A couple years back I had either 1 or 2 gb memory installed into my imac and after probably a yr or 2 it made my computer act horrible because it was faulty somehow. Okay fast forward, I went ahead and bought Patriot 2 gb PC2-5300 677MHz http://www.frys.com/product/5546940?site=sr:SEARCH:MAIN_RSLT_PG After installing in the in Bank 0/Bimm0 and booting it. it seem to have work fine. I go out to get something to eat and my dad turned on the computer and didn't want to boot up to desktop screen interface, it just stalls and rainbow mouse ball. it ended up freezing my computer. The reason I bought the memory was to install Lion OSX, which require 2 gb of memory. Right now it has 2gb 512mb. So I removed the 2 gb memory to Bank 1/Bimm1. Started the mac and seem to run fine then. But later in the night the mouse started to act weird like if was harder to move mouse around. the mouse has new batteries. Its seem to be running fine today. I also did pram reboot a few times. So should I return the memory? If I do that I would be only using 1gb memory. I haven't installed Lion yet until I play with the mac a bit more.