What are all the differences between the "Mid-2017" Aluminum iMac models and the "Late 2015" models replaced?

Please note that all "Late 2015" and "Mid-2017" iMac models have been discontinued. However, this Q&A has been updated subsequently and can be quite helpful for anyone considering one of these models on the used market.

Although they look practically identical even with a fairly detailed inspection, there are important exterior and substantial interior differences between the "Late 2015" iMac models and the "Mid-2017" iMac models that replaced them.

As defined by EveryMac.com, the "Mid-2017" iMac models consist of the entry-level iMac "Core i5" 2.3 21.5"; the mid-range iMac "Core i5" 3.0 21.5" (4K) , "Core i5" 3.4 21.5" (4K), and "Core i7" 3.6 21.5" (4K); and the high-end iMac "Core i5" 3.4 27" (5K), "Core i5" 3.5 27" (5K), "Core i5" 3.8 27" (5K), and "Core i7" 4.2 27" (5K).

The "Late 2015" iMac models replaced consist of the entry-level iMac "Core i5" 1.6 21.5" and "Core i5" 2.8 21.5"; the mid-range iMac "Core i5" 3.1 21.5" (4K) and "Core i7" 3.3 21.5" (4K); and the high-end iMac "Core i5" 3.2 27" (5K), "Core i5" 3.3 27" (5K) and "Core i7" 4.0 27" (5K).

Photo Credit: Apple, Inc. (21.5" & 27" iMac Models)

Because the important differences typically are not obvious, and the "Mid-2017" iMac models are a significant improvement in many ways, a detailed comparison can be particularly useful.

External Differences

The 21.5-Inch and 27-Inch "Late 2015" and "Mid-2017" models use effectively the same all aluminum case design that tapers sharply to a 5 mm edge at the sides of the display and each have an integrated 720p "FaceTime HD" webcam in the upper display bezel, speakers integrated at the bottom edge of the display, and dual integrated microphones.

Although all of these displays have a glass cover with an anti-reflective coating, the displays in the "Mid-2017" 4K and 5K models are higher quality that the lower-end and earlier models alike.

The entry-level "Late 2015" and "Mid-2017" iMac models have a comparatively low resolution 21.5" 1920x1080 LED-backlit 16:9 widescreen IPS display.

The 21.5" 4K "Late 2015" iMac models have a higher-quality 21.5" 4096x2304 LED-backlit 16:9 widescreen IPS DCI-P3 "Retina 4K" display and the 27" 5K "Late 2015" models have a 27" LED-backlit 16:9 widescreen IPS DCI-P3 "Retina 5K" display with a gigantic 5120x2880 resolution.

Finally, the 21.5" 4K and 27" 5K "Mid-2017" iMac models have displays that are the same sizes and resolutions as their applicable predecessors, but they support an even wider color gamut of "one billion colors" and are much brighter with a brightness rating of 500 nits.

Connectivity Differences

Connectivity provided by the "Mid-2017" iMac models mostly is a substantial improvement to that offered by the "Late 2015" line.

All of these models have an SDXC-capable SD card slot, four USB 3.0 ports, one Gigabit Ethernet port (10/100/1000Base-T), and 802.11ac Wi-Fi.

However, the "Late 2015" models have two Thunderbolt 2 ports whereas the "Mid-2017" models have two Thunderbolt 3 (USB-C) ports that support higher resolution external displays.

More minor differences that are less likely to be critical to most users are that the "Late 2015" models have one "headphone/optical digital audio output (minijack)" that also supports the Apple iPhone headset with microphone and Bluetooth 4.0 whereas the "Mid-2017" models have a simple 3.5 mm analog headphone jack and Bluetooth 4.2.

Identification Differences

All of these iMac lines share Model Numbers. Specifically, the 21.5-Inch systems share model number A1418 and the 27-Inch systems share model number A1419. Consequently, these identifiers are not useful for most tasks.

