What are the differences between the "Mid-2011" Aluminum iMac models? Which is best for my needs?

There are four stock "Mid-2011" iMac models, two with 21.5" displays -- the iMac "Core i5" 2.5 21.5" and "Core i5" 2.7 21.5" -- and two with 27" displays -- the iMac "Core i5" 2.7 27" and "Core i5" 3.1 27".

There also are two custom configurations available -- the iMac "Core i7" 2.8 21.5" and "Core i7" 3.4 27" -- which EveryMac.com has documented as their own models for reader convenience.

Photo Credit: Apple, Inc. ("Mid-2011" iMac -- 21.5" - Left, 27" - Right)

External Differences

All of the "Mid-2011" iMac models use elegant "edge-to-edge" glass designs and "seamless all aluminum enclosures" (essentially the same as those introduced by the "Late 2009" models and used by the preceding "Mid-2010" models as well) with the entire computer tucked discreetly behind the flat-panel display. Like previous lines, the 27" models are VESA compliant and can be easily wall-mounted whereas the 21.5" models are not VESA compliant and cannot be wall-mounted without ugly third-party hacks.

The 21.5" and 27" models both have glossy 8-bit 16:9 LED-backlit TFT Active Matrix LCDs that use IPS (In-Plane Switching) technology, which provides more accurate color even at wider viewing angles (178 degrees both horizontal and vertical). However, the 27" models are brighter than the 21.5" models. All have speakers mounted under the display and an integrated high-resolution "FaceTime HD" webcam with an ambient light sensor.

By default, all "Mid-2011" iMac configurations come with a compact aluminum wireless keyboard sans numeric keypad and the choice of either a wireless "Magic Mouse," where the "entire top is a seamless multi-touch surface" that allows one to "navigate using intuitive finger gestures" or a "Magic Trackpad" that provides multi-touch input like on a recent Apple notebook (both the "Magic Mouse" and "Magic Trackpad" can be purchased for an additional US$69). An aluminum remote is offered for an additional US$19 as well.

Connectivity Differences

Connectivity is the same on all "Mid-2011" iMac models -- with one significant exception -- and each includes an SDXC-capable SD card slot, four USB 2.0 ports, a Firewire "800" port, built-in 802.11a/b/g/n AirPort Extreme (which as first discovered by the now defunct HardMac unofficially supports up to 450 Mbit/sec "MIMO" 802.11n), Bluetooth 2.1+EDR, Gigabit Ethernet, and audio line in and out ports. However, the 21.5" models have a single Thunderbolt port whereas the 27" models have two Thunderbolt ports.

Each Thunderbolt port supports an external display up to 30" (2560x1600) as well as other peripherals that support the Thunderbolt standard. Thunderbolt provides a maximum theoretical throughput of 10 Gbps in both directions and supports as many as six devices "daisy-chained" together. The 21.5" iMac models can support one external display and the 27" iMac models can support two external displays simultaneously.

Thunderbolt is backwards compatible with Mini DisplayPort-equipped monitors and works with DVI, VGA, dual-link DVI and HDMI adapters as well. As first reported by MacWorld, both the 21.5" and 27" models support "Target Display Mode" from external Thunderbolt-equipped sources (so they can be used as an external display from another Thunderbolt-equipped Mac -- like the "Early 2011" MacBook Pro line -- but not with older Mini DisplayPort-equipped Macs).

Identification Differences

Externally, the "Mid-2011" iMac line unfortunately uses the same A1311 and A1312 model numbers as earlier iMac models that share the same case, but they can be spotted by the unique EMC numbers of 2428 and 2429 (inconveniently located under the "foot" supporting the system), for the 21.5" and 27" models, respectively.

In software, the 21.5" and 27" models are assigned model identifiers of iMac12,1 and iMac12,2. When either the EMC number or model identifier are combined with processor speed, it is possible to pinpoint the exact model. Alternately, you can type the serial number into EveryMac.com's Ultimate Mac Lookup potentially for an exact match.

Internal Differences

Internally, by default, all "Mid-2011" iMac models use "Sandy Bridge" Core i5 Quad Core processors mounted on an LGA 1155 (H2) processor socket, but can be custom configured with a Quad Core Core i7 processor as well. Each also has a "Direct Media Interface" (DMI) that "connects between the processor and chipset" in lieu of a traditional system bus that Intel reports runs at 5 GT/s.

