Problem with 16GB on 2010 iMac 27" i5 & i7.

New 27" iMac. Been having problems after upgrading to 16GB Mushkin 976647A. Uninstalled 8GB, and the remaining 8GB fine. Swapped those 8GB with the remaining 8GB, and that was fine too. Reinstalled 16GB, and everything was haywire again. Don't think the modules are screwed up...more like, something wrong with the iMac itself.

Either way, easiest way to repro this for me was installing Windows 7 in Parallels. Dies sometime during the "Expanding files" stage. Another way I found is to create an ISO of a large DVD, then do an MD5 checksum. The two checksums will come out differently (make a control version without the 16GB first, of course =). Maybe I should write a small program to open up the two files to see where the memory corruption is happening....

they seat correctly yes.

and all modules show up in system profiler.

I didnt try to use them one by one.

The two slots they are ok because I run it more than two months with the 2x2GB and have no problem.

I will run the test

thank you!

Same issue here with a 27'' i5 mid 2011

I got 4 x 4gb and the 2x2gb original ram, works fine with any combinaison using 8 or 12 gb ram, but it just won't start with 4x4gb plugged....

I'll see what will be less frustrating between using only 12gb ram instead of 16, or talking to someone at the apple care

I have an iMac 11,1 - Late 2009 iMac.

I have just purchased 16GB RAM from Crucial using their Memory Advisor tool - it told me I should buy PC3-8500 4GB 204-pin SODIMM CL7 DDR3 512Mx64. Right now memory is at silly cheap prices, 16GB cost me just £70.

I received the RAM the next day (amazing delivery time!), fitted all of it (taking out all of the 8x 2GB modules) and everything is working fine. I have been testing it by running VMs in VMWare Fusion - I got to seven VMs running at once before the physical RAM ran out (a couple of the VMs have more than 1GB allocated). I ran it like this for several hours without any problems, the iMac was still zippy and responsive and all of the VMs worked fine too (bottleneck was the hard drive as the VMs did their own updates etc).

This PC3-8500 is what Apple recommend for my Mac, so I would ignore what the latest RAM is and just buy what Apple recommend, or what the Crucial Memory Advisor tool tells you for your precise model. If it turns out to be slightly more expensive then that is the price you pay for reliability. I have seen newer RAM fail in PC hardware designed for older RAM, this is not just an Apple thing.

When looking into a 16GB RAM upgrade I came across these threads, and as there was no concrete answer as to whether or not the full 16GB has been shown to work in my iMac model (at least, I couldn't find one), I decided to add my findings. As my iMac is more than six months old this thread is still relevant. If one person finds only one of these threads looking for an answer and finds my post useful, it will surely have been worth my effort.

This has everything to do with the RAM specs - get the incorrect RAM and you run the risk of it not working, as some posts in this and other threads prove (those that said they bought 1333MHz RAM for a Mac that originally had 1067MHz). People seem to act like OWC are the only people able to supply RAM for Macs, I have always found that Crucial RAM works perfectly and they have US and UK sites and distribution.

I don't recall anyone saying that they fitted the full 16GB in PC3-8500 SODIMMs and had problems.