On 11/20/2017 6:50 PM, Noel Chiappa via cctalk wrote:
> From: Charles Anthony> a hybrid PDP-11 (16 bits) / PDP-15 (18 bits) on a shared bus (UNIBUS?) That's a UNICHANNEL-15: it allowed devices on the -11 to do DMA directly into the PDP-15's memory through the MX15-B Memory Multiplexer. Odd factoid: this UNIBUS could run in 18-bit mode (!!), where the UNIBUS' two parity lines were recycled into 2 extra data lines. Some DMA interfaces (e.g. the RK11) could support this; in this particular case, it allowed the PDP-15 to use RK05 drives. Noel
More than just that - The DEC KS10 (PDP-10) used the UNIBUS and Massbus peripherals (RP06 disk, etc) in 18-bit mode. There was a special version of the RH11 (RH11C?) that had extra buffering and could be configured in "Fast Transfer Mode" where it used a pair of 18-bit UNIBUS transfers to do 36-bit DMA. I've never decided if this was really clever engineering, or just 'messed up' ... I guess it saved having 36-bit peripherals and peripheral buses. Rob.
