008 8-core machine. Did the same thing and switched the RAM around. That helped. I think it's a mac thing.

[docbop]

The Mac Pro's are very picky on how your RAM is laid out across the two riser boards. The Apple technote is sparse on the topic. OWC who sells a lot of Mac RAM has a tech note of their own that has more details.

www.macsales.com