Will going from my current 16 Gb arrangement (4x4Gb) to a 32 Gb (2x16Gb) roughly be equal memory availability on my 6 core, 3.5 Ghz Mac Pro? When the funds are available I plan to add another 16Gb module to run the total to 48Gb of memory running 3 slots? Work is 3d modeling and rendering.
Mac Pro, iOS 8.4.1, AMD FirePro D500 3072 MB graphics
Last time I checked 32GB was twice as much as 16GB.
¿so what is your question?
Misstated; can I do switch from 4x4Gb to 2x8Gb memory? Could I go to 2x16Gb...or in other words, is there some prohibition by Apple (outside the sticks have to be equal) which says I have to fill all four of the memory slots?
You can mix capacities. However, the smaller capacity sticks are not Registered and the 16 GB and larger sticks are typically Registered. You can't mix un-Registered and Registered sticks
https://support.apple.com/en-us/HT202892
http://blog.macsales.com/22745-mix-and-match-more-memory-faster-mac-pro-2
Apple ships some configurations with only three slots populated, so empty slot ARE permitted. [I believe you can run ONE 16GB stick, but no one seems to have reported testing that configuration.]
Experts, including OWC [lllaass has provided the link to their study above] have determined that sizes can be freely mixed EXCEPT: 16GB modules are Registered (contain a buffer register) and cannot be intermixed with Unregistered smaller modules. [so if you ever anticipate going to multiple 16GB modules, consider starting now.]
There are slight speed improvements when size-and-speed-matched modules are paired in adjacent slots, but real-world speed differences appear to be very small indeed. (this is probably due the the multiple levels of caches used in the Xeon Processors.)
When buying modules for Macs, always buy from a Mac-Centric vendor who assures you:
"It works in your Mac,
or your money back."
Best installation practice is to test the new modules by themselves to assure they are working, THEN add old modules to decide whether old and new can "play nice together".
Remember that Mac Pro with Xeon Processor has error-correcting memory. Problems do not fester undetected -- real issues will be immediately obvious. (such as the slots will be declared "empty" or the Mac will just sit there and blink the power light.)
From reading the link above, speed improvements are a matter of how intense the usage is for the application. In other words, if 12 Gb is enough for a low usage application, adding more memory will have little effect. The recommendation I have is 32Gb min. for the application I use mostly, Revit. I've already burned out my "work station" PC and have stressed my fill in, Macbook Pro. I'm trying not to do this again with my Mac Pro, so bumping up ram is an easy choice. My eventual goal is at least 48 Gb. If its too much out of the gate, then its cheap insurance for down the road. I not sure many benchmarks really calculate wear and tear over the life of the machine.
Thanks for your input. I will return to let you know how it works out.
Then you need to assume and plan on buying registered DIMMs, and 16GB modules (or even 32GB RDIMMs, the largest available).
Thanks, I already have: 32GB Kit (16GBx2) DDR3 PC3-14900 Registered ECC 2048Meg x 72 kit (Money back if not satisfied).
Memory allocation?
