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macrumors member
Original poster
Apr 30, 2013
Hi guys i have mac pro 2009 i am looking to upgrade my memory to 32gb 1333MHz DDR3 ECC Memory dimm and latter and down the road my cpu but i usually do 3d modeling with lots of fire sims ect is there a difference between dimm or udimm



macrumors 68030
Jan 3, 2014
Silicon Valley, CA
UDIMM is Unbuffered RAM, which is a subtype of DIMM (Dual Inline Memory Module.) Unbuffered RAM modules directly expose all electrical chip signals to the bus. Registered RAM has signals buffered by intermediary components.
All Mac Pros use ECC RAMs. From what I have read, Mac Pro 2009 was the first to support unbuffered ECC RAM - e.g. UDIMMs.
More here:


macrumors P6
Apr 3, 2014
Hong Kong
UDIMM is a sub set of DIMM. In other words. if you buy UDIMM, you are actually buying DIMM. However, if you buy DIMM, you may be buying UDIMM, or RDIMM....

So, your questions is quite meaningless.

For 4,1, you can use either UDIMM or RDIMM, but CANNOT mix them together. In general, single RDIMM can has bigger size (e.g. a single 16G RAM stick), which UDIMM may not have.

So, if you want to go for large size memory, RDIMM usually is a better choice. Otherwise, UDIMM is fine.


macrumors member
Apr 22, 2015
udimm are non-ecc. This is normal desktop ram. It tends to be cheaper then ECC. (10600U-PC3 ram)

ECC is what the 4,1 or 5,1 mac pro came with originally. It is slightly slower and also more expensive then Udimms but it also protects you from bit flips due to cosmic rays which helps system stability. ECC is rare in sizes above 4gb chips, 8gb are the biggest chips available. (10600E-PC3)

Registered is the cheapest, it comes from server pulls. It is also ECC and thus slightly slower but more stable. It is available in the biggest sizes possible, 16gb. (10600R-PC3)


macrumors P6
Feb 8, 2003
The Peninsula
udimm are non-ecc.
Incorrect. UDIMM are unbuffered - they can be either ECC or non-ECC. Buffered and ECC are independent.


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