Early 3M Computer Tape Type Numbers

[Paul Koning]

> On Jun 26, 2020, at 1:46 PM, Tom Gardner <t.gardner at computer.org> wrote:
> 
> Paul
> 
> Thanks, I had found this ad a while ago but thought it was ¼-inch.  Upon careful reading all the notes I found, "Errors per roll based on recording 7 tracks on rolls ½" x 2500'. "
> 
> It looks like 3M may have called their computer tapes "Instrumentation" tape until the late 60s
> 
> Tom

"Instrumentation tape" sounds like a reference to instrumentation recorders, which were devices used to record N channels of analog data.  Typically this was done by FM-modulating that data for the actual recording process.  I've seen references to heads for such machines in widths from 1/4 inch to 2 inches depending on the number of channels needed.  I believe instrumentation tape was usually supplied on reels that look like professional audio tape reels -- metal flanged reels with hubs somewhat larger than a standard computer tape hub, with 3 small notches.

Some early computers used tape like that for data recording; for example, the Electrologica X1 used 1/2 inch instrumentation tape reels, recording data at 400 DPI (NRZI I think) in 10 (!) tracks.  Those were vaguely like DECtape -- random access rewritable blocks -- but with variable rather than fixed length blocks. 

Recovering data from such reels is an interesting problem today.

	paul