My old workhorse 17" MacBook Pro (circa 2011) finally gave up the ghost after 8 years of reliable service (may it rest in peace), and I'm looking into a 27" iMac to replace it.

I want to buy the high-end model iMac with the fusion drive and make the following upgrades:

  • Replace the 128GB SSD with a 1 or 2TB SSD.
  • Replace the 3TB spinning HDD with the largest SATA drive that will physically fit inside the case (hopefully a 12 or 16TB drive - I need lots of storage).
  • Ditch the Fusion Drive setup in favor of two independently formatted internal drives.

I understand that this is complicated surgery for this model and I have the skills necessary to perform the work. But since my previous machine is so old, I am a bit out of the loop on newer Apple hardware. I know that Apple was using proprietary connectors for their SSDs a few years ago (they were first to market with PCIe-based SSDs before the NVMe spec was finalized in the PC world).

So my question is, does the onboard PCIe SSD connector on the 2019 27" model conform to one of the industry standard M.2 form factors, or does Apple still use their own proprietary blade-style SSD connectors?

Also as a bonus, what is the maximum height clearance for the 3.5" SATA hard drive bay?

  • I’m a big fan of getting the CTO ssd you know you need for 2 years and then bumping storage. The thunderbolt 3 adapter to dual M.2 cases are so price attractive you can off board whatever storage your heart desires. @ me if you want an answer with part suggestions. We 256 most iMacs now at work with only a few 512
    – bmike
    Sep 17, 2019 at 23:18
  • Firstly, I'd avoid the Fusion drive. I had one when they first came out in 2012, and it got slower and slower as the drive filled. I eventually replaced the SSD portion with a larger SSD, and left the HDD as a spare disk. Secondly: I'd get the 256gb SSD to boot an OS and provide some storage, and then use external storage for additional files.
    – benwiggy
    Mar 2, 2020 at 21:38
  • @benwiggy; I only ordered the Fusion Drive model to make sure I had all the connections I needed to do the upgrade I wanted. Apple has a habit of deliberately frustrating attempts to do “unauthorized” upgrades. As it now sits, I have two independent drives, not a blended Fusion Drive.
    – Wes Sayeed
    Mar 2, 2020 at 21:52
  • @WesSayeed Excellent! However, I'd suggest that Apple designs its computers with no thought to user modification, rather than anything more sinister. They do what's best for making the device as they want it.
    – benwiggy
    Mar 3, 2020 at 7:31

2 Answers 2


These models support a 7 mm tall SATA III (6 Gb/s) hard drive for the primary storage (using the 3.5" size as opposed to the 2.5"), and getting the Fusion drive means you'll also get what's called a small "blade" SSD via a PCIe connector. Without this you can't attempt what you're wanting to do.

So, in summary:

  • Primary storage uses a 3.5" 6 Gb/s SATA 3.0 connection
  • Secondary storage uses a NVMe PCIe "Blade" connection

However, getting a compatible "Blade" SSD is not as easy as walking into any computer store and buying one. You will need to purchase one from a vendor that specialises in Mac hardware to ensure you get what you need.

I haven't actually seen inside a 2019 model 27" iMac yet, so can't give you a definitive answer in terms of height clearance.


Before biting the bullet and ordering one of these machines, I would take a look at the following to ensure you can get what you need and also do what you want.

Since you have the skills necessary to perform this upgrade, I would focus on ensuring you can actually get a compatible SSD with the storage you need.


  1. For something like this I also recommend contacting OWC to discuss your requirements.
  2. There would be no need for you to get the 3TB capacity Fusion drive in order to be able to do this, unless you want that capacity for whatever you intend to do with it later.

Disclaimer: I have no affiliation whatsoever with OWC.

  • 1
    So... The answer is yes, they are still using proprietary connectors? No it is not a standard M.2 connector?
    – Wes Sayeed
    Sep 17, 2019 at 22:47
  • Check out ifixit.com. They often have the info you need on hardware specifics, perhaps they will have the info you need. Sep 18, 2019 at 14:58

Yes, Apple is still using proprietary SSD connectors as of 2019.

I purchased the 27-inch 2019 iMac with the Fusion Drive option and it contains the following for internal storage connections on the logic board:

  • 1x proprietary Apple SSD "blade" connector.
  • 1x proprietary SATA power connector.
  • 1x industry standard SATA III data connector.

To upgrade the SSD:
I needed to purchase an adapter to connect the 2TB Samsung EVO Plus I ordered. The adapter I received had no electronics on the board whatsoever, so apparently Apple's proprietary connector is just a standard NVMe connector with different pin layout (although it might have other functions in other models).

NOTE: The SSD connector's position on the logic board only gives 5mm of clearance with the iMac's tapered aluminum body! If you're going to use a heat sink on your SSD (which is highly recommended for the SSD I bought -- it runs HOT), you MUST use a low-profile heat sink. The first one I ordered was 7mm tall and it didn't fit.

To upgrade the HDD:
I was able to use an ordinary 3.5" 16TB SATA III desktop hard drive without issues. The drive bay is nearer to the center of the iMac's body so it has much more clearance. The drive I ordered was 12mm high (which is pretty thick), but it fit just fine with room to spare.

NOTE: Even though the SATA data header on the logic board is standard, the power header is not. Connecting a standard SATA drive requires the use of a proprietary cable for getting power to it. The Fusion Drive models obviously include the cable, but I don't know if non-Fusion Drive models come with one.

I am happy to report that after putting everything back together, it runs like a champ. I've put this machine through some stress testing over the past couple months and have encountered no issues whatsoever. Fans run at normal speeds, and the SSD temps barely go above 50°C.

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