iMac not seeing all 16GB of RAM installed

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Level 1

8 points

iMac not seeing all 16GB of RAM installed

I have a 27", Late 2009 iMac. 2.8 GHz i7. I got some RAM this Christmas to upgrade from the stock 4 GB it came with.

I put 4 - 4GB sticks into it, but it only sees 8 GB of it. I have re-seated and rearranged the sticks a few times, but it still only sees half of them.

Here is what the System Information page looks like on memory:

Could there be an EFI update or something I'm missing? I'm attaching my Hardware Overview as well

iMac, OS X Yosemite (10.10.5)

Posted on Dec 28, 2015 9:41 AM

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Answer 1

poikkeus1

Level 4

2,474 points

Dec 28, 2015 10:01 AM in response to kjones3d

You've installed and reinstalled the RAM sticks, and end up with the same results every time.

By process of elimination, the RAM is faulty, or you mistakenly purchased 8GB instead of 16. (Or the vendor sent you the incorrect amount of RAM, which is a real possibility....) In any case, you'd best check your receipts, then (if necessary) call the vendor to tell them there was a mistake. Many vendors have a no questions asked return policy for a few days or weeks after purchase.

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Answer 2

Duane

Level 10

124,293 points

Dec 28, 2015 12:15 PM in response to kjones3d

So it is either the memory or the slots.

If you move the 2 RAM which are recognized into other slots, are the new slots recognized?

OR are only the 2 current slots recognized regardless of which RAM you have installed into those slots?

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Answer 3

kjones3d Author

Level 1

8 points

Dec 28, 2015 11:37 AM in response to Duane

Only those slots are recognized regardless of which sticks go in the slots. So I'm convinced it's an issue with my iMac. I'm just hoping it's not a major issue and that I can fix it at home.

the only thing I haven't done yet is to put the original RAM back in and see what it showed originally.

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Answer 4

Duane

Level 10

124,293 points

Dec 28, 2015 11:48 AM in response to kjones3d

The reasons that come to mind as to why those slots wouldn't recognize the RAM are:

The RAM is not compatible. -- By switching the RAM to other slots you have shown that this is not an issue.
The RAM is defective. -- By switching the RAM to other slots you have shown that this is not an issue.
The RAM is not installed correctly.
The slots are defective. -- This would require a motherboard replacement.

Was the original RAM in 4 slots or only 2?

If it was only 2 are those the 2 slots that are working or the 2 slots which are not working?

BTW, if you click on "Memory" in the left column of that system report, it will show you a lot more detail about each slot.

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Answer 5

kjones3d Author

Level 1

8 points

Dec 28, 2015 12:24 PM in response to Duane

OK, so I went and put the RAM back to the stock configuration and this was the result on the memory screen:

so originally it saw 2GB in the two bays, across both channels.

My next experiment was to just add 4GB sticks to fill up the rest of the bays and I got this:

So when I add the memory in, it stops reading the RAM in Bank 0

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Answer 6

Duane

Level 10

124,293 points

Dec 28, 2015 12:29 PM in response to kjones3d

Have you tried an SMC reset? Resetting the System Management Controller (SMC) on your Mac - Apple Support

Have you tried resetting the NVRAM? How to Reset NVRAM on your Mac - Apple Support

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Answer 7

kjones3d Author

Level 1

8 points

Dec 28, 2015 9:54 PM in response to Duane

I did the reset to no avail.

I played around with placement of the sticks (2 2gb and 2 4gb) in an attempt to get the most out of what I've got, but as long as the 2 and 4gb sticks are in the same channel, the 4gb sticks aren't being recognized. Interestingly enough, the 2gb sticks are recognized in both channel 0 and 1, but not the 4gb sticks in the opposite channel it just says those DIMMs are empty (but if I mix it up like I did earlier with a 4 and a 2 in each channel, it'll see 6gb).

I tried the 2 leftover 4gb sticks in my 2010 MacBook Pro and they're working just fine. Because of that, I still feel like it's a hardware or firmware issue with the iMac.

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