However, these systems can be differentiated by Model Identifier in software and EMC Number externally. Just as the site has done for other Macs for more than two decades, EveryMac.com has meticulously hand documented these details for your convenience:

Tapered Edge iMac	Subfamily	Model ID	EMC No.
"Core i5" 1.6 21.5"	Late 2015	iMac16,1	2889
"Core i5" 2.8 21.5"	Late 2015	iMac16,2	2889
"Core i5" 3.1 21.5"	Late 2015, 4K	iMac16,2	2833
"Core i7" 3.3 21.5"	Late 2015, 4K	iMac16,2	2833
"Core i5" 3.2 27"	Late 2015, 5K	iMac17,1	2834
"Core i5" 3.3 27"	Late 2015, 5K	iMac17,1	2834
"Core i7" 4.0 27"	Late 2015, 5K	iMac17,1	2834
"Core i5" 2.3 21.5"	Mid-2017	iMac18,1	3068
"Core i5" 3.0 21.5"	Mid-2017, 4K	iMac18,2	3069
"Core i5" 3.4 21.5"	Mid-2017, 4K	iMac18,2	3069
"Core i7" 3.6 21.5"	Mid-2017, 4K	iMac18,2	3069
"Core i5" 3.4 27"	Mid-2017, 5K	iMac18,3	3070
"Core i5" 3.5 27"	Mid-2017, 5K	iMac18,3	3070
"Core i5" 3.8 27"	Mid-2017, 5K	iMac18,3	3070
"Core i7" 4.2 27"	Mid-2017, 5K	iMac18,3	3070

EveryMac.com's Ultimate Mac Lookup feature also can identify these iMac models by their serial numbers.

Internal Differences

Internally, the "Mid-2017" iMac models are a substantial upgrade from the "Late 2015" line that they replaced.

The 21.5-Inch and 27-Inch "Late 2015" iMac models use the Broadwell (5th Gen) and Skylake (6th Gen) Intel architectures, respectively, whereas the "Mid-2017" iMac models use a more advanced "Kaby Lake" (7th Gen) architecture with faster processors and memory.

There are many different graphics processors used by different models in the two lines, but in general, the newer line has faster graphics processors with more models that use dedicated VRAM rather than share system memory for video function.

One of the most major internal differences is that the 21.5-Inch "Late 2015" models have soldered RAM that cannot be upgraded at all after purchase whereas the 21.5-Inch "Mid-2017" models are a substantial improvement with RAM that can be upgraded, even if it is more difficult than it should be. The processors are socketed in the later models and soldered in the earlier ones, too.

All of the 27-Inch models in both lines offer RAM upgrades via a convenient door on the rear of the system. Processors are not easy to upgrade, but they are socketed and upgrades are possible.

Comparison Charts

The major differences between the 21.5-Inch "Late 2015" and "Mid-2017" Aluminum iMac models are summarized below. Please refer to the specs page for the model of interest for complete details.

21.5-Inch "Late 2015" & "Mid-2017" iMac Differences

	Late 2015	4K Late 2015	Mid-2017	4K Mid-2017
Processor Speed:	1.6, 2.8 GHz	3.1 GHz*	2.3 GHz	3.0, 3.4 GHz**
Processor Type:	Dual/Quad Core i5	Quad Core i5*	Dual Core i5	Quad Core i5*
Processor Family:	Broadwell	Broadwell	Kaby Lake	Kaby Lake
Processor Mounting:	Soldered	Soldered	LGA 1151	LGA 1151
RAM Type:	1867 MHz LPDDR3 SDRAM	1867 MHz LPDDR3 SDRAM	2133 MHz PC4-17000	2400 MHz PC4-19200
Standard RAM:	8 GB	8 GB	8 GB	8 GB
Maximum RAM:	16 GB†	16 GB†	16 GB	32 GB
RAM Slots:	None	None	2	2
RAM Upgrade:	Soldered	Soldered	Difficult	Difficult
Standard Storage:	Hard Drive	Hard Drive	Hard Drive	Hard Drive Fusion Drive
PCIe SSD Connector:	No	No	No‡	No‡
Standard Graphics:	HD Graphics 6000 Iris Pro 6200	Iris Pro 6200	Iris Plus 640	Radeon Pro 555/560
VRAM Type:	Integrated	Integrated	Integrated	Dedicated
Display Size:	21.5-Inch	21.5-Inch	21.5-Inch	21.5-Inch
Display Resolution:	1920x1080	4096x2304	1920x1080	4096x2304
Thunderbolt:	Dual (2.0)	Dual (2.0)	Dual (3)	Dual (3)
Bluetooth:	4.0	4.0	4.2	4.2
Order Number (US):	MK142LL/A MK442LL/A	MK452LL/A	MMQA2LL/A	MNDY2LL/A MNE02LL/A
EMC Number:	2889	2833	3068	3069
Model Identifier:	iMac16,1 iMac16,2	iMac16,2	iMac18,1	iMac18,2
Original Price (US):	US$1099 US$1299	US$1499	US$1099	US$1299 US$1499
Original Price (UK):	£899 £1049	£1199	£1049	£1249 £1449
Original Price (CA):	C$1399 C$1649	C$1899	C$1399	C$1729 C$1929
Original Price (AU):	A$1699 A$1999	A$2299	A$1599	A$1899 A$2199

* By custom configuration, the iMac "Core i5" 3.1 21.5" (4K) could be configured with a 3.3 GHz Quad Core "Core i7" processor (I7-5775R) for an extra US$200. EveryMac.com also has documented this custom configuration as its own model.

