in which memory bays?

[zoran]

Can anyone remember in which bays of the mid 2010 27" iMac were the original 2+2 (4GB) of Ram installed?
Here is a pic of the situation now, after the installation of 2 more 8GB (16GB). In the pic u can see 20GB of total.

 

[velocityg4]

It comes with the top two slots populated. Top being the slots closest to the display.

Only the top slots allow for a single DIMM. So, if you had something like three DIMMS. You'd want them populated Bottom, Bottom, Top.

 

[zoran]

Bottom, Bottom, Top means?

 

[velocityg4]

Top is closest to the display. Bottom is closest to the back. If you just had three DIMMS. Since the Bottom can't work with a single DIMM but the Top can. You'd place two in the Bottom slots and one in the Top slot. That's how Apple's support article refers to them.