DGroves,
thanks for your reply. I do, however, wonder whether we are talking about the same motherboard. You are referring to an IDE port, but as far as I am aware of, the HP Z620 does not have any IDE ports - it is a SATA/SAS only system and actually lacks IDE connectors.
In terms of SATA DOMs, I do have a custome OEM SATA DOM sized at 1GB which is a left over from a NAS system which is no longer running with the original firmware but has rather been installed with FreeNAS using two USB sticks with 16GB each (mirrored). The SATA DOM I want to use uses a standard SATA connector as found on the motherboard, but requires power to operate and that is sourced through a floppy power connector, a so called "Berg connector" - see https://en.wikipedia.org/wiki/Berg_connector.
My SATA DOM looks similar to the right hand side one in your link from SuperMicro - although it is differently shaped and from a different company, but the connector is identical. It, however, only uses the 5V source from the floppy header (which also sources 12V) and therefore uses 2 pins of the 4 pin header only.
I was actually expecting to have the correponding header for that connector somewhere on the motherboard. So in essence, I am still searching for that header ...
The 1GB size is also plenty for what I want to use it for: The plan is to just use it to host the Clover bootloader in order to be able to install Windows 7 x64 on a HP Z Turbo Drive G2 which uses the NVME protocol not natively supported on the HP Z620. Clover would be able to circumvent that by starting a UEFI shell and then inserting an UEFI module to be able to access and boot from the NVMe SSD on the HP Z Turbo Drive G2
Regards, Atom2