I have this computer which originally came with 4GB (2 x 2GB sticks) Ram. We upgraded to a newer model and I was getting ready to sell this one and decided it would be a better sale with more RAM. I ordered 16 GB (4 x 4GB sticks) from OWC. They just arrived today and I popped them in. System booted up fine and reported all 16 GB no problem but after about a minute there was an error tone and the system rebooted. I got on the phone with OWC support and we tried a lot of things. 2 sticks only. Then the other 2. No issues so no problem with the sticks. Tried 3 sticks and again no problem. But as soon as you have 4 in there, problems! I'm not using the machine myself right now so no problem being patient. The support guy asked if I minded running it on 3 sticks over night to see if a problem came up or not and also directed me to a memory checking utility which is running on the 3 currently installed sticks. Anyway while all this is going on I'm searching and found a thread on Apple support Community where someone had the same problem with a 2010 27" and same 4 x 4GB memory from OWC. They replaced his sticks 3 times and the problem persisted. He finally solved his issue by installing 2 x 8 GB sticks from another supplier. OWC does not list their 2 x 8 GB ram as compatible with the 2010 27". Is this a known issue? Why would 4 perfectly good memory sticks cause an iMac to crash?