The memory I bought for my mac mini will not work in an iMac 24-inc.The Ram speed I bought was 1333 MHz . I did a fast check in Google for the spec of the iMac 24 early 2009 and its memory's speed is slower or 1066 MHz. Before you buy ram memory, check Apple's specs for your machine. This is what I did when I bought my memory. If you buy the wrong memory it could damage your machine so be careful.I did see inexpensive memory for your machine,but, again double check before you buy any memory.GK mentioned 1066MHz DDR3 SDRAM and this seems to be correct, again double check.
Read Entire Message: I am not sure, I was confused by this as well. I wanted to know if it worked on PC or Mac, so I called Crucial and they did a cross reference and it seems to work for both...HOWEVER, it does depend on the model numbers. You can not cross reference this yourself on their website because the stock number on Crucial and the stock number given on Amazon are different, but they are the same product (sometimes). My suggestion is to call Crucial and ask them. look for number on their site or this is number I called: 800-336-8915. Note: They are very kind and the price that is given on Amazon is the best. Good Luck!