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?

Please note that this Q&A covers Aluminum iMac models with flat edges and 21.5-Inch and 27-Inch displays. EveryMac.com also explains how to upgrade the hard drive in earlier 20-Inch and 24-Inch Aluminum iMac models as well as in later "Tapered Edge" 21.5-Inch and 27-Inch Aluminum iMac models.

Apple considers the memory in the "Late 2009," "Mid-2010" and "Mid-2011" Aluminum iMac models -- all Aluminum iMacs with 21.5-Inch and 27-Inch displays and flat sides -- to be a "customer installable part" but the hard drive is not intended to be upgraded by end users.

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

Upgrading the memory is extremely easy -- there is a small removable "door" on the bottom of each system for this purpose -- but upgrading the hard drive requires one to gingerly remove the display and effectively disassemble the entire computer.

Identification Help

If you're not sure which 21.5-Inch or 27-Inch Aluminum iMac you have, these models can be most readily identified externally via EMC number (located inconveniently under the "foot" supporting the computer). More conveniently, they can be identified in software by model identifier.

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.

The 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.

Supported Hard Drive & SSD Types

All "Late 2009" iMac models and all "Mid-2010" models have a 3 Gb/s SATA 2.0 connector for a 3.5" hard drive. The 27-Inch "Mid-2010" models -- the iMac "Core i3" 3.2 27" and "Core i5" 2.8 27" -- also have an extra 3 Gb/s SATA 2.0 connector and power for the optional 2.5" SSD (in addition to 3 Gb/s Serial ATA 2.0 connectors for the hard drive and optical drive).

The "Mid-2011" iMac models all support a single 3.5" hard drive and a second 2.5" SSD. As shipped, both the hard drive bay and SSD bay provided support for the 3 Gb/s Serial ATA 2.0 standard. However, as first discovered by site sponsor Other World Computing, the iMac EFI Update 1.6, released two days later, quietly provided faster 6 Gb/s Serial ATA 3.0 support for both of these connectors (but not the optical drive connector).

The education-only iMac "Core i3" 3.1 21.5-Inch (Late 2011) supports a single 3.5" hard drive using the 6 Gb/s Serial ATA 3.0 standard. It does not support a 2.5" SSD simultaneously with an internal hard drive.

These differences are perhaps best visualized with a chart:

iMac Series	Primary Storage	Secondary Storage
Late 2009 21.5"	3.5" 3 Gb/s SATA 2.0	None
Late 2009 27"	3.5" 3 Gb/s SATA 2.0	None
Mid-2010 21.5"	3.5" 3 Gb/s SATA 2.0	None
Mid-2010 27"	3.5" 3 Gb/s SATA 2.0	2.5" 3 Gb/s SATA 2.0
Mid-2011 21.5"	3.5" 6 Gb/s SATA 3.0	2.5" 6 Gb/s SATA 3.0
Mid-2011 27"	3.5" 6 Gb/s SATA 3.0	2.5" 6 Gb/s SATA 3.0
Late 2011 21.5"	3.5" 6 Gb/s SATA 3.0	None

The maximum drive height of the 3.5" storage drive in these models is 26.10 mm and the maximum height of the 2.5" storage drive in these models is 7 mm.

For storage compatibility details for each Mac, including all iMac models, refer to EveryMac.com's Mac Storage Upgrade Compatibility Guide.

Overcoming Hard Drive Upgrade Obstacles

Unfortunately, taking the computer apart -- which is challenging enough -- is not the only obstacle to upgrading the hard drive in these Macs.

OWC also discovered that the "Late 2009" -- and subsequently introduced "Mid-2010" -- models use a "connector that seems to use the drive's internal sensors" rather than an external sensor like earlier 20-Inch and 24-Inch Aluminum iMac models.

Originally, this meant that the most straightforward way to upgrade the hard drive was to "replace the drive with another model from the same manufacturer that [OWC or another third-party has] confirmed works properly with this thermal sensor cable". OWC provides a list of compatible drives. Readers also shared reports that taping an external temperature sensor to a hard drive or SSD that does not have an internal sensor will work in these models, but this method is risky.

Thankfully, though, OWC subsequently developed a custom digital monitor that "talks Apple SMC" and "maintains proper temperature reporting and Apple Diagnostic compatibility" for these models and sells it as part of convenient SSD Upgrade DIY Kits. Although it still is fine to replace the hard drive with another model from the same manufacturer, this OWC solution provides many more options.

