2012 iMac 27" Upgraded RAM, incorrect speed.

Since apple OEM ram is 1333MHz, the ram bus will run at THAT speed. The system has a certain speed it can run at, and that is where it stays, especially when the slower ram is in the primary ram slot. Whether or not taking the OEM ram out will make it run at 1600, I cannot say as I have not actually tried doing so, but I DO know that the slower memory will slow down the ram bus to the maximum speed of the lowest chip.

The way ram works (if I understand your question) is the ram is constantly there, just incase. Instead of constantly reading and passing data through the processor (which is a very slow task,) some operations are stored on ram chips so that they can more easily be cached and replicated later. It is basically a computer's ability to multi-task several operations. Now... as far as the availability of the ram goes, Part of the ram is "wired ram" which is reserved for system operations... Anything that runs the OS and the machine itself falls in this category. Then there is "active" ram, which is ram that is currently in use by various programs. Next, there is "inactive ram" which is ram that has been used, but not yet garbage collected, and then finally, there is "free" ram, which is ram that is currently empty and can be allocated easily. As for the manufacturer anomalies, That is a fairly small window if you use good ram, so it is not usually anything to worry about.

As for the original problem, I am not sure why you would see the slower ram speed of 1333Mhz. I would say, if it isn't too annoying, and it isn't getting worse, don't worry about it. Even at 1333Mhz, you should still see a noticable improvement in speed between 8GB and 16GB.

an Apple Genius representative would likely be able to pinpoint the source of the slow-down, yes. If you bought AppleCare, that would also probably help things along as well.

What does the system info on the Mac say about your RAM?

Apple > About this Mac:

And, under more infor > Memory:

Post the results here; you may have to call Apple - you are under warranty.

I find it interesting (or, rather, disturbing) that the second screenshot says "each of which accepts a 1333 MHz, etc"

This is going to sound totally crazy, but I'd check on which iMac I received - according to the specs, the late 2012 accepts 1600 MHz.

Oh, and one more place to check:

Apple > about this mac > more info > System Report > highlight Memory in left column: same result showing 1333 MHz?

babowa wrote:

I find it interesting (or, rather, disturbing) that the second screenshot says "each of which accepts a 1333 MHz, etc"

This is going to sound totally crazy, but I'd check on which iMac I received - according to the specs, the late 2012 accepts 1600 MHz.

What does it say in "overview" wouldnt that show what model it really was?

Yes, it just seems odd: the OP's screemshot shows the 2.9 GHz i5 and that is a late 2012, but then why does it not show the correct RAM speed? It shoes the speed of the previous models (2010/2011).

I'm not at my iMac right now, so can't check, but did you install the memory so it would match horizontally? It needs to be matched that way - your Corsair screen shot shows the RAM matched vertically. You need to change that.