How do you upgrade the RAM in the "Late 2009," "Mid-2010," "Mid-2011" and "Late 2011" (21.5-Inch and 27-Inch) Aluminum iMac models? What type of RAM do they use? How much RAM do they actually support?

Please note that this Q&A explains how to upgrade the RAM in the 21.5-Inch and 27-Inch Aluminum iMac models that have all aluminum cases and a flat, thick edge around the display. Apple refers to these systems as the "Late 2009," "Mid-2010, "Mid-2011" and "Late 2011" models. They can be identified by model numbers A1311 and A1312.

EveryMac.com also provides RAM upgrade instructions for the earlier 20-Inch and 24-Inch Aluminum iMac models that have black plastic backs (model numbers A1224 and A1225) as well as the "Late 2012" (and subsequent) 21.5-Inch and 27-Inch Aluminum iMac models that have all aluminum cases with edges that taper sharply around the display (model numbers A1418 and A1419).

The memory upgrade procedure in these 21.5-Inch and 27-Inch iMac models is easy, but different lines use different memory types and there are differences between official and unofficial RAM capacity as well. Precise identification can require a bit of work, too.

Photo Credit: Apple, Inc (21.5-Inch & 27-Inch Aluminum iMac Models)

Identification Help

If you're not sure which Aluminum iMac you have, these 21.5-Inch and 27-Inch models can be most simply identified externally via EMC Number -- located inconveniently under the "foot" supporting the computer -- and in software by Model Identifier for the purpose of upgrading the RAM. These models can be uniquely identified when combined with a secondary identifier like display size, processor speed and/or processor type.

To locate the model identifier in software, select "About This Mac" under the Apple Menu on your computer and click the "More Info..." button. If the iMac is running OS X 10.7 "Lion" or later, you will need to click the "System Report" button after clicking "More Info..." as well. As always, EveryMac.com has carefully hand documented each EMC number and model identifier for your convenience.

These identifiers for each of these 21.5-Inch and 27-Inch iMac models follow:

iMac	Subfamily	EMC	Model ID
"Core 2 Duo" 3.06 21.5"	Late 2009	2308	iMac10,1
"Core 2 Duo" 3.33 21.5"	Late 2009	2308	iMac10,1
"Core 2 Duo" 3.06 27"	Late 2009	2309	iMac10,1
"Core 2 Duo" 3.33 27"	Late 2009	2309	iMac10,1
"Core i5" 2.66 27"	Late 2009	2374	iMac11,1
"Core i7" 2.8 27"	Late 2009	2374	iMac11,1
"Core i3" 3.06 21.5"	Mid-2010	2389	iMac11,2
"Core i3" 3.2 21.5"	Mid-2010	2389	iMac11,2
"Core i5" 3.6 21.5"	Mid-2010	2389	iMac11,2
"Core i3" 3.2 27"	Mid-2010	2390	iMac11,3
"Core i5" 2.8 27"	Mid-2010	2390	iMac11,3
"Core i5" 3.6 27"	Mid-2010	2390	iMac11,3
"Core i7" 2.93 27"	Mid-2010	2390	iMac11,3
"Core i5" 2.5 21.5"	Mid-2011	2428	iMac12,1
"Core i5" 2.7 21.5"	Mid-2011	2428	iMac12,1
"Core i7" 2.8 21.5"	Mid-2011	2428	iMac12,1
"Core i5" 2.7 27"	Mid-2011	2429	iMac12,2
"Core i5" 3.1 27"	Mid-2011	2429	iMac12,2
"Core i7" 3.4 27"	Mid-2011	2429	iMac12,2
"Core i3" 3.1 21.5" (Edu)	Late 2011	2496	iMac12,1

If your 21.5-Inch or 27-Inch iMac is not listed above, you have a later"Tapered Edge" iMac model.

EveryMac.com's Ultimate Mac Lookup feature also can uniquely identify these models by their Serial Number, which is listed on the underside of the foot along with the EMC number and within the operating system alongside the model identifier. More details about specific identifiers are provided in EveryMac.com's extensive Mac Identification section.

RAM Types & Actual Maximum RAM Capacities

All of these 21.5-Inch and 27-Inch Aluminum iMac models have RAM slots that are readily accessible via a small "door" on the underside of the display. However, the type of 204-pin SO-DIMM and the actual maximum capacity varies.

Specifically, the "Late 2009" iMac (iMac10,1 and iMac11,1) models use 1066 MHz PC3-8500 DDR3 SO-DIMMs whereas the "Mid-2010," "Mid-2011" and "Late 2011" iMac models all use 1333 MHz PC3-10600 DDR3 SO-DIMMs.

Officially, the education-only "Late 2011" iMac model will support a maximum of 8 GB of RAM, but it actually is capable of supporting 16 GB. The rest of these models all officially support a maximum of 16 GB of RAM -- and this also is the actual maximum RAM for some models -- but other models actually are capable of supporting 32 GB under certain conditions.

