What are all the differences between the "Late 2014/Mid-2015" Retina 5K Aluminum iMac models? What are all the differences between these models and the 27-Inch "Late 2013" iMac models? Which should I buy?

Please note that the "Late 2014" and "Mid-2015" iMac models have been discontinued. However, this Q&A has been updated subsequently and can be quite helpful to anyone buying or selling one of these systems on the used market.

There is only one stock "Late 2014" Retina 5K iMac model -- the iMac "Core i5" 3.5 27-Inch. However, because it can be uniquely identified, EveryMac.com also documents the custom processor option for the standard model independently as the iMac "Core i7" 4.0 27-Inch. On May 19, 2015, Apple added a cheaper "Mid-2015" Retina 5K variant -- the iMac "Core i5" 3.3 27-Inch. Both lines were replaced by the "Late 2015" models on October 13, 2015.

There are modest differences between the processor options for the "Late 2014" Retina 5K iMac models as well as minor differences between the "Late 2014" Retina 5K iMac models and their lower-end "Mid-2015" Retina 5K contemporary. There are much more substantial differences between the "Late 2014/Mid-2015" Retina 5K iMac and the previously introduced "Late 2013" iMac line.

Photo Credit: Apple, Inc. (Retina 5K iMac -- Front & Side)

Late 2014 Retina 5K iMac Differences

Both the standard iMac "Core i5" 3.5 27-Inch and the custom processor iMac "Core i7" 4.0 27-Inch are equipped with a Quad Core "Haswell" processor, but the processors differ accordingly:

iMac (Late 2014)	Core i5 3.5	Core i7 4.0
Specific Processor	I5-4690	I7-4790K
Clockspeed	3.5 GHz	4.0 GHz
Turbo Boost	3.9 GHz	4.4 GHz
Cores	4	4
Threads	4	8
L3 Cache	6 MB	8 MB

At the time of purchase, the Core i7 (4790K) processor option added US$250 to the cost of the standard Retina 5K iMac. As the custom processor provides roughly 14% faster performance in single core tasks and 38% faster performance in multicore tasks (where multithreading makes a significant difference), but only costs 10% more, the custom processor option was a good value.

Another notable custom configuration option is the graphics processor. By default, the "Late 2014" Retina 5K iMac is equipped with a 2 GB AMD Radeon R9 M290X graphics processor, but it also could be custom configured with a 4 GB AMD Radeon R9 M295X graphics processor for an extra US$250.

Mid-2015 Retina 5K iMac Differences

Compared to the also offered "Late 2014" iMac models, the "Mid-2015" iMac -- the iMac "Core i5" 3.3 27-Inch -- effectively is the same, but it has a slower processor, a slower graphics processor, and a comparatively slow hard drive instead of a faster "Fusion" Drive:

Retina 5K iMac	Late 2014 (3.5)	Mid-2015
Specific Processor	I5-4690	I5-4590
Clockspeed	3.5 GHz	3.3 GHz
Turbo Boost	3.9 GHz	3.7 GHz
Graphics Processor	Radeon R9 M290X	Radeon R9 M290
Storage	1 TB (Fusion)	1 TB 7200 RPM HD

The "Mid-2015" iMac model originally sold for US$300 less, also.

Late 2013 and Late 2014/Retina 5K iMac Differences

It would be easy to assume that the beautiful, high-resolution "Retina" display is the main difference between the 27-Inch iMac models from the "Late 2013" line -- the iMac "Core i5" 3.2 27-Inch, "Core i5" 3.4 27-Inch and "Core i7" 3.5 27-Inch -- and the also 27-Inch Retina 5K models -- the iMac "Core i5" 3.5 27-Inch, "Core i7" 4.0 27-Inch and "Core i5" 3.3 27-Inch.

The display is the most important difference. However, it is important to understand the specifics regarding the displays and worthwhile to understand other external, internal, and identification differences, too.

External Differences

For all practical purposes, the 27-Inch "Late 2013" and "Late 2014/Mid-2015" Retina 5K iMac models use the same all aluminum case design that sharply tapers to a 5 mm edge at both sides of the display.

