Q: adding memory to a late 2013 mac pro
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Sep 27, 2014 7:58 PMby Grant Bennet-Alder,HelpfulThere is very little hard information about mixing modules and leaving slots open. But the fact that Apple ships a configuration with three modules says you can.
8GB and smaller modules can be mixed. Use of pairs is said to produce some extremely small speedups, probably not measurable using regular software.
16GB modules are Registered modules and cannot be mixed with smaller sizes.
These folks will sell you modules by the each if you desire that:
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Sep 28, 2014 7:56 AMby Grant Bennet-Alder,There is nothing specific in that document or the linked memory specification that precludes the mixing of sizes or leaving slots open. There is only one line that touches on those issues at all:
- Use the same size memory modules across all slots to maximize performance.
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Sep 28, 2014 1:29 PMby Grant Bennet-Alder,OWC HAS done some experiments using test with different sizes of modules, and they are described in this blog:
http://blog.macsales.com/22745-mix-and-match-more-memory-faster-mac-pro-2
Their main conclusion was that the differences between optimum and non-optimum resulted in real-world speed differences of about 3.5 percent.
On the previous generation (big Silver Tower) Mac Pro, results under 5 percent were considered completely negligible, and speed differences under about 15 percent could be justified by different factors (such as the enormous initial cost of the optimum modules).
OWC has a buy-back program for your used DIMMs. It makes their slightly higher prices for new DIMMs about even with Vendors that do not offer a buy back. As always, deal with a Mac-Centric vendor who states:
"It works in your Mac,
or your money Back."
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Sep 28, 2014 9:00 PMby louiewu,I Know about the memory suppliers, but what i want to know is can i buy two 8 gb modules now and put them in and later on down the road buy the other two moudles and put them in. I would also like to know if i can do this with 16 gb modules as long as all of the modules sizes and types ( ie registered or un registered ) matched. Do the LOT NUMBERS actually have to match also?
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Sep 28, 2014 11:14 PMby louiewu,I Read that too... They dance all around the question but they still don't say if the modules have to be added all at once.. Apple is really good at being vague on their answers. They would make great political people because they are so good at saying a lot of words without being specific.
thanks for the reply
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Sep 29, 2014 9:07 AMby Grant Bennet-Alder,In my opinion, the folks who write Apple technical documents are mathematical thinkers, and they write with mathematical precision. I find that if something is precluded, it WILL be mentioned. Issues you might encounter are not deliberately 'swept under the rug'.
The fact that Apple ships a configuration with one open slot and No specific language telling you you can't leave slots open says it will work. (But they do say it may not operate at top speed, which in the case of a 3.5 percent speed penalty is a non-issue for most users.)
Install two 8GB DIMMs (alone at first to be sure they are working) and then you can try adding two existing 4GB in the higher-numbered slots.
For two 16GB or 32GB DIMMs, they are Registered, and do not mix with "ordinary" unregistered DIMMs of smaller size.
