OWC has taken apart the 27″ from 2020 and shows us the logicboard.
You can clearly see that the large 3.5″ hard disk is missing and leaves a lot of space behind. The new SSD is simply soldered onto the board, just like with MacBooks. So if the board fails, all data is lost. We can’t mention this enough and link here again to good backup programs as well as our guide for easy building your own cloud solution for backup.
Nevertheless there is a slot on the logicboard. This may be designed to accommodate more memory if you have ordered an iMac with 8TB SSD memory. If you can use this slot for later upgrades is not clear yet, but we will keep you informed.
What you can also see after the disk is removed: the internal components are getting smaller and smaller. Since this is the last iteration of an old design, we can assume that the successor iMac will be much slimmer and more elegant.