Crucial CT2K16G4S266M 32 GB Kit (16 GB x2) (DDR4, 2666 MT/s

Crucial RAM 16GB Kit (2x8GB) DDR4 2400MHz CL17 Laptop Memory CT2K8G4SFS824A

Crucial CT2K16G4S266M 32 GB Kit (16 GB x2) (DDR4, 2666 MT/s, PC4-21300, CL19, Dual Rank x8, SODIMM, 260-Pin) Memory for Mac, Gree


Crucial DDR4 iMac SODIMMsodimm iMacspeedquality

Reliability for Mac systems

When you use your Mac system, you expect intuitive, dependable performance. Expect the same out of your memory. Every Crucial module that leaves our doors has been tested at the component level for voltage and temperature resistances, signal integrity, and software compatibility.

Speed for Mac systems

A memory upgrade is the fastest, easiest, and most affordable way to get more performance out of your Mac system. Upgrade your Mac with Crucial memory modules and maximize your creativity with top speed and high density DDR3 and DDR4 memory modules

Support for Mac systems

Unsure how to install memory or have an important question about your Mac system? Let the Crucial experts help! They know Apple systems inside and out and enjoy providing helpful, friendly technical support. Whether it’s phone support, videos, FAQ articles, or do-it-yourself install guides for more than 70 different Mac systems, Crucial has the resources you need to keep your system up to speed.

Micron quality – A higher level of reliability

As a brand of Micron, one of the largest memory manufacturers in the world, Crucial memory for Mac systems is backed by the same quality and innovation that has produced some of the world’s most advanced memory and storage technologies. With a product portfolio that includes upgrades for more than 100,000 systems, we’ve got one specifically designed for your Mac system.



Weight: 9.07 g
Dimensions: 6.86 x 0.51 x 2.79 cm; 9.07 Grams
Brand: Crucial
Model: CT2K16G4S266M
Colour: Green
Batteries Included: No
Manufacture: Crucial
Dimensions: 6.86 x 0.51 x 2.79 cm; 9.07 Grams

44 Responses

  1. Anonymous says:

     United Kingdom

    I wanted to add extra RAM to my 27″ IMac 2020 these are perfect!

  2. Anonymous says:

     United Kingdom

    I always purchase my Mac Memory from Crucial as they provide great service and great prices.

  3. FHXPatrice says:

     United Kingdom

    Golden Review Award: 2 From Our UsersBought to upgrade my iMac 27″ 5K 2019 3GHz 6-Core Intel Core i5 from 8GB to 32GB as I’ve started to do more video editing and my machine was struggling a bit while using Adobe After Effects.

    Easiest installation ever, worked perfectly as soon as I turned the machine on.

    It feels a lot less sluggish now. I have opened InDesign, Illustrator and Photoshop at the same time (something the machine used to struggle with) and opened various large working files. I can flick between all 3 programs a lot smoother than I used to.

    Very very happy with my purchase.

  4. JasmineCooke says:

     United Kingdom

    Works perfectly with Apple hardware. I’ve bought two separate kits and the computer has recognised the full 128GB. No prohlem whasoever.

  5. Anonymous says:

     United Kingdom

    Have used Crucial before and they are just brilliant. Such an affordable way to increase your RAM, instead of paying eye watering Apple prices. Just look up your computer specs on their website and you can find the RAM you need. So easy to install, a child could do it. Just remember to touch something to ground yourself prior to installation, so you get rid of any unwanted static while you complete the operation. Have updated all my Macs by using their RAM. Never had a problem, so happy to recommend. Quick delivery and always reliable.

  6. Anonymous says:

     United Kingdom

    Golden Review Award: 2 From Our UsersThese were bought to upgrade the memory of a 2020 27″ iMac from 8gb to 64gb. I decided to remove the existing memory as I wasn’t sure about compatibility with speed and thought an extra 8gb is not going to make a lot difference since I’m sticking 64gb in.

    There is an easy to remove cover at the back of the iMac, a couple of springy clips allow you to move the memory carriage into an accessible position. The old memory just lifts out and the new memory slotted in the same place. It took longer to remove all the connections at the back of the computer than it did to replace the memory modules.

    If you need to check what memory is in your iMac click on the Apple (top Left), select About then select memory and a graphic shows you what memory modules you have and which slot they are in. Slots 1 & 3, and slots 2 & 4 are paired and need the same memory modules in each one of the pair, though 1 & 3 can have different RAM values from 2 & 4. So I put each of these two 32gb modules in slot 1 and slot 3.

