Specifications

If you have two DIMMs, insert into slots 2 and 4 (as shown below). The slot closest to rear housing vents is Slot 1.
2. Use the DIMM insertion instructions on the inside of DIMM door as a guide.
3. Press memory firmly into slot until you feel a click.
4. Push the levers back into the rear housing until they click into the memory compartment.
5. Reinstall RAM access door.
iMac (27-inch, Late 2012) Memory Specs
Default configuration: Two (2) x 4GB modules (8GB total memory)
Memory type: 1600MHz DDR3
Four (4) user-accessible SO-DIMM slots
Configurable to 16GB or 32GB
More information can be found in Apple Support article HT5523.
Service Considerations 21.5"