Can I mix 2*2 memory sticks with 2*4 in a Imac 27 i5

Question

I have an iMac 27" with 2x 2GB memory sticks. Can I add 2x 4GB memory sticks?

Does it matter how they are installed in the system?

Answer 1

Apple support

Maximum memory 16 GB

Note: For the iMac (Late 2009) models, you can use 2 GB or 4 GB RAM SO-DIMMs of 1066 MHz DDR3 SDRAM in each slot. For the iMac (Mid 2010) and iMac (Mid 2011) models, use 2 GB or 4 GB RAM SO-DIMMs of 1333 MHz DDR3 SDRAM in each slot.

As for installation:

i5 and i7 Quad Core iMac computers come with both top memory slots populated. These computers will not start up if only a single DIMM is installed in any bottom slot; these computers should operate normally with a single DIMM installed in any top slot. Core Duo iMac computers should operate normally with a single DIMM installed in any slot, top or bottom. ("Top" and "bottom" slots refer to the orientation of the slots in the pictures below. "Top" refers to the slots closest to the display; "bottom" refers to the slots closest to the stand).

There is more relevant information in the top link.