iMac Intel, Alu 21.5" Family
Below are listed all the ranges within the 21.5" Aluminium Intel iMac family. There is little to differentiate these ranges other than the date they were manufactured.
If you are unsure which range you have, enter your serial number in the "Identify My Mac" box to the left. Click the "?" help link if you don't know where to find your serial number.