Today the RAM I bought from ebay arrived. After installing it into my MBP, I discovered it did not work. Tried different arrangements with no luck, and it did not work in the iMac either. Soon after I started writing a thread about it, I discovered my mistake. On Apple's support page about MacBook Pro RAM, clicking Mid-2009 MacBook Pro scrolled me down to the beginning of the section instead of directly to the table for 2009 MBP. So I was reading the table for the 2012 Mac instead of 2009 Mac and this is why I got the wrong RAM. Luckily it had a hassle-free return policy, so I am returning it. The RAM i bought from ebay was 1600MHz RAM. My MacBook Pro takes 1066MHz RAM. Probably why it didn't work. But this confused me, because the original RAM that came with my MBP (it was bought from eBay) was 1333MHz RAM (2x4GB) and it worked. It worked, but it crashed randomly. I thought that RAM was defective. But perhaps this RAM is not defective after all... perhaps it was just causing my computer to crash randomly because it was the wrong speed. Could it be? If so then I could sell it and use the profits to pay for replacement RAM! TL;DR Could higher RAM speeds than required for a Mac cause erratic behavior? Could the 1333MHz RAM which I thought was defective be actually not?