Can you Mix Different Capacity RAM Sticks?

simplymuzik3

macrumors 6502a
Original poster
Jan 29, 2009
589
0
I plan on getting the 8-core w/ the 2GBx4 upgrade from Apple, so that when I want to upgrade, I don't have to "throw away" all my 1GB Sticks. I also plan on ordering 2x4GB sticks and putting them in as well. This would mean 3 sticks/processor (2x@GB and 1x4GB). In the future, I wanted to buy 2 more 4GB sticks, or maybe 8GB sticks. Is it possible to mix/match RAM like this? What are the "rules" when buying RAM?

I just want to be sure because Im doing a BTO with the 4x2GB sticks from Apple.

Thanks,
 

Umbongo

macrumors 601
Sep 14, 2006
4,934
54
England
1Gb, 2GB and 4GB DIMMs should be able to be mixed. You may find some 4GB DIMMs don't work in a mixed environment, check with the manufacturer or where you are buying them from.

Apple only support unbuffered ECC with the Mac Pros so memory marketed for them will be of this type. 8GB DIMMs are all registered and so while they work (as any registered ECC DDR3 DIMM should) they can't be mixed with unbuffered memory.
 

simplymuzik3

macrumors 6502a
Original poster
Jan 29, 2009
589
0
1Gb, 2GB and 4GB DIMMs should be able to be mixed. You may find some 4GB DIMMs don't work in a mixed environment, check with the manufacturer or where you are buying them from.

Apple only support unbuffered ECC with the Mac Pros so memory marketed for them will be of this type. 8GB DIMMs are all registered and so while they work (as any registered ECC DDR3 DIMM should) they can't be mixed with unbuffered memory.
Is registered another way of saying "buffered" memory? I was looking around and most only talked about registered/non-registered. So any un-registered/un-buffered memory should be compatible with the RAM from Apple?

Sorry if that's a stupid question, Im a noob when it comes to memory:eek:
 

MacSince1985

macrumors 6502
Oct 18, 2009
319
210
If you just buy Mac Pro compatible memory you should be fine. Just wanted to note that 8GB DIMMs won't work with most Mac Pro certified/supported memory.
Here's OWC info regarding the 2009 models. I don't know how much applies to the 2010 line up.

Does "matched sets" mean "pairs"? or should all the modules match?

Also left to be seen is whether the 8Gb modules will work, raising RAM capacity to 64GB.
1066MHz ECC Mac Pro Memory Information
Up to 64GB of Total Memory
4 or 8 Total Slots
Apple Specified Thermal Sensor
DDR3 PC8500 ECC 1066MHZ
72 Bit (64 bit + 8 bit ECC)
High-Performance Multi-Channel
Apple Mac Pro "Nehalem" Models utilize high-performance Multi-Channel Memory addressing that benefits from the installation of matched memory sets. Memory upgrades are done using matched sets of same size modules.
 

Umbongo

macrumors 601
Sep 14, 2006
4,934
54
England
Matched sets should mean the modules are as identical as possible, this gives the best performance and most stability. What the real world out come of that is compared to, say, filling the memory slots with different capacity DIMMs from many different sources hasn't been shown as far as I know.
 
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