2010 Mac Pro with 64GB: Normal for memory to run hot?

Question

Level 1

21 points

2010 Mac Pro with 64GB: Normal for memory to run hot?

I just upgraded my Mac Pro 5,1 (dual Xeon x5670s) to 8 x 8GB Micron 2RX4 registered DIMMs. System works fine (although I haven't stress tested it). But the memory is hot when I touch it (I can hold my hand on it for about 10 seconds before it gets too hot). Is this expected? I'm assuming the DIMMs can handle it, since they have heat spreaders; just wondering if it's something I should be concerned about.

Thanks!

Mac Pro, OS X El Capitan (10.11.4)

Posted on May 4, 2016 1:59 PM

Reply

Answer 1

macjack

Level 10

111,168 points

May 4, 2016 2:00 PM in response to swechsler

Please download and run EtreCheck, created by one of own helpers here in ASC. It is a diagnostic tool that's very useful to us in finding problems. Also it will give us further specs on your Mac. After it runs post the log file here. It will contain no personal information

Reply

Answer 2

May 4, 2016 2:37 PM in response to swechsler

These are server-grade DIMMs with extra error-correction bits added. They run hot, and die young. The fans are controlled by the SMC micro controller software, by measuring the temperatures and adjusting fan speeds in a feedback loop.

The Mac Pro silver tower has its fans set to a compromise setting that carries away most of the heat without also blowing the papers off your desk. You CAN set a new Base speed (from which the software will continue to run in a feedback loop as usual) if you wish, with programs like SMC fan Control. (but of course you cannot set the fan speeds lower.)

Reply

Answer 3

swechsler Author

Level 1

21 points

May 4, 2016 3:44 PM in response to Grant Bennet-Alder

Thanks, useful info. I knew they were server DIMMs when I purchased them, but I still don't know the difference between those and ECC DIMMs that are sold specifically for the Mac or other workstations (I also own a Dell workstation of similar vintage to the Mac that uses the same memory). Can you enlighten me further? Is it the fact that it's registered (almost all ECC DIMMs that I could find on the used market are registered)?

Reply

Answer 4

May 4, 2016 7:34 PM in response to swechsler

Registered DIMMs are DIMMs built with "too many" parallel data chips on each DIMM, because the available chips are not yet dense enough. They are used only for larger sized DIMMs. With "too many" parts, you can no longer wire-OR the outputs together and expect it all to work, the Bus Loading from so many parts gets too high and it all goes wonky.

The solution is to add a Register -- a part that buffers and re-drives the output data from the chips onto the memory bus. But registers are so strong they overwhelm any unregistered DIMMs that are built to just wire the the chip outputs onto the memory Bus. So registered DIMMs can not be mixed with (smaller sized) un-registered DIMMs.

Reply