I remember the DPX/20 as being a rebadged version of an IBM RS/6000.
The ones I remember resembled this picture of an RS/6000, and ran AIX 3.2.5
I didn’t get that close to the various model numbers, I have half an idea that this was the 500 series of RS/6000.
In actual fact I was sent on my own driving to Central London with well over £200k’s worth of DPX/20 to install, being carried in the boot of a strange car only two days after passing my driving test!
I have memories of spending many hours experimenting and testing with writing backup scripts to make a MKSYSB Backup tape, and archive our own applications & systems on to it so that it could be taken to another machine and the machine “booted” from the tape in such a way that it would do a complete self restore. A very nice and neat idea that worked pretty well, assuming of course that you were using compatible hardware between the two systems.
These boxes also had some horrible Micro-9 pin connectors on expansion cards for Serial Terminal cabling. So much so that I was chopping up old cables to adapt them in to conventional 9-pin and 25-pin RS232 cables to Digital VT Series terminals. I also seem to remember these HAD to have fully wired and complex flow control wiring (especially for printers) as a result which was a real pain in the backside!