Did you ever speak with anyone at System Source (Bob) about their PDP 12? Maybe they'd be interested in collaborating. http://museum.syssrc.com/
On Tue, Oct 13, 2015 at 10:54 AM, Paul Koning <paulkon...@comcast.net> wrote: > > > On Oct 12, 2015, at 9:16 PM, Rich Alderson > <ri...@livingcomputermuseum.org> wrote: > > > > ... > > The M tracks are longitudinally encoded (6-bit values chosen such that > they > > read the same as NRZ backwards and forwards for DECtape, 4-bit values for > > LINCtape) to predefine blocks (cf. disk sectors) for data. > > More precisely: it's Manchester encoding, not NRZ. The result is that > mark track codes are complemented and reversed end for end if you read them > in the opposite order. > > The code choices are such that this process (obverse complement) produces > another code word with the right meaning for this spot of the tape in that > direction. So "in the data field of the block" reads the same in both > directions. But "block start" in one direction reads as "block end" in the > other, which is just the result you want. > > The DECtape patent (3,387,293 -- on bitsavers among other places) > describes this very nicely. > > paul > > -- Bill