Tape drive help and/or part needed (Attention DEC-heads!)

[Can't put tapes and disks on the same Massbus] Okay, I'm now officially confused by this whole Massbus thing. I'll explain how I thought it worked, and you all tell me where I'm wrong. The RH10 is a disk controller. It has one massbus coming out of it. Disks and tapes can plug into the Massbus - Just not both at the same time. I don't know why. In order to talk to the RH10, which is the massbus disk controller, you need a DF10 in front of it (Or were there other channel interfaces?). A DF10 is a small processor that knows how to read from the RH10 and write to memory. It's a DMA controller. (Can it talk to more than one thing at a time? Does it have it's own bus?) The massbus was 3 cables - 2 data cables and a control cable. They talk between the drives and had a decent bandwidth. All of the transfers on the massbus are either data moving between the controller and the drives, (Stuff from the registers on the drives), or data moving between the controller and the DF10. (Data being read from the disks.) The DF10 then plunks the data into memory and alerts the RH10 when it's done. The RH10 then PIs the processor (if enabled) and sets its DONE bit and such. -------