At the bottom of this post if my iMac configuration. There is probably more information than you need, but I just copied and pasted from one of my previous posts. I'm thinking of upgrading my SSD. I'm read the Samsung 970 gets over 3gb/s for the M.2 SSD. I began researching and it appears that the iMac doesn't use an M.2, but more of a custom made SSD in that slot. First question is, is that true? I also read that there is a spot for a second drive (for when you order an iMac with HDD instead of SSD) and that I could put any normal SATA 3 SSD in there as a second drive. My second question is, is this true? Thanks everyone! iMac (Retina 5K, 27-inch, 2017) macOS High Sierra Version 10.13.3 4.2 GHz Intel Core i7 64 GB 2400 MHz DDR4 500 GB SSD Radeon Pro 580 8 GB External 3 USB3 slots with 27 card reader mounted under the iMac Displays (total of 3) 27-inch (5120 x 2880) (the iMac) Dual LG Ultra HD Display 27-inch (3840 x 2160) Storage Super Drive - I still haven't used it yet, but at least I have it. 500 GB Flash Storage (Macintosh HD) used for programs and stuff that stays on the iMac WD 8TB External HDD - used for every day storage such as pics, documents and stuff most people keep on their machines.. 1 TB External SSD (I forget exactly which one) - used for my work flow if all the footage is smaller than 1 TB 12 TB External HDD RAID 0 - used for my work flow if all material is over 1 TB; This runs pretty fast, but still nothing compared to SSD. Will upgrade to a large SSD RAID setup later this year. Backup I use BackBlaze. It backs up all of my iMac and 1 external (I have it backup my 8TB) Time Machine - I have a 4 TB WD My Passport I used for Time Machine because I also have an iMac at the office and 3 Macbook Pros, so I partitioned it and use Time Machine at least once a week on all machines.