Up Close with the New 27-inch iMac's User Serviceable Memory Panel

Both of the 21.5 and 27-inch iMacs use SO-DIMMs, however the 27-inch model does allow for end user upgrades. Remove the power cable and there's a button that will pop out a little panel giving you access to the system's SO-DIMM slots. The 21.5-inch model needs to be taken apart to gain access to the memory slots unfortunately.