MFM or ESDI QBUS controller for one PDP-11/23 PLUS

Understood. Most of the nonDEC FM/EDSI boards still require a distribution pannel as they were targeting DEC systems. At a minimum you need to make a hybrid cable to use them with one drive. How can you tell? Simple, if the board is said to do FM/EDSI and has only a 50pin connector a breakout board (distribution pannel) is required. Most do. I have several differnt examples of nonDEC MSCP controllers for floppy and hard disks and they all like the 50pin cable to breakout. There may be some that do not I don't have one. Actually there are several possible distribution or breakout boards. They primarily serve to translate the 50pin RQDX cable to the more typical cables used for floppy and FN/EDSI disks. One is the distribution pannel used in the BA23 and its only connectors and wires so easily duplicated. Its function is to take the 50pin cable from the RQDXn (or nonDEC MSCP) and route them to the 34pin connector for floppy and the 26/34 pin cables used for MFM. It is located in back of the drive bay of the BA23 and can be used outside of BA23. The second is the M9058 used in the BA123 and that is a dual width Qbus board that can support 1 floppy and 3 hard disks. It's Qbus but only takes power for running the local buffers and extended device select plus providing the interconnect point for the ready/writelock switch pannel. While it appears complex it's really trivial and is better described as a breakout board. If You get a M9058 it is not required to install it on the Qbus, only provide it with needed power if that is mechanically more suitable. The reason for that is while it's dual width it's thick due to the presence of many connectors. The M9058 is typically located outside the BA123 backplane cage nearest the disk bays for easy cable routing. There is a third board RQDXE that is for use mostly in BA23s for extending the RQDXn outside the case for additional drives. Its of limited utility as breakout/distribution. I know this from fitting two half height HD + RX33 in ba23 and also putting RQDX3 in BA11S with RX33 and 3 RD52s. Hope this helps. The only MSCP boards I've used that didn't require breakout were SCSI. Allison