I just read part of the Grant Saviers interview from CHM, where near the end he
gives a bit of history of DECtape. In particular, the fact that it was
derived from LINCtape though the format details are quite different.
A question popped into my mind, prompted by having read Guy Fedorkow's paper
about Whirlwind just a few days earlier: the Whirlwind tape format has 6
physical tracks but 3 logical tracks (each logical track is recorded
redundantly on two physical tracks) and one of those tracks is a clock track.
LINCtape and DECtape have the same redundant recording scheme, and also have a
clock track; the difference is that they add a mark track to enable the
recording of block numbers and in-place block writing.
That made me wonder if LINCtape was, in part, inspired by the Whirlwind tape
system, or if those analogies are just a concidence.
Incidentally, it's probably not widely known that LINCtape/DECtape is not the
only tape system with random block write capability. Another one that does
this is the Electrologica X1 tape system, which uses 1/2 inch 10 track tapes,
which include a clock and a mark track. An interesting wrinkle is that the X1
tape system lets you chose the block size when formatting the tape, and then
data block writes allow for the writing of any block size up to the formatted
block size. I'm not sure when that device was introduced; the documentation I
have is from 1964. There's no sign the designers knew of DECtape (or vice
versa).
paul