    When I turned everything back on the iMac worked as if nothing had happened, but I ran a Photoshop test that was taking 4 minutes with 8gb RAM. It was now almost instant with the 64gb RAM upgrade, so I’m very pleased with my purchase.

  7. Anonymous says:

     United Kingdom

    As an old school graphic designer that uses Adobe CC software for print and digital, I’ve always been on the lifelong learning curve with tech that is several steps/planes ahead of where I am right now. Most of the time this does not inhibit my day to day use of the main software tools but having speced my Apple desktop Mac with the maximum RAM capability I found that in the age of remote working and being networked so much of the time that this phenomenon more than anything slows down the machine when my broadband connection becomes not so broad after all.
    The moral of this story is that to get the best out of this product is to be offline as much as possible.

  8. KristianCrensha says:

     United Kingdom

    Ningn problema al instalar solo tener cuidado que estn bien fijas las memorias en una Mac mini 2018

    5.0 out of 5 stars Excelente todo ok 100 % compatible Max Mini 2018

  9. Anonymous says:

     United Kingdom

    Good product. Needed to get this correct as it’s my work computer. Don’t mess about trying to get cheaper unbranded memory. Get the proper stuff as it works.

  10. Anonymous says:

     United Kingdom

    First time ordering Crucial from Amazon but seems the same stuff.. fitted and working ok

  11. Anonymous says:

     United Kingdom

    I bought this RAM as I wanted a single 32GB DDR4 SODIMM stick for my new Framework laptop (DIY Edition i5) and it was ~20 cheaper than the equivalent non-Mac sticks. Contrary to the ‘official’ answer to a question about using this in a non apple device – it works fine, as it’s standard DDR4 SODIMM. Full 32GB detected and usable by Fedora on my laptop, no issues. I wouldn’t use non-Mac RAM in Macs however as they can be very fussy about tolerances and error checking.

    Great value - Ignore marketing, not only for Mac, works fine in Framework Laptop

  12. Anonymous says:

     United Kingdom

    Bought for a Mac to increase ram considerably cheaper than getting proprietary product from manufacturer.

  13. CatheriDuigan says:

     United Kingdom

    Bit of,a bargain at this price, (125), bought to upgrade a recently purchased iMac.
    Went from 16 to 40Gb and notice a lot of difference. Start up times appear to have reduced and no slowing or spinning beach ball when having numerous windows open.

    I use proprietary structural engineering software running under windows 10 in a virtual environment (parallels) with native Mac AutoCAD, as well as MS office and a other bits and pieces.

    Since upgrading I can run a windows on one screen and a Mac screen without any loss of speed, brilliant.

    Excellent value and a brilliant, simple upgrade.

  14. Anonymous says:

     United Kingdom

    This is the only non-Apple memory that will work in a 128 GB configuration in an iMac.
    I have verified this in a professional motion picture production environment over a year.
    Other brand memory in a 128 GB configuration will produce multiple crashes every day!

  15. Bree Fowler says:

     United Kingdom

    I bought a 2020 iMac 27″ but was astounded at the price for RAM upgrades – so after a bit of a web search I found this as a viable RAM upgrade option.

    I was not disappointed in any way at all – it took me literally 2 minutes to install this and my Mac now runs like the powerhouse it should do, at a fraction of the cost that I would have paid if I had bought this direct.

    If you have upgradable RAM options in your Mac, do this now! I can now run GPU-intensive activities like photoshop and indesign in a flash and they run simultaniously without any lag whatsoeve

  16. Josh says:

     United Kingdom

    Golden Review Award: 3 From Our UsersHaving recently purchased one of the last 2020 27″ iMacs from Amazon I thought it best to future-proof it as best I can, so purchased some additional RAM for it bearing in mind it only had 8GB, so purchased this Crucial CT2K16G4S266M 32 GB Kit which consists of 2 off 16GB DDR4 2666 Ram chips.

    Unlike the smaller 21.5″ iMac and some of the newer models, the Ram in the 2020 27″ iMac can be easily upgraded, and yes I can confirm that it’s very easy to do and has resulted in the RAM going from a paltry 8GB to a far more impressive 40GB because the old RAM chips can be retained.

