iMac (21.5-inch, Late 2012)
iMac (21.5-inch, Late 2012) computers have two internal SDRAM slots inside the computer. The computer comes with at least 8 GB DDR3 SDRAM installed as two 4 GB DIMMs into two slots. The maximum amount of RAM the computer supports is 16 GB (an 8GB SO-DIMM in each slot).
You can configure your iMac (21.5-inch, Late 2012) with the amount of SDRAM you'd like when you're ordering it. Installed RAM module sizes can be 4 GB or 8 GB in each slot.
The memory DIMMs for iMac (21.5-inch, Late 2012) computers are not user-accessible. Visit an Apple Retail Store or Apple Authorized Service Provider if you need to replace your iMac (21.5-inch, Late 2012) computer's DRAM.
iMac (27-inch, Late 2012)
iMac (27-inch, Late 2012) computers have four SDRAM slots in a compartment located on the rear of the computer. The computer comes with at least 8 GB DDR3 SDRAM installed as two 4 GB DIMMs into two slots. The maximum amount of RAM you can install in your computer is 32 GB (an 8 GB SO-DIMM in each slot).
You can use any small-outline dual inline memory modules (SO-DIMMS) that meet all of these criteria:
- 

- PC3-12800 

- Unbuffered 

- Nonparity 

- 204-pin 

- 1600 MHz 

- DDR3 SDRAM 

You can use RAM module sizes of 4 GB or 8 GB in each slot.



DIMMs with any of the following features do not work in iMac (27-inch, Late 2012) computers:
- 

- Registers or buffers 

- PLLs 

- ECC 

- Parity 

- EDO RAM 

Always follow the upgrade instructions for memory installation. See iMac (27-inch, Late 2012): Installing or Replacing Memory for complete details.
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iMac (27-inch, Late 2012): Installing or replacing memory