MacBook Pro: Memory Slot 0 and Slot 1

My aging MacBook Pro (13-inch, Mid-2009) has developed a new problem. The memory sometimes “disappears” and one of the two 4GB DIMMs stops working. The problem manifests itself when trying to wake my computer from sleep: it won’t wake up! The computer is still running. I can hear the fan running and feels warm to the touch, but the display stays black. A hard reboot always brings the computer back to life, although this is not an ideal solution.

A few weeks ago, when I tried to reboot the computer, I got the dreaded three beeps. I removed the bottom case, removed the memory, swapped their locations, and reinstalled it. That fixed the problem. Both memory DIMMs were registering but one of them was reporting only 7.75 GB of RAM. System Profile reports Slot 1 as empty, but I couldn’t tell which one was Slot 1. As far as I can tell, the slots are not labelled.

When you look in “About this Mac” and select the Memory tab, it shows that my MacBook Pro has two memory slots. One on the left, with memory installed, and one on the right, which is empty.

MacBook Pro Memory Banks

Which memory slot is which? On the logic board, the memory sits vertically, one on top of another, not side-by-side. After removing a few DIMMs and placing them in different memory slots, here’s what I figured out.

Bank About this Mac Physical Location
0 Left Closer to Bottom Case
1 Right Closer to Logic Board

When the computer is upside down, you can see both slots. One is at the bottom and closer to the logic board. That is Slot 1. Slot 0 is the one that’s closer to you and the bottom case.

This should help you concentrate your efforts in determining whether you have a bad DIMM, a bad memory slot, or the DIMM is just loose.

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  1. Same problem, getting more frequent. Each time slot went bad had to take back off and reseat the dimms – usually then both memory would be detected on reboot. But just recently this temporary fix no longer worked – so nothing for it but to investigate deeper and time to take logic board out.

    On closer inspection with logic board removed I could see that there was slight curvature of the bottom slot caused by heat warp. So I tried a new remedy and loosen the 4 screws this opened up a gap between the two dimms. I then cut a strip of 2mm thick stiff plastic card and inserted this in the gap between the two dimms and retightened the 4 screws. This seems to have braced the two dimms more together and straightened the curvature caused by the heat warp.

    After reinstallation of the logic board and reassembly, after insert of the dimms and reboot. both are now recognised – running on 8 GB again.

  2. I have the same problem now. I think my logic board is about to give way. Did you ever solve your memory missing issue? Power issue, too? Your other findings would be helpful. Thanks!