As it can be confusing, these details definitely are easiest to visualize as a chart:

iMac	EMC	Model ID	SO-DIMM	Max
"Core 2 Duo" 3.06 21.5"	2308	iMac10,1	1066 PC3-8500	16 GB
"Core 2 Duo" 3.33 21.5"	2308	iMac10,1	1066 PC3-8500	16 GB
"Core 2 Duo" 3.06 27"	2309	iMac10,1	1066 PC3-8500	16 GB
"Core 2 Duo" 3.33 27"	2309	iMac10,1	1066 PC3-8500	16 GB
"Core i5" 2.66 27"	2309	iMac11,1	1066 PC3-8500	32 GB*
"Core i7" 2.8 27"	2309	iMac11,1	1066 PC3-8500	32 GB*
"Core i3" 3.06 21.5"	2389	iMac11,2	1333 PC3-10600	16 GB†
"Core i3" 3.2 21.5"	2389	iMac11,2	1333 PC3-10600	16 GB†
"Core i5" 3.6 21.5"	2389	iMac11,2	1333 PC3-10600	16 GB†
"Core i3" 3.2 27"	2390	iMac11,3	1333 PC3-10600	16 GB†
"Core i5" 2.8 27"	2390	iMac11,3	1333 PC3-10600	32 GB
"Core i5" 3.6 27"	2390	iMac11,3	1333 PC3-10600	32 GB
"Core i7" 2.93 27"	2390	iMac11,3	1333 PC3-10600	32 GB
"Core i5" 2.5 21.5"	2428	iMac12,1	1333 PC3-10600	32 GB
"Core i5" 2.7 21.5"	2428	iMac12,1	1333 PC3-10600	32 GB
"Core i7" 2.8 21.5"	2428	iMac12,1	1333 PC3-10600	32 GB
"Core i5" 2.7 27"	2429	iMac12,2	1333 PC3-10600	32 GB
"Core i5" 3.1 27"	2429	iMac12,2	1333 PC3-10600	32 GB
"Core i7" 3.4 27"	2429	iMac12,2	1333 PC3-10600	32 GB
"Core i3" 3.1 21.5" (Edu)	2496	iMac12,1	1333 PC3-10600	16 GB

* As first reported by adventurous EveryMac.com readers, and carefully confirmed by site sponsor Other World Computing, these models can support up to 32 GB of RAM if they are running Mac OS X 10.6.3 "Snow Leopard" or higher in 64-bit mode and have been updated to use the latest EFI version. They are limited to 16 GB of RAM in 32-bit mode.

† Specifically note that the 21.5" models from the Mid-2010 line (iMac11,2) and the entry-level 27-Inch model -- the iMac "Core i3" 3.2 27-Inch (Mid-2010) -- only support 16 GB of RAM whereas all models from the Mid-2011 line -- 21.5" and 27" -- actually support 32 GB of RAM. If you have a 21.5" model (or the entry-level 27-Inch "Core i3" powered Mid-2010 iMac), 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.

RAM Upgrade Instructions

Upgrading the RAM in all of these 21.5-Inch and 27-Inch iMac models is similar and easy.

The process basically consists of (1) place a soft towel (or anti-static mat) on a table or other flat surface, (2) place the iMac "face down" on its display on top of the towel or anti-static mat, (3) unscrew the access panel on the bottom of the display edge, and (4) change out the SO-DIMMs.

Apple kindly provide silkscreened pictures that cover the RAM upgrade steps on the bottom of the iMac "foot" itself and these images should be reviewed before proceeding with the RAM upgrade.

However, even better, Other World Computing provides helpful step-by-step videos of the precise procedure for each model:

21.5-Inch & 27-Inch "Late 2009" iMac RAM Upgrade Video

21.5-Inch & 27-Inch "Mid-2010" iMac RAM Upgrade Video

21.5-Inch & 27-Inch "Mid-2011/Late 2011" iMac RAM Upgrade Video

From watching the video, it should be clear that upgrading the RAM in these models is simple. However, if you do not feel comfortable -- or have the time -- to perform the upgrade yourself, hiring a professional always is a good option.

iMac RAM Purchase Options

Just because RAM meets the minimum listed criteria does not mean that it will necessarily function as intended in a particular Mac. Be sure to buy from a quality vendor that has tested their RAM with your Mac to ensure full compatibility.

In the US (and many other countries), site sponsor Other World Computing sells memory for all iMac models for do-it-yourself upgrades.

In the UK and Ireland, site sponsor Flexx sells Aluminum iMac compatible memory with free shipping. The company provides flat rate shipping to France, Germany, and Switzerland and inexpensive shipping for all of Europe, too.

In Germany, site sponsor CompuRAM sells quality memory for all iMac models with affordable delivery country-wide and in person pick up and professional installation service available in Munich.

Also see: How do you upgrade the hard drive in the "Late 2009," "Mid-2010," "Mid-2011" and "Late 2011" (21.5-Inch and 27-Inch) Aluminum iMac models? What type of storage do they support? Is it even possible to upgrade these models?