How do you upgrade the RAM in the "Aluminum" iMac models? How much RAM of what type do these systems actually support?

Upgrading the memory in all Aluminum iMac models is quick and easy, but different lines use different types of memory and there are differences between official and unofficial capacity as well.

Identification Help

If you're not sure which Aluminum iMac you have, these models can be most readily identified externally via EMC number (located inconveniently under the "foot" supporting the computer) and in software by model identifier (close enough to an exact match to determine RAM type by itself and the actual maximum RAM when combined with a secondary identifier like processor speed and/or processor type.

These models also can be identified by the last three or four characters of the serial number -- the last three characters if it has an eleven character serial number and the last four characters if it has a twelve character serial number -- using EveryMac.com's Ultimate Mac Lookup feature.

Supported RAM Types

The "original/Mid-2007" Aluminum models -- the iMac "Core 2 Duo" 2.0 20-Inch (Al), "Core 2 Duo" 2.4 20-Inch (Al), "Core 2 Duo" 2.4 24-Inch (Al), and "Core 2 Extreme" 2.8 24-Inch (Al) -- use 667 MHz PC2-5300 DDR2 SO-DIMMs, which Apple further specifies must meet all of the following criteria:

• PC2-5300
• Unbuffered
• Nonparity
• 200-pin
• 667 MHz DDR2 SDRAM

The "Early 2008" Aluminum models -- the iMac "Core 2 Duo" 2.4 20-Inch (08), 2.66 20-Inch (08), 2.8 24-Inch (08), and 3.06 24-Inch (08) -- use 800 MHz PC2-6400 DDR2 SO-DIMMs, or specifically:

• PC2-6400
• Unbuffered
• Nonparity
• 200-pin
• 800 MHz DDR2 SDRAM

The "Early 2009" Aluminum models -- the iMac "Core 2 Duo" 2.66 20-Inch (Early 2009), 2.66 24-Inch (Early 2009), 2.93 24-Inch (Early 2009), and 3.06 24-Inch (Early 2009) -- and the "Late 2009" Aluminum models -- the iMac "Core 2 Duo" 3.06 21.5-Inch (Late 2009), "Core 2 Duo" 3.06 27-Inch (Late 2009), and "Core i5" 2.66 27-Inch (Late 2009) -- use 1066 MHz PC3-8500 DDR3 SO-DIMMs:

• PC3-8500
• Unbuffered
• Nonparity
• 204-pin
• 1066 MHz DDR3 SDRAM

However, the "Early 2009" models have two RAM slots whereas the "Late 2009" models have four RAM slots.

The "Mid-2010" Aluminum models -- the iMac "Core i3" 3.06 21.5-Inch, "Core i3" 3.2 21.5-Inch, "Core i3" 3.2 27-Inch, and "Core i5" 2.8 27-Inch, the "Mid-2011" Aluminum models -- the iMac "Core i5" 2.5 21.5", "Core i5" 2.7 21.5", iMac "Core i5" 2.7 27", and "Core i5" 3.1 27" -- as well as the education-only "Late 2011" model -- the iMac "Core i3" 3.1 21.5" (Late 2011) -- all use 1333 MHz PC3-10600 DDR3 SO-DIMMs:

• PC3-10600
• Unbuffered
• Nonparity
• 204-pin
• 1333 MHz DDR3 SDRAM

Actual Maximum RAM

The actual maximum RAM for each Aluminum iMac model is listed on its specs page -- along with the official maximum RAM and number of RAM slots -- as well as on EveryMac.com's Actual Maximum RAM page, but this info also is provided below for your convenience:

iMac Model	Slots	Official Max RAM	Actual Max RAM
Original/Mid-2007	2	4 GB	6 GB
Early 2008	2	4 GB	6 GB
Early 2009	2	8 GB	8 GB
Mid-2009 (Edu)	2	8 GB*	8 GB*
Late 2009	4	16 GB	16 GB
Mid-2010 (21.5")	4	16 GB	16 GB**
Mid-2010 (27")	4	16 GB	32 GB
Mid-2011 (21.5")	4	16 GB	32 GB**
Mid-2011 (27")	4	16 GB	32 GB
Late 2011 (Edu)	4	8 GB	8 GB†

*Apple originally supported 4 GB of RAM in the education-only iMac "Core 2 Duo" 2.0 20-Inch (Mid-2009) model, and it was believed to have an artificial EFI limitation that prevented 8 GB of RAM from being recognized. However, Apple later began to support 8 GB of RAM.

** Specifically note that the 21.5" models from the Mid-2010 line only support 16 GB of RAM whereas all models from the Mid-2011 line -- 21.5" and 27" -- support 32 GB of RAM. If you have a 21.5" model, please be very certain to identify it precisely to avoid potential disappointment when upgrading the RAM. The 21.5" Mid-2010 models use the 2389 EMC number whereas the 21.5" Mid-2011 models use 2428.

† The education-only "Late 2011" model officially supports 8 GB of RAM and is believed to have its maximum RAM capped at 8 GB in EFI as a point of differentiation between it and the more expensive models.

RAM Upgrade Instructions

The Apple Support Site provides a helpful document that covers "Installing or Replacing Memory" in the "two side-by-side Synchronous Dynamic Random-Access Memory (SDRAM) slots in the bottom" of the pre-"Late 2009" Aluminum iMac models and another document that cover the four slots in the subsequent Aluminum iMac models.

The upgrade procedure effectively is the same in all models except for the number of memory slots. The Apple documents provide instructions complete with drawings for upgrading the RAM in these iMac models and these should be reviewed prior to upgrading the memory.

However, perhaps even better, for the 21.5-Inch and 27-Inch "Late 2009," "Mid-2010," "Mid-2011" and "Late 2011" models in particular, site sponsor Other World Computing provides a helpful step-by-step video of the quick procedure:

Please note that just because RAM meets the minimum listed criteria does not mean that it will necessarily function as intended in a particular Mac. When buying memory, be sure to buy from a quality vendor that has tested their RAM with your Mac to ensure compatibility.

Site sponsor Other World Computing sells memory guaranteed to be compatible with all of the Intel-based iMac models.

Also see: How do you upgrade the RAM in the White iMac "Core Duo" and "Core 2 Duo" models? How much RAM of what type do these systems support?