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I had problems (strange patterns on the display and reboots) with my Late 2011 Macbook Pro, so I ran Apple Hardware Test on my computer, and it found memory errors. The thing is that every time I run the AHT, the error is slightly different. The first time, I got:

4MEM/62/40000000: 0x83a65498

The second time:

4MEM/62/40000000: 0x836dc298

I then swapped my two memory sticks and got this error:

4MEM/62/40000000: 0x842e1198

I am assuming that the hex number is the address where the test fails…

It always takes about 13.5 minutes of tests for the error to appear. Rambler also found an error during one pass of tests out of two:

FAILURE! Data mismatch at local BUFA address 0x000000012479b930, BUFB address 0x00000001c96da130 BUFA Data: 0xffffffff80000000, BUFB Data: 0xffffdfff80000000

Memtest86 did not find any problem after 4 passes.

Because the error is different each time, I was wondering if I should suspect something else than a memory stick being bad, something like the memory controller.

UPDATE:

However, I am not getting any error message, if I run the AHT while there is only one memory stick in my MBP.

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I haven't been able to find documentation of what these fields mean.

However, given that memory failures that I've seen and those posted by others all appear to be around "address" 0x842XXXXX, I suspect that this is not in fact the address. It may be the pattern being written to some address when the failure occurred.

The field where you have a value of 62 seems to be the only one that varies significantly. It may be that this value represents the address to some very course degree (eg. maybe 1-64 could represent one DIMM and 65-128 the other; or maybe odd numbers vs even numbers).

It would be nice if Apple would document these very basic and useful error code formats.

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