DECtape ancestry

[Bill Degnan]

Paul,
Very interesting, thanks for sharing.
Bill

On Thu, Mar 11, 2021 at 7:54 PM Paul Koning via cctalk <
cctalk at classiccmp.org> wrote:

> 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
>
>