What are all the differences between the "Late 2013" Aluminum iMac models? Which is best for me?

Please note that the "Late 2013" 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.

With the 21.5-Inch and 27-Inch "Late 2013" Aluminum iMac models sitting side-by-side, it would be easy to assume that these systems are differentiated mostly by screen size.

Display size is one important difference between the 21.5-Inch models -- the standard iMac "Core i5" 2.7 21.5-Inch and "Core i5" 2.9 21.5-Inch, and CTO "Core i7" 3.1 21.5-Inch -- and the 27-Inch models -- the standard iMac "Core i5" 3.2 27-Inch and "Core i5" 3.4 27-Inch and CTO "Core i7" 3.5 27-Inch -- but there also are other substantial differences that are not obvious to the naked eye.

Photo Credit: Apple, Inc. (21.5" & 27" Tapered Edge iMac, Left & Right, Respectively)

External Differences

All of the "Late 2013" iMac systems have a completely aluminum case design that sharply tapers to a 5 mm edge at the sides of the display. As shipped standard, neither the 21.5-Inch or 27-Inch models are VESA compliant, but both sizes can be configured with a VESA mount option instead of the aluminum stand at the time of purchase.

The 21.5-Inch and 27-Inch systems both have "anti-reflective" 8-bit 16:9 LED-backlit TFT Active Matrix LCDs with different native resolutions -- 1920x1080 and 2560x1440, respectively. Both use IPS (In-Plane Switching) technology, which provides more accurate color than displays without IPS and each have a glass cover that is fully laminated to the LCD itself. This lamination means that reflections are reduced, but it also means that the display and the glass only can be replaced as a single piece which is more costly and potentially wasteful, as well.

Both sizes 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. Neither has 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).

By default, every "Late 2013" iMac includes a notebook size aluminum wireless keyboard without a numeric keypad and the choice of either the wireless "Magic Mouse" (which has the "entire top is 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 (or Lack Thereof)

Connectivity is identical on all "Late 2013" iMac models.

All of these systems have an SDXC-capable SD card slot, four USB 3.0 ports, two Thunderbolt ports -- which support Mini DisplayPort output for two external displays up to 30" (2560x1600) as well as "Target Display Mode" via Thunderbolt -- one Gigabit Ethernet port (10/100/1000Base-T), and one "headphone/optical digital audio output (minijack)" that also supports the Apple iPhone headset with microphone.

The "Late 2013" iMac systems also support 802.11ac Wi-Fi, which is backwards compatible with the slower 802.11a/b/g/n standards, as well as Bluetooth 4.0.

Identification Differences

The "Late 2013" iMac models share model numbers with the previous "Late 2012" iMac line. Specifically, these 21.5-Inch models share model number A1418 and these 27-Inch models share model number A1419.

Consequently, the model numbers are not adequately unique for most tasks, such as upgrading the RAM and other identifiers are better for more precision.

Externally, the EMC number is best as it is less likely to be shared by future models using the same case type. The Iris-equipped entry-level iMac "Core i5" 2.7 21.5-Inch is EMC number 2638 and the iMac "Core i5" 2.9 21.5-Inch and "Core i7" 3.1 21.5-Inch models with dedicated graphics are EMC number 2742. All 27-Inch "Late 2013" iMac models share EMC number 2639.

In software, the "Late 2013" 21.5-Inch iMac models are Model Identifier iMac14,1 and iMac14,3 (again, for the entry-level model with Iris graphics and the higher-end models with dedicated graphics, respectively), and the 27-Inch models are iMac14,2.

Just as the site has for other models for many years, EveryMac.com has meticulously hand documented all of these details for your convenience.

Finally, EveryMac.com's Ultimate Mac Lookup feature additionally can uniquely identify each one of the "Late 2013" iMac models by their serial numbers.

Internal Differences

By default, all "Late 2013" iMac models use "Haswell" Core i5 Quad Core processors, but some models can be custom configured with a Quad Core Core i7 processor, as well. Regardless of the processor configuration, the "Haswell" architecture uses a directly attached "On Package Interface" (OPI) instead of the earlier "Direct Media Interface" (DMI) or traditional system bus to connect between the processor and chipset.

