PAGE 225 The Custom TRS-80
Interesting! I see the experimenter uses the convenient but unusual choice of DTMF for recording, and is reduced to a very low symbol rate to get useful reliability. (Even though it seems that the tape speed is twice that of compact cassette.)
I note the article is about the 8-track cartridge format, rather popular at one time in the US but less so elsewhere, an endless loop format. (It just happens that I saw actual 8 track tape - in reel to reel format - at the recent vintage audio fair. Those devices were priced at ÂŁ650, presumably built for studio use, allowing independent recording and playback on each of 8 tracks. 8 VU meters!)
(Here’s a couple of videos of 8 track reel to reel decks: half inch, and quarter inch - not sure if either are what I saw at the weekend.)
From the linked TRS-80 compendium (thanks - also available paginated and OCRd here and here), I see the suggestion is to perform surgery on an 8-track cartridge to reduce it to a two-minute loop (from 280 down to 40 feet of tape) for access time convenience (there being no rewind facility!)
The article mentions the commercially made but utterly unsuccessful Compucolor 8001, with dual 8-track cartridge for storage. It uses 8 mono tracks, which seems quite sensible. The majority Compact Cassette storage uses them as 2-sided mono whereas they are capable of 2-sided stereo.
This page has good technical info on the history of compact magnetic media.
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So, a big, slow Sinclair Microdrive, then?
Using DTMF was certainly a mood. Even MOS/Commodore’s “let’s store binary as ASCII hex digits on tape at 300 baud - twice!” seems like a better option. MOS’s excuse was that it was the same way that hex was stored on paper tape. Commodore’s excuse was that they were very, very cheap indeed and change costs money.
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As a sidenote, the Exidy Sorcerer (1978) used just the shells for its ROM PACs. Some attribute this as the first cartridges for a commercial home computer.
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Some years ago, I ran across a posting on another forum that mentioned use of Muntz four-track tapes for data storage. These were derived from the Fidelipac system used for advertisements and PSAs on radio stations from the late 1950s until very recently, and of course the Muntz auto stereo system lost out in the market to Lear’s 8-track juggernaut.
The Fidelipac system featured tape speeds up to 7.5 ips with 30 ips fast-forward, so it might actually have been a good alternative in 1975-77. Recording electronics might have been derived from the excellent Datapoint tape system that used Philips cassettes with data-grade tape running at 7.5 ips. Imagine one of those puppies attached to a 16k RAM TRS-80 Level II. All RAM could have been loaded or dumped onto 17 inches of tape in about 25 seconds. Speedy!
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I suspect one could still build a good cassette interface, but you can’t get the media anymore.