Officially, all support up to 16 GB of 1333 MHz PC3-10600 DDR3 SDRAM, but site sponsor OWC has found that the 21.5-Inch and 27-Inch models actually are capable of supporting up to 32 GB of RAM. As also discovered by OWC, as shipped, these models only supported the 3 Gb/s Serial ATA 2.0 standard, but the iMac EFI Update 1.6, released two days later, quietly provided faster 6 Gb/s Serial ATA 3.0 support for the hard drive/SSD (the optical drive still uses a slower 3 Gb/s Serial ATA 2.0 connector). All but the entry-level iMac "Core i5" 2.5 21.5" model can be custom configured with an SSD at the time of purchase in addition to a hard drive. With some effort, an SSD can be installed after purchase in these models as well.

Comparison Chart

The major differences between the stock "Mid-2011" 21.5" and 27" iMac models -- size, display, connectivity, processor speed and graphics -- as well as configuration, identifiers, and price -- are summarized below:

* By custom configuration, the iMac "Core i5" 2.7 21.5" can be configured with a 2.8 GHz Quad Core "Core i7" processor (I7-2600S) for an additional US$200. This "Core i7" processor supports Hyper-Threading (it has two threads per core for a total of eight threads for the system), Turbo Boost 2.0 (the system can dynamically increase the processor clockspeed to 3.8 GHz when tasks demand), and a larger 8 MB level 3 cache, too.

** The iMac "Core i5" 3.1 27" also can be configured with a 3.4 GHz Quad Core "Core i7" processor (I7-2600) for an additional US$200. This "Core i7" processor supports Hyper-Threading (it has two threads per core for a total of eight threads for the system), Turbo Boost 2.0 (the system can dynamically increase the processor clockspeed to 3.8 GHz when tasks demand), and a larger 8 MB level 3 cache, too.

† By custom configuration, this model also can be upgraded to 2 GB of dedicated GDDR5 video memory for an additional US$100.

So, which is best for my needs?

To determine which "Mid-2011" iMac is best for your needs, it is first important to identify which aspect of the purchase is most important to you. Differences between models in the "Mid-2011" line are less substantial than they were for earlier lines, and this may make the decision more difficult.

Nevertheless, if price is the most important consideration, buy the least expensive iMac "Core i5" 2.5 21.5" model. Alternately, it may be even better for you to consider a used iMac model at an even lower price. Depending on your needs, a new or used Mac mini and an external display also could cost less than a new Aluminum iMac or a recent used Aluminum iMac.

If performance is most important -- and expansion is not that important and price is no object -- the high-end iMac "Core i5" 3.1 27" or the even faster custom configured iMac "Core i7" 3.4 27" are the models to consider. Those interested in performance and expansion should instead consider a Mac Pro.

The differences between remaining models are more nuanced. The lower-end 27" model -- the iMac "Core i5" 2.7 27" -- has a processor that is 15% slower in raw clockspeed (as well as a slower graphics processor), but costs roughly 18% less than the high-end model, so for one interested in a 27" display, but more concerned with price than performance may find it to be a good value.

The higher-end 21" model -- the iMac "Core i5" 2.7 21.5" -- has performance roughly equivalent with the lower-end 27" model -- the iMac "Core i5" 2.7 27" -- but costs roughly 12% less. For one who values performance more than a large display (or finds the 27" display too big, period), this could be the model to pick. The custom configured 21.5" model -- the iMac "Core i7" 2.8 21.5" -- is even faster than the 27" model, but costs the same price, and also is well worth consideration by anyone who values performance and price over display size.

Ultimately, any of the "Mid-2011" iMac models would be a good choice for a desktop Mac and offer quality displays and solid performance. By evaluating which aspect of the purchase is most important to you and the options above, it is hoped that you can make an excellent choice for your needs.

In the US, site sponsor Adorama sells new iMac models with free shipping. Other World Computing sells used and refurb iMac models at bargain prices with free shipping, as well. Finally, if you need to sell an iMac, A+ BBB-rated Cash for Your Mac will buy your older iMac with an instant quote and prompt payment.

In the UK, site sponsor Hoxton Macs sells used iMac models with a one-year warranty and free next day delivery throughout the UK. Delivery across Europe also is available starting at just £9.99 for two-day delivery to France and Germany.

In Australia, site sponsor Mac City likewise has a variety of used iMac models sold at low prices and available with a free warranty and fast shipping across Australia.

Please refer to EveryMac.com's Ultimate Mac Comparison feature to dynamically compare any iMac model to any other G3 or later Mac.