Hi,

I have a Mac Pro with DDR2 667 FB-DIMMs.  Presently I have two pair of 512MB modules = 2GB.  There are four more slots available (two slots on each of the two risers/boards).

I would like to purchase a pair of 2GB modules = 4GB.

I've always heard that with DDR memory, it must be symmetric, but I presume that relates to the pairs of modules, and not to the total number of pairs.
Will it be a problem (or will it increase latency!) to install these two extra modules for a total of 6GB, leaving two open slots?

Thanks in advance.

So you have 8 slots?





For maximum memory/type/speed, etc. check the motherboard manual, we can't tell you without a model number.





As for that symmetry thing, it is known as "dual channel" and only affects overall memory system performance and is not necessary for system functionality.



http://en.wikipedia.org/wiki/Dual-channel_architecture