As again found by OWC, if an SSD is not installed at the time of purchase in the 27-Inch "Mid-2010" models -- the iMac "Core i3" 3.2 27" and "Core i5" 2.8 27" -- the connector cables and mounting bracket are not present. It still is possible to install a 2.5" SSD in addition to the hard drive if an SSD is not installed initially, but one will need the proper connecting cable. It also is worth noting that if a 27-Inch "Mid-2010" iMac is configured with an SSD, but without a hard drive, the hard drive temperature sensor is not present either. OWC now provides the proper cables and sensors.

For the "Mid-2011" models, OWC once more touched off a firestorm across the blogosphere by reporting that Apple had gone even further in the company's effort to restrict hard drive upgrade options:

For the main 3.5" SATA hard drive bay in the new 2011 machines, Apple has altered the SATA power connector itself from a standard 4-wire power configuration to a 7-wire configuration. Hard drive temperature control is regulated by a combination of this cable and Apple proprietary firmware on the hard drive itself. From our testing, we've found that removing this drive from the system, or even from that bay itself, causes the machines hard drive fans to spin at maximum speed and replacing the drive with any non-Apple original drive will result in the iMac failing the Apple Hardware Test (AHT). . .

We've installed our Mercury Pro 6G SSD in that bay, it too results in ludicrous speed engaged fans and an AHT failure. In short, the Apple-branded main hard drive cannot be moved, removed or replaced.

Needless to say, the obstacles to upgrade the hard drive in these models was quite disappointing. Thankfully, OWC's SSD Upgrade DIY Kits now overcome all of these obstacles for each line and taking the computer apart and putting it back together again is the remaining challenge.

Hard Drive & SSD Installation Instructions

This is a difficult upgrade. It is recommended that a professional upgrade the hard drive or install an SSD in these models.

However, for highly skilled users with previous experience upgrading computers, OWC provides detailed step-by-step instructional videos for each model:

21.5-Inch Late 2009 iMac Storage Upgrade Video

27-Inch Late 2009 iMac Storage Upgrade Video

21.5-Inch Mid-2010 iMac Storage Upgrade Video

27-Inch Mid-2010 iMac Storage Upgrade Video (Primary Drive)

27-Inch Mid-2010 iMac Storage Upgrade Video (Secondary SSD)

21.5-Inch Mid-2011 iMac Storage Upgrade Video (Primary Drive)

21.5-Inch Mid-2011 iMac Storage Upgrade Video (Secondary SSD)

27-Inch Mid-2011 iMac Storage Upgrade Video (Primary Drive)

27-Inch Mid-2011 iMac Storage Upgrade Video (Secondary SSD)

From watching the videos, it should be clear that upgrading the storage in these models is rather challenging. If you do not feel comfortable -- or have the time -- to perform the upgrade yourself, it would be wise to hire a professional.

Hard Drive Upgrade Conclusion

Ultimately, it is possible to upgrade the hard drive in these 21.5-Inch and 27-Inch Aluminum iMac models or upgrade or install a secondary SSD in the "Mid-2011" 21.5-Inch models and "Mid-2010" and "Mid-2011" 27-Inch models, but opening the case is a challenge and it is definitely not for those without significant upgrade experience.

iMac Storage Purchase & Professional Installation Options

Quality storage is important. Be sure to buy from a quality vendor that sells storage with a reputation for reliability.

In the US (and many other countries), site sponsor Other World Computing sells SSDs for all iMac models as well as SSD Upgrade DIY Kits for easier do-it-yourself upgrades. The company also provides a "Turnkey" professional SSD upgrade service for many of these models.

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

In Australia, site sponsor Upgradeable sells iMac compatible hard drives and SSDs with fast shipping, a money-back guarantee, and more.

In New Zealand, site sponsor Upgradeable New Zealand sells iMac hard drives and SSDs with fast delivery to all corners of the country, precise compatibility, a lifetime warranty, and a money-back guarantee.

Also see:

• How do you upgrade the hard drive in the "Mid-2007," "Early 2008," "Early 2009" and "Mid-2009" (20-Inch and 24-Inch) Aluminum iMac models? What type of hard drive do they support? Can you swap the hard drive for an SSD?
• How do you upgrade the hard drive in the "Tapered Edge" Aluminum iMac models? What type of storage do they support? Is it possible to upgrade the hard drive or SSD?