I am looking to upgrade the RAM on my Early 2009 iMac from 4GB to 8GB. According to the memory specifications it accepts PC3-8500 204-pin SO-DIMMs. However, will the iMac accept faster RAM (e.g. PC3-10600)? Supposing it does, is there any benefit to doing so?

For reference, here are the two types of RAM I'm considering:

5 Answers 5


There's no benefit in going with faster RAM because the speed is limited by what your motherboard supports (the early 2009 iMac has a 1066 Mhz frontside bus.) In theory the faster RAM should be able to work at the lower speeds and should be safe to install, however macs do tend to be fussy when it comes to RAM so I would recommend sticking to the RAM recommended in the system specs.


More often than not your mac will accept higher speed RAM. However it can cause problems; one example from the Apple Support Forums. You can find similar stories all over Apple forums. This is why I advocate sticking as closely to the specs as possible.

As to the advantage of possibly installing the RAM in a future computer, in 2 years you'll probably be able to get twice the RAM for the price (and be wanting to install twice the amount too.)

Lastly, if you compare the 2 chips you linked you'll notice that the 1333 memory has a CAS latency of 9, while the 1066 has a lower (better) latency of 7. So you're trading an imaginary upside for a real downside.

  • Aren't RAM chips able to detect which frequency they're running at and apply lower latencies where possible? Certainly HWiNFO implies this - as it shows a matrix of timings for each module, with frequency down the left and latencies along each row, which in my case indicates that lower latencies would be achieved when downclocking. e.g. I have one module that lists CL11 at 1600 MHz but apparently CL9 at 1333. Commented Oct 7, 2015 at 20:26

The Memory you have noted PC3-10600 is backwards compatible with PC3-8500 as noted here by Crucial "Memory speeds and compatibility" article.

Memory is designed to be backward-compatible, so generally speaking, you can safely add faster memory to a computer that was designed to run slower memory. However, your system will operate at the speed of the slowest memory module.

The only benefit is that for newer computers that you may purchase that can accept PC3-10600, you will already have the faster memory to put in it and you will not have to re buy your memory upgrade. This might be a really good option for you if you frequently buy new computers, eg. every year or two. This could pay off best when buying the largest capacity sticks that you can put into your machine and then carry your memory upgrade with you as you upgrade to newer computer/s. However with buying the largest modules that you can buy /afford you will be paying a premium price, so it is kind of a gamble that may or may not pay off depending on the prices of memory in the future. Just factor in how much your memory upgrade will cost, and if going to PC3-10600 will be cost effective for your needs or not.


I am currently using Kingston (2 x 4GB) 204-Pin DDR3 SO-DIMM DDR3 1333 (PC3 10600) in my early 2009 24' iMac. Everything is working properly.


I own an early 2009 24" iMac as well as two Mac minis and since memory is fairly cheap I was going to up one of the minis (model 5,2) to max ram and bought 8GB (two sticks) from Crucial. While the ram was in transit I read on another site that unofficially the 5,2 models could handle and identify 16GB ram.

So when the ram arrived I installed it into the 2009 iMac even though it was 1333mhz instead of 1066mhz raising it up from 4GB to 8GB the iMac booted and identified the ram correctly and has since been running fine. It has also been upgraded to OSX 10.8.2 from 10.6.8 all without any issues.

Since then I have also installed 16GB into the mini even though Apple lists it as maxin out at 8GB and it likewise has run without any hiccups as well. For the record I got my upgrade information from this site which even though they are vendors seem to be a good source of information on how to upgrade Macs more economically that the Apple store.

  • Did it actually boost the performance of your iMac?
    – To1ne
    Commented Aug 26, 2013 at 20:34

I installed 2x 2GB DDR3 1333 PC3-10600 into a late 2009 mac mini. Running 10.10.2, which struggles on the default 2GB.

It started up fine, and apps were so snappy, but then the crashes started. The machine is completely unstable, with kernel panic errors every 30 odd seconds forcing a restart.

Sadly the original 2GB RAM has gone back in.

I'd recommend sticking to PC3-8500 for this spec mac.

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