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I've got an early 2011 13" i7 MBP, OS X 10.10.3 (the public beta version before the one released last night) with 10 GB of RAM – one of the original 2 GB modules in the bottom slot and an 8 GB module that's now a few months old in the top slot. Yesterday morning, I opened my computer to reveal a black screen after it had just been working a few minutes ago. I tried to turn it off and back on, and ended up getting the three-beep pattern that indicates bad RAM. I opened up my computer's back, and here's what I tried (and what happened when I attempted to power on after trying it):

  1. Pulling out and reinserting the RAM - no change.

  2. Pulling out the 8 GB and trying to boot with just the 2 GB - no change

  3. Pulling out the 2 GB and using just the 8 GB in the top RAM slot - no change

  4. Putting the 8 GB in the bottom slot - it booted fine!

  5. Adding in the 2 GB in the top slot - no problem!

"No trouble found." -Apple Hardware Test (both basic and extended) last night

So, here's my question: How'd my RAM spontaneously go bad enough to cause the beeps of death, and how'd the solution end up lying in switching which module goes in which slot?

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    I'll throw in a recommendation for Memtest OS X. I haven't had to use it recently, but in the past I've had it spot flaky RAM that had passed all of the other test tools I tried (including Apple Hardware Test). – Gordon Davisson Mar 31 '15 at 16:44
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I couldn't possibly venture a guess as to "why" except to chalk it up to Murphy...

However Mac O/S is very picky when it comes to RAM. It is my guess that Apple updated some of the code in the O/S that checks for issues with RAM and it noticed a problem.

That it now works with the RAM effectively swapped is even more puzzling. It is possible that there is an issue with something in the RAM slot itself, either physical or "electro-mechanical."

If the RAM is within warranty I would contact the folks you bought it from and swap it out on the chance that there is a strange issue with the RAM itself.

Sorry, no real definitive answer. It could be just a random occurrence and if you swap the RAM again it could work fine. Or the Earth could veer out of it's orbit and go crashing into the sun... Sometimes troubleshooting hardware and software issues leads you down a road that makes no sense, but if your "fix" works then leave it be and hope for the best.

Any any time I hope for the best, I make sure I have a recent backup...

  • I guess OS X's picky code would explain it, especially considering I'm on beta software and the Apple Hardware Test that hasn't changed since early 2011 found nothing wrong. Thank you! – user24601 Mar 31 '15 at 15:50
  • I had a 2007 MacBook that, after 5 years would just shut down with no warning. Strangely enough the only thing that fixed it was to install Windows 7. It was perfectly stable under Windows, under Mac OS, not so much. Very strange... – Steve Chambers Jul 3 '15 at 20:18

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