Tarbell Cassette Interface and Protocols

[aminaas1573]

As a side note on our introductory tour, it would be possible to save multiple programs on these tapes, but you had to be very careful about where on the tape counter each program was placed, so your works didn’t override each other, an art far above the head of the impatient or unwilling to rewind to the beginning of the tape and carefully watch a rising counter number to find fresh fields of data.

And the result, not obvious otherwise, are these glyphs providing you a possibly cryptic map of “dumps” (writing of the programs into the tape, following the counter as you would go). Note how in the label, a failed/broken program has to be left where it is on the tape; a combination of hearing the old program under an overwritten phone number database one, as well as not being able to predict how many feet down the tape a new program will take, means the road to data dumps is littered with broken memories.



But what is exactly ending up on these audio cassettes (now considered to be data cassettes, or datasettes)?

Particularly curious folks can read up about examples like the here in the bitsavers collection. But in more general terms, a variety of standards (and not-so-standards) had emerged where pulses of sound went onto an audio cassette, and these sounds reflected individual data that could then be interpreted coming back off the tape. The distinction is important here – these were not digital signals, but digital information encoded as analog/audio recordings. Think of someone shouting the word “42!” instead of digitally encoding up-down on-off data like “101010”.