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Upgrade the memory of your 2019 iMac up to 128GB

ECC memory errors

The Mac Pro uses Error Correcting Code (ECC) memory modules. ECC memory modules contain an extra bit for every byte (8 bits). This extra bit allows single-bit-per-byte errors to be detected and corrected. Multi-bit errors can also be detected, but cannot be corrected, and cause a kernel panic (crash). See my Jan 24, 2006 blog entry for more on ECC memory.

Memory errors can be caused by excessively high operating temperatures and/or cosmic rays (cosmic rays are considerably more of a problem at high altitudes, making one wonder why laptops don’t use ECC memory; they often are used on airplanes at 30,000'). Poor-quality memory chips are also more subject to random errors than high-quality memory.

Today, with diglloydTools run-stress-test running on 9GB of memory, I left for the office. I had intended an 8-hour test, but I inadvertently started the test at the default run time of 1 hour. So it ran for an hour, then the Mac Pro idled (without sleeping) for another 9 hours in a closed room. The ambient temperature upon my return, as measured by the Mac Pro itself and displayed by Temperature Monitor , was 84° F. Apple alludes to ambient temperatures up to 95° F for FB-DIMM modules in Technical Note TN2156, and my test was 12° F below that temperature—hardly an extreme test.

Upon my return, I checked the memory status (About This Mac => More Info => Memory). This is what you don’t want to see—ECC memory errors (but at least they were all correctable).



Rebooting did not make the errors go away; after reboot DIMM A2 still reported 88339 “ECC Correctable Errors”. However, cooling the room down by about 10° F was sufficient to make all ECC Errors vanish. The wonderful thing about ECC memory is that instead of a mysterious system crash, the system just keeps working. No data corruption, and no system crash. Good stuff.

The 2GB module in question is one of the SATech modules previously discussed. I will be asking for a replacement of that module. It’s hard to say if the non-compliant heat sinks on the 2GB modules are part of the problem, but I don’t want to use memory that has any ECC errors.

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