What are the differences between the "Late 2009" Aluminum iMac models?

Please note that the late "Late 2009" Aluminum iMac models have been discontinued. These models were replaced by the "Mid-2010" line on July 27, 2010.

Officially, there are four configurations that make up the "Late 2009" Aluminum iMac line, but the two configurations equipped with 21.5" displays vary only by hard drive and graphics options, so it's perhaps easiest to think of this line as consisting of three unique 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).

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

Both the 21.5" and 27" models use elegant "edge-to-edge" glass designs and "seamless all aluminum enclosures" (previous aluminum models have a modest aluminum border around the display and a black plastic back) with the entire computer tucked discreetly behind the flat-panel display.

The 21.5" and 27" models both are intended for use with 16:9 high-definition video and have "glossy" TFT active-matrix LED-backlit LCD displays with 1920x1080 and 2560x1440 native resolutions. Additionally, both displays are 8-bit and use IPS (In-Plane Switching) technology, which provides more accurate color even at wider viewing angles (178 degrees both horizontal and vertical). However, it is worth noting that the 27" models are brighter than the 21.5" models (375 cd/m2 compared to 320 cd/m2).

In keeping with the intent for high-definition video playback, the 21.5" and 27" models also have "redesigned" speakers mounted under the display that promise "louder, clearer sound with better bass response and less distortion". All have an integrated "iSight" video camera as well.

All of the "Late 2009" configurations were shipped with a compact aluminum Apple Wireless Keyboard and a then new multi-touch "Magic Mouse" where the "entire top is a seamless multi-touch surface" that allows one to "navigate using intuitive finger gestures". A then new aluminum remote was offered for an additional US$19 as well.

Connectivity is the same on all models -- with one notable exception -- and includes an SD card slot, four USB 2.0 ports, a Firewire "800" port, built-in AirPort Extreme (802.11a/b/g/n), Bluetooth 2.1+EDR, Gigabit Ethernet, a Mini DisplayPort (which supports an external display up to 30" - 2560x1600), and optical digital audio in and out ports. However, the 27" models also support input from external DisplayPort sources (so they can be used as an external display for another DisplayPort-equipped Mac, Blu-ray player, or other device).

Internally, all models support 16 GB of 1066 MHz PC3-8500 DDR3 SDRAM and have a 8X DL "SuperDrive", but have different graphics options and other configuration differences. The high-end "Core i5" 2.66 27-Inch (Late 2009) even has a different architecture with a "Direct Media Interface" (DMI) that "connects between the processor and chipset" in lieu of the 1066 MHz system bus.

Architecture and configuration differences are summarized below:

iMac "Late 2009"	3.06 x2 21.5"	3.06 x2 21.5"	3.06 x2 27"	2.66 x4 27"
Processor Speed:	3.06 GHz	3.06 GHz	3.06 GHz	2.66 GHz*
Processor Type:	Core 2 Duo	Core 2 Duo	Core 2 Duo	Core i5*
Processor Cores:	2	2	2	4*
Bus Speed:	1066 MHz	1066 MHz	1066 MHz	DMI*
L2 Cache:	3 MB	3 MB	3 MB	256k x4*
L3 Cache:	N/A	N/A	N/A	8 MB*
Hard Drive Size:	500 GB	1 TB	1 TB	1 TB
Standard RAM:	4 GB	4 GB	4 GB	4 GB
Video System:	9400M**	HD 4670†	HD 4670†	HD 4850††
Video Type:	Integrated**	GDDR3	GDDR3	GDDR3
Video Memory:	256 MB**	256 MB†	256 MB†	512 MB††
Optical Drive:	8X DL "SD"	8X DL "SD"	8X DL "SD"	8X DL "SD"
Display Size:	21.5-Inch	21.5-Inch	27-Inch	27-Inch
Native Resolution:	1920x1080	1920x1080	2560x1440	2560x1440
Brightness:	320 cd/m2	320 cd/m2	375 cd/m2	375 cd/m2
Video Input:	No	No	Yes	Yes
VESA Compliant:	No	No	Yes	Yes
Apple Order No:	MB950LL/A	MC413LL/A	MB952LL/A	MB953LL/A
Price:	US$1199	US$1499	US$1699	US$1999

* The high-end model is powered by a "Lynnfield/Nehalem" Intel "Core i5" processor with quad cores -- four independent processor cores on a single silicon chip. Each core has a dedicated 256k level 2 cache, shares 8 MB of level 3 cache, and has an integrated memory controller (dual channel). It has a a "Direct Media Interface" (DMI) that "connects between the processor and chipset" in lieu of a system bus. This model additionally could be configured with a 2.8 GHz "Core i7" processor (I7-860) for an additional US$200.

** This model has NVIDIA GeForce 9400M graphics which "shares" the memory with the system. The minimum graphics usage is 256 MB.

† By default, these models have an ATI Radeon HD 4670 graphics processor with 256 MB of dedicated GDDR3 memory. The 27-Inch model also could be custom configured with an ATI Radeon HD 4850 graphics processor with 512 MB of dedicated GDDR3 memory for an additional US$150.

†† This model has an ATI Radeon HD 4850 graphics processor with 512 MB of dedicated GDDR3 memory.

Ultimately, all of the "Late 2009" iMac models are solid choices for a desktop Mac and offer quality displays and solid performance. Whether the entry-level model with slower integrated graphics, the high-end model with its quad core processor, or something in between is best for your needs is a decision that only you can make.

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