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Server and Desktop Memory

Can you mix Server and Desktop memory? If you can't, I don't understand why. Have read several posts. They don't really explain why.

Mac Pro, OS X Mountain Lion (10.8.2), Mac Pro 4.1

Posted on Feb 11, 2013 9:03 AM

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10 replies

Feb 11, 2013 9:20 AM in response to straycat23

Those are both fairly vague terms. The only thing they actually exclude is low-power SO-DIMM memory used in laptops and some iMacs and Minis.


For a Mac Pro, you need Error Correcting Code memory (which would probably be the "Server" memory in your reference). These modules are 64 data bits wide, plus an additional 8 syndrome bits. The syndrome is computed and stored on each write, and read out and checked on each read from memory.


Syndrome and data bits are evaluated in complex Hardware in the Xeon processor to check for memory errors that may have occurred, and provide enough redundant information to do on-the-fly Error Correction of single bit errors. Many other kinds of Errors can also be detected (but not corrected) and these will cause your Mac Pro to halt with a Kernel panic, Machine check, uncorrectable error.


It is folly to ignore this feature and install non-ECC memory. This will defeat the feature and leave you subject to data corruption if memory error occurs. This is a false economy. Buy the ECC memory. You paid for the Error Correction feature when you bought the Mac Pro.


I all of this is just word-salad, please post back and I will be happy to elaborate.

Feb 11, 2013 10:36 AM in response to Grant Bennet-Alder

Both are supposedly ECC registered memory. Two sticks are EBJ82HF4B1RA-AE-E. These are Elpida with heat shields. The others are Mac approved memory MT18JSF25672AZ-1G1F1. I get the blinking light on startup. Both work in the computer but not mixed. The Elpida are, I assume, to be server memory while, I guessing the MT to be desktop. No heat shield on these.

Feb 11, 2013 11:01 AM in response to straycat23

The Mac Pro has made some very important design decisions concerning airflow and fan noise.


Mac Pro modules must have Apple-Approved heat sensors on board each module. All DIMMs used in the Mac Pro MUST have heat spreaders. For Mac Pro 3,1 (2008) and previous models, these must be "3-dimensional" heat spreaders with substantial "fins" for improved cooling. For the 4,1 (2009) and later models, 3-D heatsinks are not as important, but it still MUST have a heat-speader or heat-sink of some description.


If you have been sent modules that do not conform to this description, do not debug, send them back. They are not suitable for use in a Mac Pro.


It is a common issue that different sizes from different Vendors sometimes do not mix. You need to deal with a Vendor that will work with you to get modules that will work together.

Feb 11, 2013 11:48 AM in response to Grant Bennet-Alder

So, I'm guessing from your rersponse, that the Elpida with the heat spreaders are good to use in my Mac Pro 4.1, and the Micron without the heat spreaders should not be used with my Mac Pro. I was wondering why the Micron didn't have the heat spreaders. My Mac Pro 1.1 had the dimensional type on its memory modules.


I've noticed my power consumption has decreased since I pulled the Micron and replaced them with the Elpida. Less Fan noise from the power supply. Of course, I haven't been downloading and installing apps as much. Thanks for the help.

Feb 11, 2013 12:54 PM in response to straycat23

I've noticed my power consumption has decreased since I pulled the Micron and replaced them with the Elpida. Less Fan noise from the power supply.

The reason you need to meet BOTH the heatspreaders AND the Apple-Approved temperature sensors is that Mac Fan speed is determined by measured temperatures, and Temperature sensors not approved by Apple often send wacky readings, that send the fans way up high.

Feb 11, 2013 1:43 PM in response to Grant Bennet-Alder

Grant Bennet-Alder wrote:


I've noticed my power consumption has decreased since I pulled the Micron and replaced them with the Elpida. Less Fan noise from the power supply.

The reason you need to meet BOTH the heatspreaders AND the Apple-Approved temperature sensors is that Mac Fan speed is determined by measured temperatures, and Temperature sensors not approved by Apple often send wacky readings, that send the fans way up high.

I'm not sure if the Elpida has Apple approved thermal sensors, but I can sure tell the difference in the fan noise. My computer is running very quietly now. Maybe Elpida, at least, meets the Apple specs.

Server and Desktop Memory

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