The displays themselves are quite different, though. All of these lines have 16:9 LED-backlit TFT Active Matrix LCDs with IPS (In-Plane Switching) technology and have an "anti-reflective" coating over the glass. However, the 27-Inch "Late 2013" models have a 2560x1440 resolution whereas the "Late 2014/Mid-2015" Retina 5K models have a whopping 5120x2880 resolution running "pixel doubled" which results in a beautiful image with exceptional clarity.

All of these models additionally have an integrated 720p "FaceTime HD" webcam embedded in the upper display bezel, speakers integrated at the bottom edge of the display, and dual integrated microphones. None have an integrated optical drive, although an external one may be added at additional cost (site sponsor Adorama has the official external Apple SuperDrive for US$79 and Other World Computing has a variety of third-party external optical drive options).

Neither the "Late 2013" nor the "Late 2014/Mid-2015" Retina 5K lines are VESA compliant, but all could be configured with a wall mount option instead of the aluminum stand at the time of purchase for an additional US$40. If one of these iMac models was configured for wall mounting, it did not ship with the stand, and it cannot subsequently be reconfigured for traditional desk usage.

By default, each line ships with a notebook size aluminum wireless keyboard without a numeric keypad. However, Apple also offers a larger wired Apple Keyboard with a numeric keypad for the same price as a custom configuration option.

Apple also offers the choice of either the wireless "Magic Mouse" (which has the entire top as "a seamless multi-touch surface" that allows one to "navigate using intuitive finger gestures"), the "Magic Trackpad" (which provides multi-touch input like on a recent Apple notebook), or a "traditional" wired Apple mouse.

Connectivity Differences

There is one notable connectivity difference between the 27-Inch "Late 2013" and "Late 2014/Mid-2015" iMac models.

Each line has an SDXC-capable SD card slot, four USB 3.0 ports, one Gigabit Ethernet port (10/100/1000Base-T), one "headphone/optical digital audio output (minijack)" that also supports the Apple iPhone headset with microphone, and support for both 802.11ac Wi-Fi and Bluetooth 4.0.

However, the "Late 2013" iMac models have dual Thunderbolt ports whereas the "Late 2014/Mid-2015" iMac models have dual Thunderbolt 2 ports.

Identification Differences

At least when the display is turned off, the 27-Inch "Late 2013" and "Late 2014/Mid-2015" iMac models are virtually indistinguishable. These 27-Inch systems share model number A1419, too.

Consequently, the model number is not precise enough to uniquely identify specific models. However, as always, EveryMac.com has meticulously hand documented other details that are precise enough for identification.

Externally, the EMC Number is sufficiently unique for identification purposes. The 27-Inch "Late 2013" iMac models share EMC number 2639 whereas the "Late 2014/Mid-2015" Retina 5K models share EMC number 2806.

In software, the the 27-Inch "Late 2013" models are iMac14,2 whereas the "Late 2014/Mid-2015" Retina 5K models are iMac15,1.

Finally, EveryMac.com's Ultimate Mac Lookup feature additionally can uniquely identify each one of the "Late 2013" and "Late 2014/Mid-2015" Retina 5K iMac models by their serial numbers.

Internal Differences

Internally, the 27-Inch "Late 2013" and "Late 2014/Mid-2015" Retina 5K iMac models have some aspects in common, but there are important differences, too.

All of these lines use Quad Core "Haswell" processors mounted on LGA 1150 (Socket H3) processor sockets, have four easy to upgrade 1600 MHz PC3-12800 DDR3 SDRAM SO-DIMMs, and support both a 3.5" 6 Gb/s Serial ATA (Revision 3.0) hard drive or SSD and a PCIe-based "blade" SSD. By default, the "Late 2013" and "Mid-2015" Retina 5K models ship with a 1 TB hard drive whereas the "Late 2014" Retina 5K models ship with a faster 1 TB "Fusion Drive." It is possible to upgrade the storage in any of these models after the purchase of the system, although it is complicated.

The important internal differences are related to graphics capability. The 27-Inch "Late 2013" models have a 1 GB GeForce GT 755M or 2 GB GeForce GTX 775M graphics processor whereas the "Late 2014" Retina 5K models have a much faster default 2 GB AMD Radeon R9 M290X graphics processor driving a custom 60-pin eDP-based graphics interface. This custom graphics interface makes it possible for the graphics processor to power such a large display at up-to its native resolution of 5120x2880 with 24-bit color at a 60 Hz refresh rate.

