16 Jun
2015
16 Jun
'15
5:54 p.m.
On Jun 16, 2015, at 3:48 PM, Eric Smith <spacewar
at gmail.com> wrote:
Johnny Billquist wrote:
DECtape has a timing track, but that can be written on site and simply runs the tape
takeup motor at its design speed, as far as I can tell. The reel dimensions of DECtape
ensure that the speed doesn?t change all that much (min : max diameter ratio is rather
modest).
paul
Then you can figure out tape speed across the
heads (if you care) by just observing flux changes.
Tony Duell wrote:
Only if there is something on the tape. These
computer tape drives could surely record on a
totally blank tape and get the right number of bits per inch. So the thing can't use
the data rate
at the head as a speed measurement.
Not for something that can write a blank tape (e.g. a 7-track or
9-track), but there were other tape systems that required a formatted
tape, and servoed the reel motors to the flux transition rate.
Obviously the factory had to use a drive with a different tape speed
control system to format the tape.