When you are adding RAM to a computer, does it really matter if the sticks have unequal amounts of memory or do you always need them to have equal amounts of memory? Today’s SuperUser Q&A post has the answers to a curious reader’s questions.
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.
Photo courtesy of redjar (Flickr).
The Question
SuperUser reader LanceLafontaine wants to know if using unequal amounts of RAM really does decrease performance:
Does using unequal amounts of RAM cause a decrease in performance or is it just a myth?
Additional Notes: For best performance, fill both memory slots, installing an equal memory module in each slot.
This is not the first time that I have heard of this phenomenon, and it is definitely not specific to Apple. Why is this the case? Other than the obvious decrease in available memory, why would it be worse to run with 6 GB (14 GB plus 12 GB) than with 8 GB (2*4 GB)?
The Answer
SuperUser contributors David Schwartz and x have the answer for us. First up, David Schwartz:
Followed by the answer from mVincent:
With uneven amounts, memory cannot be interleaved and has to be mapped first to one stick and then the other. A program that is accessing a large contiguous chunk of memory will find almost all of its access going to one stick and there will be no bandwidth combination.
Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
Why is this the case? Other than the obvious decrease in available memory, why would it be worse to run with 6 GB (14 GB plus 12 GB) than with 8 GB (2*4 GB)?
When two non-identical memory modules are used, the motherboard will run the memory modules at the speed of slowest module.