The "Mid-2015" Retina 5K iMac uses the same custom graphics interface as the "Late 2014" Retina 5K iMac line, but it has a modestly slower 2 GB AMD Radeon R9 M290 graphics processor (rather than the M290X).

Comparison Chart

The major differences between the standard 27-Inch "Late 2013," "Late 2014" and "Mid-2015" Aluminum iMac models are summarized below. Please refer to the specs page for the model of interest for complete details:

	27" iMac (2013)	27" iMac (2014/5K)	27" iMac (2015/5K)
Processor Speed:	3.2 GHz, 3.4 GHz*	3.5 GHz**	3.3 GHz
Processor Type:	Quad Core i5*	Quad Core i5**	Quad Core i5
Processor Family:	Haswell	Haswell	Haswell
Standard RAM:	8 GB	8 GB	8 GB
Maximum RAM:	32 GB	32 GB	32 GB
RAM Upgrade:	Easy (Door)	Easy (Door)	Easy (Door)
Standard Storage:	1 TB (Hard Drive)	1 TB (Fusion)	1 TB (Hard Drive)
Standard Graphics:	GeForce GT 755M GeForce GTX 775M	Radeon R9 M290X	Radeon R9 M290
Dedicated VRAM:	1 GB (GDDR5) 2 GB (GDDR5)	2 GB (GDDR5)	2 GB (GDDR5)
Display Size:	27-Inch	27-Inch	27-Inch
Display Resolution:	2560x1440	5120x2880	5120x2880
Thunderbolt:	Dual (1.0)	Dual (2.0)	Dual (2.0)
Order Number (US):	ME088LL/A, ME089LL/A	MF886LL/A	MF885LL/A
EMC Number:	2639	2806	2806
Model Identifier:	iMac14,2	iMac15,1	iMac15,1
Orig. Price (US):	US$1799 US$1999	US$2499	US$1999
Orig. Price (UK):	£1599 £1749	£1999	£1599
Orig. Price (CA):	C$1849 C$2049	C$2749	C$2399
Orig. Price (AU):	A$2199 A$2449	A$2999	A$2799

* The standard 3.4 GHz configuration of the "Late 2013" model (ME089LL/A) was discontinued on May 19, 2015. This system originally could be configured with a 3.5 GHz Quad Core "Core i7" processor (I7-4771) for an extra US$200, as well. EveryMac.com also has documented this custom configuration as its own model.

** The "Late 2014" model additionally could be configured with a 4.0 GHz Quad Core "Core i7" processor (I7-4790K) for an extra US$250. EveryMac.com also has documented this custom configuration as its own model.

So, which one should I buy?

Just compared to one another, and not to newer models, whether to buy a high-resolution "Late 2014/Mid-2015" Retina 5K iMac or a "regular" resolution model from the "Late 2013" line largely comes down to whether or not you have the budget to purchase a Retina model and whether or not you can put its display to good use.

In hands-on evaluation, EveryMac.com found the "Retina 5K" display to be not only beautiful, but an exceptionally good value, as well. An equivalent display without a computer from Dell was advertised at the same price when the iMac Retina 5K was introduced. To be more competitive, Dell subsequently dropped the price, even before the company shipped its display, but the iMac Retina 5K remained an excellent value.

However, it is worth noting that those with less than the sharpest vision may find the difference between the regular and Retina displays to be unnoticeable, unnecessary, or at least not worth an extra money. Those interested in an iMac for high-end graphics work -- where precise color is important -- also may prefer to purchase a Mac Pro and a separate, even higher quality (or at least less glossy) display than the one provided by the Retina iMac.

Ultimately, if you have the funds to purchase an iMac "Retina 5K" and want a desktop computer, it is an excellent purchase. If money is an issue, earlier models -- which are even cheaper on the used market -- are well worth consideration, too.

New & Used iMac Purchase Options

There are many places to purchase a used iMac. However, purchasing from a solid company with many years of experience selling Macs -- and after sales support -- is the best option and will save you money and time, too.

In the US, site sponsor Adorama sells new iMac models with free shipping. Other World Computing and JemJem sell 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 also see EveryMac.com's Ultimate Mac Comparison feature to dynamically compare any iMac model to any other Mac.