Full Details from Amazon.com : http://www.amazon.com/gp/product/B007HAXGLQ?tag=onigi-20
4GB kit (2GBx2) Upgrade for a Apple iMac 2.7GHz Intel Core i5 (27-inch - DDR3) Mid 2011 System
204-pin SODIMM
DDR3-1333
DDR3 PC3-10600 Unbuffered NON-ECC DDR3-1333 15V 256Meg x 64
The only brand of memory upgrade available directly from a DRAM manufacturer tested to meet the most stringent industry specifications
Install it yourself in about 15 minutes The same top-quality memory that the worlds largest computer manufacturers install in the systems they sell