    Sure the new iMacs are coming out, but they seem to be missing ports on the back, and realistically I’m not going to be rendering 5K videos for the foreseeable future, mainly YouTube, emailing, and some photo editing, so have purchased Affinity photo editing software so am well sorted.

    This has to be one of the easiest fixes to speed up your computer and will future-proof it for many years. The Crucial RAM upgrade has to be one of the best buys at the moment, and aside from changing the HDD to SSD or using an external SSD to store your files on if you have a tiny internal SSD drive there aren’t really a lot of other steps you can take to make your computer run faster.

    Highly recommended if you have a 2020 (or older) 27″ iMac and want to speed it up a bit.

  17. Jacinto02Q says:

     United Kingdom

    I purchased a iMAC 27inch 5k 2020, with 8gb Ram installed, purchased 2 x 8gb to take me to 24gb I’m not a gamer but a 62 yr old female geek! figured I’d upgrade it so the setup will last me a while.
    it was a breeze to install.
    if i can install it anyone can!

  18. Anonymous says:

     United Kingdom

    Over the years I have always gone for Crucial memory upgrades because of the guaranteed quality and reliability. I bought this to upgrade my Retina 5K, 27″, 2020 iMac with its 3.8 Ghz 8-core Intel i7 processor. At restart the iMac immediately recognised the memory, giving me 40 Gb. Happy days …….

  19. Anonymous says:

     United Kingdom

    I got this for my iMac 2020 5k 27″. It took me less than 5 minutes to install and works perfectly. It has really reduced the memory pressure in the activity monitor. I removed the existing sticks and put the new ones in the original slots. 32 GB might be a bit overkill for for the music production that I do but it’s there if I need it. I would definitely recommend this product.

  20. ThelmaGarza says:

     United Kingdom

    If you use Apple computers you’ll know that they charge exorbitant prices for RAM which has to be installed by their technicians on most (but not all) of their computers. It’s why I bought an Apple iMac, a rare exception for which you can easily buy your own RAM (from Crucial) to install yourself without voiding your warranty. Apple would charge me 600 for 32GB of this RAM whereas Crucial will sell me exactly the same Apple approved 32GB of RAM for 140.

  21. Anonymous says:

     United Kingdom

    Used to add 32Gb (2 x 16Gb modules) memory on a new iMAC and used in conjunction with 16Gb pre-installed Apple memory.

    Works perfectly. I have used Crucial memory modules on MACs for many years and they have always been straightforward to install and reliable. They are very much cheaper than Apple’s.

  22. MariaKemper says:

     United Kingdom

    o dislikes. not the cheapest but neither too expensive. have used crucial since I first bought my first pc. have used apple for last 12 years. no failures in all the time. don’t know what sheerness means ??

  23. Anonymous says:

     United Kingdom

    Thank you Amazon and MoreFrom for this set . It works like a charm!
    Payed a bit more than the standard Mac RAM offers on here, but it was worth it.

  24. Anonymous says:

     United Kingdom

    I was very sceptical about upgrading the memory on my beloved iMac, but took the plunge after new year as this was my resolution to fix it. It was becoming unbearable slow and unresponsive to typing and general functionality
    The installation process was simple, quick and effective
    Wow what a difference!
    I can now type in “real-time” rather that waiting for the Mac to catch up and can have more that one program open at a time
    Cannot praise enough – thank you for giving my my sanity back…

  25. Anonymous says:

     United Kingdom

    Perfect. Simple to fit on my new 2020 iMac and a fraction of the massively overpriced Apple upgrade. I now have 40gb of ram and the Mac is speedy as a speedy thing.

  26. Anonymous says:

     United Kingdom

    Purchased for my iMac 2020. You have to buy memory together, if they come with different batch, iMac may not reach the optimal speed for ram. so be mindful when upgrade.

  27. Anonymous says:

     United Kingdom

    I upgraded 2 laptops with this. one had 2 4gb 2666 sodim. The other 8gb, 2400 sodim. With this as the primary in one and the other 4gb – no windows test memory errors. With a 8gb 2400 primary in the other and 4gb 2666 in the other, no windows memory test errors. A bit lucky but fantastic. However, it does seem to play well with other manufacture

  28. Anonymous says:

     United Kingdom

    Purchased X2 16GB Modules To Add To My Mac Mini 2018 “The New Updates Model”. I Wasn’t sure if it would fit but it went in just fine and now my Mac runs a lot better.