There is a major processor difference between the 21.5-Inch and 27-Inch models other than clockspeed, though. As first discovered by iFixit, the processor in the 21.5-Inch models is soldered to the motherboard and cannot be upgraded whereas the processor in the 27-Inch models is mounted on an LGA 1150 (H3) processor socket and can be upgraded after purchase by a technically savvy individual.

The graphics also are quite different, particularly between the entry-level iMac "Core i5" 2.7 21.5-Inch model which uses "integrated" Intel Iris Pro 5200 graphics and the other models, which use NVIDIA GeForce GT/GTX graphics of differing capability with dedicated GDDR5 memory of varying capacity.

Both the 21.5-Inch and 27-Inch "Late 2013" models support 204-pin 1600 MHz PC3-12800 DDR3 SDRAM SO-DIMMs, although the 21.5-Inch models only have two RAM slots and support 16 GB of RAM whereas the 27-Inch models have four RAM slots and support 32 GB of RAM. Officially, Apple does not intend for one to upgrade the RAM in the 21.5-Inch models after initial purchase at all -- and doing so is unnecessarily complicated -- but it is possible. The 27-Inch models, by contrast, have a "pop off" door on the rear that makes upgrading the RAM quick and easy.

Regardless of display size, the "Late 2013" models all have a Serial ATA (6 Gb/s) connector for a hard drive as well as a proprietary PCIe connector for an SSD. If the SSD is not installed at the time of purchase, the connector still is present and later professional or self-installation is possible. It is possible to upgrade the hard drive and/or SSD on all of these systems, but it is not easy.

Comparison Chart

The major differences between the four stock "Late 2013" 21.5" and 27" iMac models -- size, display, processor, processor mounting, graphics, and RAM upgrade methods -- as well as configuration, identifiers, and price -- are summarized below:

iMac "Late 2013"	2.7 21.5"	2.9 21.5"	3.2 27"	3.4 27"
Std. Processor Speed:	2.7 GHz	2.9 GHz*	3.2 GHz	3.4 GHz**
Std. Processor Type:	Core i5	Core i5*	Core i5	Core i5**
Std. Processor No:	4570R	4570S*	4570	4670**
Std. Processor Cores:	4	4	4	4
Turbo Boost:	3.2 GHz	3.6 GHz	3.6 GHz	3.8 GHz
Hyper-Threading:	No	No*	No	No**
Processor Mounting:	Soldered	Soldered	LGA 1150	LGA 1150
L2 Cache:	256k x4	256k x4	256k x4	256k x4
L3 Cache:	6 MB	6 MB*	6 MB	6 MB*
Std. Hard Drive:	1 TB (5400)	1 TB (5400)	1 TB (7200)	1 TB (7200)
Std. RAM:	8 GB	8 GB	8 GB	8 GB
Max. RAM:	16 GB	16 GB	32 GB	32 GB
RAM Upgrade:	Difficult (Hack)	Difficult (Hack)	Easy (Door)	Easy (Door)
Video System:	Iris Pro 5200†	GT 750M	GT 755M	GTX 775M††
Video Type:	Integrated†	GDDR5	GDDR5	GDDR5
Video Memory:	1 GB (Shared)†	1 GB	1 GB	2 GB††
Optical Drive:	None	None	None	None
Display Size:	21.5-Inch	21.5-Inch	27-Inch	27-Inch
Native Resolution:	1920x1080	1920x1080	2560x1440	2560x1440
Apple Order No (US):	ME086LL/A	ME087LL/A	ME088LL/A	ME089LL/A
Apple Model ID:	iMac14,1	iMac14,3	iMac14,2	iMac14,2
EMC Number:	2638	2742	2639	2639
Original Price (US):	US$1299	US$1499	US$1799	US$1999

* By custom configuration, the iMac "Core i5" 2.9 21.5-Inch could be configured with a 3.1 GHz Quad Core "Core i7" processor (I7-4770S) for an extra US$200. The "Core i7" processor supports Hyper-Threading (it has two threads per core for a total of eight threads for the system) as well as Turbo Boost 2.0 (the system can dynamically increase the processor clockspeed to 3.9 GHz when tasks demand). It has a larger 8 MB level 3 cache, too. EveryMac.com also has documented this custom configuration as its own model.

