Caution: Prior to the current iMac model it was very easy to supplement the memory on a 21.5" iMac by inserting additional memory modules. However, on the current 21.5" model (only) Apple no longer supports user memory upgrades - there are no longer externally accessible slots. The standard RAM is 8GB. If you're buying the 21.5" iMac, go for the extra bucks and get the 16GB version at time of purchase. On the other hand, the 27" iMac comes with 8GB RAM and can be user upgraded to 16GB or 32GB by adding SO-DIMM modules.