I will try with some of this. I am sure there is more in the list archives.
The MDS 800 was the first development system It was a Multibus 1 backplane
and usually had a CPU card, memory card, a two disk floppy drive controller, a
HD controller (SMD most likely) and a emulation card set. The dual 8 inch
disk drive unit you have is originally off one of these, that is why it is
labeled MDS 800.
The MDS 225 is either a System 2 or 3 in the development system line.
Usually the white ones were System 3s but not always. MDS 225 is the System 2 part
number. There is also a funny looking System 4 which uses 5 1/4 inch floppys
and HD.
In development work they usually were plugged into an ICE or In Circuit
Emulator. You have a ICE-51 which is used in developing circuits using the Intel
8051 or 8751 CPU chips. The ICE is usually plugged into the CPU socket in the
circuit it is emulating.
So they really are a computer system used for developing microcomputer
systems.
There is CPM available for the system 2 & 3s. They have been used for
writing documentation but this was not their main job.
Paxton
Astoria, OR