What memory to buy to upgrade 2009 iMac 27 inch

[dajl]

iMac 27 inch 2009 has 4 gig ram. Upgraded to Maverick and computer SLOW, so going to add more ram. Which brand to buy? Crucial? was going to add 2 4gig sticks to make 12 total. can i still keep my original 4 apple ram and add the new ones or must i remove the original 4 gig ram. Also, I see that there are several different options for the DDR3 from each manufacturer. How do I know which one to get? The specs seem the same, but the model number differs. i was planning on buying Crucial 8GB Kit (4GBx2) DDR3 1066 MT/s (PC3-8500) CL7 SODIMM 204-Pin Notebook Memory Modules CT2CP51264BC1067 from amazon. there is a kingston for 170ish but not sure why more expensive and it is worth the price. thanks for help!

 

[thedeske]

here's a reference if needed - you can keep the original 4

http://ramseeker.com/ddr3-1066-apple-memory-upgrades-macbook-pro-mac-mini-imac/

 

[eduardrw]

this is what I use in my late 2009 iMac I7: http://eshop.macsales.com/shop/memory/iMac/DDR3_21.5_27

If you have a I5/I7 CPU you could go all the way to 32GB otherwise 16GB is the limit.
I am using 12GB and the computer is rock solid and stable.

 

[Thermonuclear]

It's all here, the first place you should look:

http://www.apple.com/support/imac/intel/memory_storage/