    5.0 out of 5 stars Great RAM For The Money

  29. Anonymous says:

     United Kingdom

    Golden Review Award: 2 From Our UsersIt took me a long time to figure out which RAM I needed for my 2019 iMac 5K. I got in touch with Crucial through their website and this is the version which is designed for Mac. They said you can tell because the serial number ends in an M. (i.e. CT2K16G4S266M).

    Easy install and works great.

  30. Anonymous says:

     United Kingdom

    My 2017 5K iMac had 8GB of RAM it now has 16GB… Taking out the old RAM and replacing it with this kit (As opposed to simply adding it in) resulted in the Memory speed increasing to 2667Mhz which is a tidy little speed bump as well.

    Noticeably faster in some tasks, particularly memory intensive ones and gaming.

  31. RicardoEAQ says:

     United Kingdom

    Golden Review Award: 5 From Our UsersArrived with Prime fast, works perfectly as I used the Crucial UK website to identify the best modules to use and they provided a link to Amazon to buy the right ones.

    iMac 2019 27inch 5k Retina Model – existing base capacity 8GB; increased to 24GB.

    You can mix modules, you have to buy a kit or twin modules to fill in the two remaining slots.
    Gen. rule of thumb about RAM – buy in pairs and always fill in all available slots. 2 slots should remain free, never none or odd numbers i.e. 1/3.

    If you want to optimise you always put RAM with the highest capacity in the bottom (Bank 0) and 3rd (Bank 2) from the bottom. Then the original RAM modules swap to the new positions of slot 2 (Bank 1) and 4 (Bank 3).

    Where my pre-installed 2 NR 4GB modules were I swapped with the NEW 2 NR 8GB modules. And then put the already pre-installed 2 NR 4GB modules in the 2 remaining slots.

  32. Anonymous says:

     United Kingdom

    Golden Review Award: 2 From Our UsersReceived these promptly in the post but unfortunately they are too wide for the slots in the earlier iMac that I have.
    Called the support number 08000910021, chap was helpful and has promised to email me a list of compatible memory cards. Afraid this on has to go back.

  33. Anonymous says:

     United Kingdom

    Initially purchased parts recommended by Amazon which system did not recognise. Amazon issued refund
    Obtained above part No from Crucial. Make sure you buy this part.
    Used on late 2019, 27″ retina 5K iMac. Easy to instal. Recognised by system.
    8GB RAM expanded to 40GB; significantly cheaper than Apple upgrade.
    Works fine.

  34. QYAAlberta says:

     United Kingdom

    I’ve used Crucial for memory upgrades a number of times in the past. The chips are supplied in matched pairs as iMacs require. The installation on a 27″ iMac is a simple task and as soon as I was done with he install, I had 40G of memory to play with and my Photo and video editing got a lot quicker.

    The memory does what it says on the box and the price is excellent.

  35. SusannaDunrossi says:

     United Kingdom

    I bought these to upgrade the RAM on my iMac (2017) which came with the basic 16GB (2 x 8GB).
    The boards are easy to install (you have to be firm when pushing in the cards otherwise the iMac won’t restart).
    Apple charge considerably more for the same specification so I wholeheartedly recommend these.
    Remember to buy in pairs not singles.

  36. Anonymous says:

     United Kingdom

    Used as part of upgrading my 27in iMac from its base 8 GB up to 24 GB.

    I was a bit nervous about buying used memory, but the Mac was up and running smoothly within 10 minutes, and with a total cost of only 50, is significantly cheaper than the extortionate 360 (approx.) it would cost to get the equivalent configuration from Apple.

  37. Anonymous says:

     United Kingdom

    I purchased this to upgrade the RAM on a 2017 5K iMac 27″. I’ve used Crucial before on other Macs (MBP and Mini) and have always found the quality to be good for the price. Although the iMac 27″ has a hatch at the back of the screen to make RAM updates easy, it was a little trickier than I had expected to get the RAM recognized by Mac OS.

    My iMac came as standard with 8GB (2 x 4GB), so I put the RAM cards into the 2 empty slots. Upon starting, the iMac came on, but gave a permanent black screen. I then tried to reset the NVRAM/PRAM as others have explained, but this didn’t work. I took out the RAM cards and replaced again because some reviewers suggested it is hard to get a snug fit into the iMac RAM slots. I again performed a NVRAM/PRAM reset. I actually thought that this had failed again and whilst trying to find the Crucial Helpdesk number realized that the iMac flickered to life. As such, I think a degree of patience is required for the Mac OS to recognize the new RAM upon first installation…. Never had this problem with either my MBP or Mac Mini, but then again, these were straight replacements, whereas this was to install new memory into the 2 empty slots of the iMac. I’m very happy with the performance of the iMac now – 40GB should be more than enough for my current statistical analysis and computational modeling needs.