** The iMac "Core i5" 3.4 27-Inch could be configured with a 3.5 GHz Quad Core "Core i7" processor (I7-4771) for an extra US$200. This "Core i7" processor supports Hyper-Threading (it has two threads per core for a total of eight threads for the system) as well as Turbo Boost 2.0 (the system can dynamically increase the processor clockspeed to 3.9 GHz when tasks demand). It has a larger 8 MB level 3 cache, as well. EveryMac.com also has documented this custom configuration as its own model.

† The Intel Iris Pro 5200 graphics processor shares 1 GB of memory with the system for graphics function, but it also has 128 MB of "Crystalwell" embedded DRAM on the CPU package to provide more memory bandwidth than earlier integrated graphics solutions.

†† At the time of purchase, this model could be custom configured with a NVIDIA GeForce GTX 780M with 4 GB of dedicated GDDR5 memory for an extra US$150.

So, which is best for my needs?

As the above detailed comparison demonstrates, the 21.5-Inch and 27-Inch "Late 2013" iMac models are quite similar to one another in many respects. Although these models are no longer new, you may still be interested in choosing between them on the used market.

Just compared to one another, you essentially will have to decide if a larger display, easy RAM upgrades and more RAM capacity (and the possibility of a CPU upgrade), as well as faster performance are worth the higher upfront price of the 27-Inch models. Of course, with the option of easily expanding the RAM to at least 32 GB later, the 27-Inch models also likely will remain usable for longer, which makes them a better buy over the long term for one who does not replace his or her computer on an annual or semi-annual basis.

If upfront price is the primary concern, the iMac "Core i5" 1.4 21.5-Inch is cheapest, albeit it is a lot slower than the "Late 2013" models and has soldered RAM (which will limit its lifespan). Otherwise, the basic iMac "Core i5" 2.7 21.5-Inch is the cheapest option remaining among these models.

If you want a big display and a high performance all-in-one Mac, but the higher-end Retina 5K models are too expensive or you find the higher-resolution display unnecessary, the iMac "Core i5" 3.2 27-Inch is the remaining option among these models.

The middle 21.5-Inch options, representing more of a balance between price-and-performance present a more difficult decision, but are particularly worth evaluating accordingly.

If physical space and dedicated graphics are important to you, the higher end 21.5-Inch model -- the iMac "Core i5" 2.9 21.5-Inch -- is worth consideration. At the time it was released, it cost 15% more (US$200) than the entry-level model and only provides roughly 7% more clockspeed, but the dedicated graphics may provide more performance for some tasks. It's still a hassle, or even impossible, to upgrade, though.

The entry-level 27-Inch model -- the iMac "Core i5" 3.2 27-Inch -- is not only faster, but provides a bigger display, better graphics, and easy to upgrade RAM as well as more RAM capacity and the possibility of a CPU upgrade. At the time it was released, these benefits cost an additional US$300. On the used market, the price difference may vary, but EveryMac.com would encourage you to buy a 27-Inch model if you can afford the upfront price it as it likely will be usable for longer and cost less over the course of its usable life as a result.

Compared to the higher-end 27-Inch model -- the iMac "Core i5" 3.4 27-Inch -- the entry-level 27-Inch system is a better choice for many, as it originally cost 10% less than the high-end model when it was new, but is only about 4% slower overall (with the exception of graphics, as the high end model has a considerably faster graphics processor). Consequently, the entry-level 27-Inch model is a good choice for anyone interested in a solid price-to-performance option.

Ultimately, a 27-Inch "Late 2013" iMac model is a better choice for anyone interested in display size, performance, and upgrades than a 21.5-Inch model. For those more interested in price, the 21.5-Inch models are worth consideration, but older models are cheaper still and many have easy to upgrade RAM, as well.

New & Used iMac Purchase Options

There are many places to purchase a used "Late 2013" 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.