** By custom configuration, the iMac "Core i5" 3.0 21.5" (4K) and "Core i5" 3.4 21.5" (4K) could be custom configured with a 3.6 GHz Quad Core "Core i7" processor (I7-7700) for an extra US$300. EveryMac.com has documented this custom configuration as its own model, as well.

† In these models, 8 GB of RAM is onboard. They could be upgraded to 16 GB at the time of purchase as an optional upgrade for US$200. The RAM cannot be upgraded later at all.

‡ If these models were not configured with a "Fusion" Drive at the time of purchase, the PCIe connector for the SSD is not onboard and a second drive cannot be installed later. If they were configured with a "Fusion" Drive, this connector is onboard and occupied by the SSD.

27-Inch "Late 2015" & "Mid-2017" iMac Differences

The major differences between the standard 27-Inch "Late 2015" and "Mid-2017" Aluminum iMac models are summarized below. Please refer to the specs page for the model of interest for complete details:

	5K Late 2015	5K Mid-2017
Processor Speed:	3.2, 3.3 GHz*	3.4, 3.5, 3.8 GHz**
Processor Type:	Quad Core i5*	Quad Core i5*
Processor Family:	Skylake	Kaby Lake
Processor Mounting:	LGA 1151	LGA 1151
Standard RAM:	8 GB	8 GB
Maximum RAM:	64 GB	64 GB
RAM Slots:	4	4
RAM Upgrade:	Easy (Door)	Easy (Door)
Standard Storage:	Hard Drive, Fusion	Fusion
Standard Graphics:	Radeon R9 M380/M390 Radeon R9 M395	Radeon Pro 570/575/580
Dedicated VRAM:	2 GB	4 GB, 8 GB
Display Size:	27-Inch	27-Inch
Display Resolution:	5120x2880	5120x2880
Thunderbolt:	Dual (2.0)	Dual (3)
Bluetooth:	4.0	4.2
Order Number (US):	MK462LL/A MK472LL/A MK482LL/A	MNE92LL/A MNEA2LL/A MNED2LL/A
EMC Number:	2834	3070
Model Identifier:	iMac17,1	iMac18,3
Orig. Price (US):	US$1799 US$1999 US$2299	US$1799 US$1999 US$2299
Orig. Price (UK):	£1449 £1599 £1849	£1749 £1949 £2249
Orig. Price (CA):	C$2299 C$2599 C$2999	C$2399 C$2649 C$3079
Orig. Price (AU):	A$2799 A$3099 A$3599	A$2699 A$2999 A$3449

* The higher-end configuration of the iMac "Core i5" 3.2 (5K) 27-Inch (MK472LL/A) as well as the iMac "Core i5" 3.3 (5K) 27-Inch additionally could be configured with a 4.0 GHz Quad Core "Core i7" processor (I7-6700K) for an extra US$300 or US$250, respectively. EveryMac.com also has documented this custom configuration as its own model.

** The iMac "Core i5" 3.5 27" 5K and "Core i5" 3.8 27" 5K additionally could be custom configured with a 4.2 GHz Quad Core "Core i7" processor (I7-7700K) for an extra US$300 or US$200, respectively. EveryMac.com has documented this custom configuration as its own model, as well.

Comparison Summary

Ultimately, the "Mid-2017" iMac models represent not only a major step forward in terms of performance and connectivity, but also a welcomed return to a more upgradable design for the 21.5-Inch models.

The 21.5-Inch "Mid-2017" models are better than their predecessors in every way. The 27-Inch "Mid-2017" models also are a substantial improvement, but the 27-Inch "Late 2015" iMac line is easy to upgrade and these earlier models remain well worth consideration, also.

Please also see EveryMac.com's Ultimate Mac Comparison feature to dynamically compare any iMac model to any other Mac.

New & Used iMac Purchase Options

There are many places to purchase a used "Late 2015" or "Mid-2017" iMac. However, buying from a quality company with a solid track record in the Mac market will provide the best experience and save you money and time, too.

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.