> > On Nov 25, 2015, at 10:41 PM, Jerome H. Fine <jhfined...@compsys.to> wrote: > > >Johnny Billquist wrote: > …… > For example, the DSD 880/30 (from Data Systems Design of course) emulates > 3 RL02 disk drives using a single internal (non-removable) hard drive. The > box > also holds a single RX03 floppy disk drive (8" floppy disk drive which > supports > using single-sided media specified by DEC as an RX02 floppy in addition to > media which have the same physical interface, but which are double-sided). > For a Qbus system, the dual module controller was the interface to both the > three RL02 hard drives and the single RX03 floppy drive. I don't know if > DSD also made a separate controller for the Unibus for the DSD 880/30. > > With regard to the address support by the controller for the Qbus, the floppy > drive definitely supported only an 18-bit address. That 18-bit ONLY support > by DSD was identical to the 18-bit support that DEC provided for its Qbus > controller for the RX02, so both DEC and DSD needed a bounce buffer > managed by software to support the RX02 floppy disk for systems with more > than 256 KB of physical memory. > > As for DSD support for the RL02 for a 22-bit buffer address, a quick look > at the DSD manual was not able to say one way or the other. However, > it seems more likely the the DSD controller for the RL02 supported ONLY > an 18-bit address. I have all the DSD hardware, but it is not operational > at this point. If anyone else has experience with the DSD controller for > the emulated RL02, let us know if there was 22-bit address support for > its emulated RL02 drive. > > Jerome Fine
Confirming that the original DSD 880 only had support for 18 bits DMA. There are only 2 bits in the CS register for extended addressing. I doubled checked the RT-11 handlers I had. There was a Unibus controller for the original 7.8Mbyte RL02 reduced drive. Google 040018-01 DSD 880 Users Manual May81 The Sigma SDC RXV31 controller supported 22 bit DMA. See 400255-C SDC-RXV31 Floppy Ctrl Man Aug86 I used both, but double sided compatibility between the two products was occasionally spotty. Never did determine if it was a controller, floppy drive or media issue.