  38. Anonymous says:

     United Kingdom

    I had 16GB installed in my iMac 27 inch 2017 4.2Ghz i7, and then installed 32GB on top of that. I am lazy and keep 40 or so web pages open at any one time. I can switch between Word, Powerpoint and Safari and Firefox and rarely get system hangs. If they do happen, it is my fault for being lazy for not shutting down somethings when I have truly finished with them.

    Installation was fairly easy, but not a complete breeze. Read what others tell you about this.

    I am very happy and a lot less frustrated.

  39. Anonymous says:

     United Kingdom

    Golden Review Award: 3 From Our UsersBought these two 16GB for an iMac 27 inch Retina 5K, 3.4 GHz Quad-core Intel Core i5 supplied with 8GB RAM. The four RAM slots were occupied (from the top slot) were empty, 4GB module, empty, 4GB module. Added the two new 16GB modules in the empty slots and restarted the iMac. No dark screen or any other hitch just a normal start up but now with 40GB of RAM!

  40. Anonymous says:

     United Kingdom

    Always used crucial for my Mac memory in the past. This was for the 27″ iMac 5k 3.8GHz (2017 model). Added the 2 separately purchased 16GB sticks in slots 2 and 4 and the machine wouldn’t boot. After checking they were correct model and correctly seated I reset the PRAM/NVRAM using CMD+ALT+P+R when powering up and this resolved the issue. All boots fine and correctly reports my (40GB total) memory.

  41. XTGDonaldax says:

     United Kingdom

    So what could possibly go wrong when installing in an iMac 27″ – the black screen of course! Probably just me as usual. Anyway all good after a cup of tea and ginger biscuits. While turning on hold down keys ‘cmd’ and ‘option’ and ‘p’ and ‘r’ at the same time then release after a few seconds and breathe 🙂 Hope this helps.

  42. Anonymous says:

     United Kingdom

    Golden Review Award: 2 From Our UsersI bought the 32 GB (16 GB x 2 ) which was delivered very promptly the next day. Installation was a breeze, in fact about three minutes. I held my breath and switched on and after very brief initiation period of a minute she fired up at the speed of light and instantly showed that the capacity had gone from the preinstalled 8 GB up to 40 GB. When you consider the fact that the Apple memory is close to 750.00 and I paid 283.00? Bit of a no brainer really. Works perfectly and now a very happy bunny!!

  43. Anonymous says:

     United Kingdom

    Golden Review Award: 2 From Our UsersOne of the few things that Apple let you do yourself (and it’s easy). My recently purchased iMac came with 8gb RAM to upgrade with apple was several hundred pounds. buying two 8gb cards cost me less than 170 and took me all of three minutes to install, giving me 24 Gb RAM in total. They were accepted immediately by my computer and everything is working perfectly. With the Crucial guarantee there is peace of mind. I recommend this item as an Apple upgrade.

  44. GeorgiaPearsall says:

     United Kingdom

    Golden Review Award: 19 From Our UsersCrucial CT2C16G4S24AM 32 GB Kit (16 GB x 2) (DDR4, 2400 MT/s, PC4-19200, DR x8, SODIMM, 260-Pin) Memory for Mac

    My machine is a 27″ iMac 5K, mid-2017 model, 4.2GHz i7 processor and I was looking to upgrade on the original 8Gb memory. I was concerned that when one reviewer recorded that this memory hadn’t worked for them, I might suffer the same problem, though when I researched the Crucial website, the indication was that this part number should work.
    The original memory modules were inserted in locations 2 & 4 (counting “1” from the top of screen). When this (CT2C16G4S24AM) memory arrived, and I installed the modules in the empty 1 & 3 locations, I disappointedly found that the Mac wouldn’t boot up.
    After a call (0800 091 0021) to Crucial Technical Service, the very helpful agent confirmed that the part number should indeed work. I’m happy to say with a bit of perseverance, and great guidance from the agent, we found that by inserting the new modules in position 1 & 4, and the original modules in positions 2 & 3, my Mac booted up and found the full 40Gb.