Answer now (Can this 16GB memory module be used on my mid-2010 27' iMac? How many modules can be installed? Can slots be empty?) 1 Answer (Can this 16GB memory module be used on my mid-2010 27' iMac? How many modules can be installed? Can slots be empty?). I have upgraded the memory in my new 27' late 2013 iMac and it has been an interesting experience. When you have the iMac face down with the stand toward you, number the DIMM slots 1,2,3,4 with 1 nearest the base of the machine (amazingly, I have failed to find an illustration of which physical slots correspond to which Bank/DIMM slots. You can upgrade your Apple iMac 27-Inch (Late 2013) Computer to up to a maximum memory capacity of 32GB Memory. How many total memory slots to install memory? The Computer has 4 Sockets to install memory, already with 8GB(Removable) standard memory installed.

'Tapered Edge' Aluminum iMac Q&A

Update Published May 14, 2019

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How do you upgrade the RAM in the 'Tapered Edge' Aluminum iMac models? Is it even possible? What type of RAM do they use? How much RAM does each model actually support?

Please note that this Q&A explains how to upgrade the RAM in 'Tapered Edge' Aluminum iMac models that have RAM that can be upgraded. It also explains which of these models have RAM that cannot be upgraded. The 'Tapered Edge' Aluminium iMac models use model numbers A1418, A1419, A2115 and A2116.

EveryMac.com also provides RAM upgrade instructions for earlier Aluminum iMac models shipped from 2007 to 2012 -- both the 20-Inch and 24-Inch Aluminum iMac models (model numbers A1224 and A1225) and the 21.5-Inch and 27-Inch Aluminum iMac models (model numbers A1311 and A1312).

Regardless of year, the 'Tapered Edge' 27-Inch models have RAM that is easy to upgrade. The 21.5-Inch models, however, range from needlessly difficult to impossible when it comes to the RAM upgrade procedure.

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

Identification Help

There are critical differences between different 'Tapered Edge' iMac models. Different models use different types of RAM. Some models have RAM that is easy to upgrade, others are difficult to upgrade, and still others cannot be upgraded at all.

The 'Late 2012' through 'Mid-2017' 'Tapered Edge' iMac models all share the A1418 and A1419Model Numbers whereas the '2019' iMac models use newer A2116 and A2115 model numbers. Accordingly, more precise identifiers are crucial. For the purposes of upgrading the RAM, these models can be identified sufficiently by the Model Identifier in software and externally by EMC Number.

To locate the model identifier in software, select 'About This Mac' under the Apple Menu on your computer, click the 'More Info...' button, and finally click the 'System Report' button.

The EMC number is inconveniently located on the bottom of the 'foot' supporting the iMac, but EveryMac.com nevertheless has hand documented the EMC numbers as they are a unique external identifier.

More details about specific identifiers are provided in EveryMac.com's extensive Mac Identification section.

The relevant identifiers for these iMac models follow:

Tapered Edge iMac	Subfamily	Model ID	EMC No.
Late 2012
Late 2012
Late 2012
Late 2012
Late 2012
Late 2012
Early 2013
Late 2013
Late 2013
Late 2013
Late 2013
Late 2013
Late 2013
Mid-2014
Late 2014, 5K
Late 2014, 5K
Mid-2015, 5K
Late 2015
Late 2015
Late 2015, 4K
Late 2015, 4K
Late 2015, 5K
Late 2015, 5K
Late 2015, 5K
Mid-2017
Mid-2017, 4K
Mid-2017, 4K
Mid-2017, 4K
Mid-2017, 5K
Mid-2017, 5K
Mid-2017, 5K
Mid-2017, 5K
2019, 4K
2019, 4K
2019, 4K
2019, 5K
2019, 5K
2019, 5K
2019, 5K

EveryMac.com's Ultimate Mac Lookup feature -- as well as the EveryMac app -- also can identify these models by their Serial Numbers.

RAM Types & Actual Maximum RAM Capacities

For all of the 'Late 2012', 'Early 2013', 'Late 2013', and 'Late 2014' 21.5-Inch and 27-Inch 'Tapered Edge' iMac models, Apple formally notes that the systems have 'two 4 GB' of '1600 MHz DDR3 memory.' However, for the 27-Inch models, Apple adds that these systems have 'four user-accessible SO-DIMM slots.'

After the 'Late 2012' 21.5-Inch iMac models shipped, site sponsor Other World Computing disassembled one and discovered that it has two internal SO-DIMM slots (and subsequent 'Early 2013' and 'Late 2013' models are the same). Unfortunately, accessing these slots requires one to gingerly pry off the adhesive-attached display and remove the motherboard. By contrast, these 27-Inch models have a small panel that 'pops off' the back with the press of a button. Needless to say, pressing a button to access the four SO-DIMM slots in the 27-Inch models is quick and easy.

Sadly, for the 21.5-Inch 'Mid-2014' iMac -- the iMac 'Core i5' 1.4 21.5-Inch (Mid-2014) -- Apple notes that it has '8 GB of 1600 MHz LPDDR3 onboard memory.' OWC disassembled one and confirmed that the RAM is indeed soldered onboard and cannot be upgraded at all. This low-end model could not even be configured with more RAM at the time of initial purchase.

Likewise, the 21.5-Inch 'Late 2015' iMac models (even the more expensive 'Retina 4K' offerings), have a reported '8 GB of 1867 MHz LPDDR3 onboard memory' and OWC again confirmed that the RAM is soldered on these models. At the time of purchase, they could be upgraded to 16 GB for an extra US$200, but they cannot be upgraded at all after initial system purchase.

The 27-Inch 'Late 2015' iMac models support four 204-pin 1867 MHz PC3-14900 DDR3 SDRAM SO-DIMMs. Officially, Apple supports 32 GB of memory, but OWC has determined that 64 GB actually will work if the memory conforms to exacting standards.

For the 21.5-Inch 'Mid-2017' iMac models, Apple reports that they have 8 GB of '2133 MHz DDR4' or '2400 MHz DDR4' memory onboard. However, in a pleasant surprise, as first discovered by site sponsor OWC, the memory actually is not onboard and can be replaced or upgraded after the initial purchase of the Mac, it's just unnecessarily complicated. Some models actually can support more RAM than Apple officially supports, as well.

For the 27-Inch 'Mid-2017' iMac models, these systems have four easy-to-access 2400 MHz PC4-19200 DDR4 SDRAM SO-DIMMs (260-pin). Apple only formally supports 32 GB of RAM in the iMac 'Core i5' 3.4 27-Inch (Mid-2017), but it and all other 27' models from this line actually can support 64 GB of RAM.

For the 21.5-Inch '2019' iMac models, Apple reports that they have 8 GB of '2400 MHz DDR4' or '26666 MHz DDR4' memory 'built into the computer' and 'it can only be upgraded by an Apple Authorized Service Provider if you choose to upgrade at a later date.' In a teardown, site sponsor OWC determined that the RAM in this model actually is not built into the computer and it can be replaced or upgraded later, it's just a pain to disassemble the computer to do so.

Finally, the 27-Inch '2019' iMac models, like their predecessors, have four easy-to-access SO-DIMM slots. Unlike their predecessors, they use faster 2666 MHz PC4-21300 DDR4 DDR4 SDRAM SO-DIMMs (260-pin). Curiously, Apple formally allows up to 32 GB of RAM in the iMac 'Core i5' 3.0 27' 5K and up to 64 GB of RAM in the other '2019' iMac 5K models, but site sponsor OWC has determined that all of these models actually support up to 128 GB of RAM.

For your convenience, these details are summarized accordingly:

Apple Imac 27 Memory Slots