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