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 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 at 23:18

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.

  • So... The answer is yes, they are still using proprietary connectors? No it is not a standard M.2 connector? – Wes Sayeed Sep 17 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. – Steve Chambers Sep 18 at 14:58

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