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Thread: Multi-track cassette storage ever used?

  1. #1

    Default Multi-track cassette storage ever used?

    I was thinking about the 4 track cassette deck a friend of mine had back in the 1980's. He was into music and it let him mix his songs in his home studio. Instead of the normal dual section read/write head (for stereo) the head had four sections using both sets of tracks from the 'front' and 'back' of the tape.

    Doing a bit of research I found out that the big reel-to-reel tape systems on mainframe type computers used multiple tracks, for example the IBM System 360 was a 9 track, 8 data bits and 1 parity bit. I then got to wondering if any manufacturer had ever used a multi-track system for cassette (compact audio type cassettes) that were used on the 'home' computers back in the day. Using a 4 track head might have been much more costly as they were not really a commodity item but a stereo (two track) head would have been fairly inexpensive. You would have more required in the drives electronics but the mechanics would be the same.

    It seems it would have been a fairly easy way to increase the speed and/or reliability of cassette tape storage. In wondering how such a two track system might have been implemented the most obvious idea would be to read/write two bits at a time. But, you could also invert and or invert/delay the second track so that you have a crude way to detect errors or perhaps you could them read/write faster as the data would be redundant and you would not need as long a bit time?

    Anyhow, just thinking out loud and wondering what sort of multi-track tape systems there might have been other than for IBM sized machines.

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    Quote Originally Posted by Jeff_Birt View Post
    I was thinking about the 4 track cassette deck a friend of mine had back in the 1980's. He was into music and it let him mix his songs in his home studio. Instead of the normal dual section read/write head (for stereo) the head had four sections using both sets of tracks from the 'front' and 'back' of the tape.

    Doing a bit of research I found out that the big reel-to-reel tape systems on mainframe type computers used multiple tracks, for example the IBM System 360 was a 9 track, 8 data bits and 1 parity bit. I then got to wondering if any manufacturer had ever used a multi-track system for cassette (compact audio type cassettes) that were used on the 'home' computers back in the day. Using a 4 track head might have been much more costly as they were not really a commodity item but a stereo (two track) head would have been fairly inexpensive. You would have more required in the drives electronics but the mechanics would be the same.

    It seems it would have been a fairly easy way to increase the speed and/or reliability of cassette tape storage. In wondering how such a two track system might have been implemented the most obvious idea would be to read/write two bits at a time. But, you could also invert and or invert/delay the second track so that you have a crude way to detect errors or perhaps you could them read/write faster as the data would be redundant and you would not need as long a bit time?

    Anyhow, just thinking out loud and wondering what sort of multi-track tape systems there might have been other than for IBM sized machines.
    The only experience that I ever had with 'multi-track' sound was in my 1976 Olds Cutlass Supreme. I had an after market 8-track type cassette quad stereo system feeding 4 speakers, and it sounded pretty good. IIRC, quad tapes were hard to find back then. The one tape that most people like who rode with me, was the quad demo tape which had sounds like a bee flying around in the car. It was quite realistic. I knew some people who dabbled with quad home stereos in the early 80's but it was only a fad and soon passed into oblivion. On the other hand, I once worked in an area where we used inch 9 track tape for some data processing. Not much help here.

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    I've got a 3M QIC drive with a fixed head that uses 2 tracks--one for clock and one for data. I believe some early HP small systems such as the HP85 employed a similar scheme. For small media that's about as far as it went, I think. Most small multi-track systems employ bit-serial streams, like a floppy disk.

    There's a good reason for this--track skewing. The big 7- (you forgot those) 9-, 18-, 36-, 128-, 256- and 384-track drives are subject to tape "skew" issues, where bits in tracks do not arrive at the same time, either due to tape head construction or simple tape angular displacement or stretching. The circuitry to sort this out and the problem of producing a multi-track head with no skew make this strictly a course for the high-priced menu.

    On the other hand, the transfer speed is breathtaking.

    There were also disk drives that employed multiple-track head assemblies to speed transfer.

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    I think there were a couple of computers that used cassette designs with multiple tracks. I am blanking on the manufacturer that trumpeted using two tracks with identical information for data integrity. Might have been Wang but I am not sure. In cheaper systems, Coleco's DDP stored EOS data on one track while standard cassette bulk storage would be on the other. The biggest user of dual track cassettes was Atari but only one track had computer data while the other stored audio.

    The proposed precursor to the Sinclair Microdrive would have used 8-track as a base and recorded data on each track with an expected final capacity of about 1 MB. I don't recall if any of the shipped continuous loop tape drives used with computers had multiple tracks.

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    Are these multi-track systems still being used? There are ads from companies that
    repair these systems today...

    ziloo
    Last edited by ziloo; November 14th, 2017 at 10:39 AM.

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    Are there ary 3590s still being used? Probably. But they've been withdrawn from IBMs offerings since 2006. IBM stopped service about 2015. Although IBM called them "cartridges", I suspect the practical difference between a cassette and cartridge is one of scale.

  7. #7

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    This is all very interesting. Thanks.

    Now, my brain is wondering of any other storage schemes w.r.t. tape storage, i.e. rather than recording a tone or lack of tone to indicate a bit state was something closer to the modulation scheme used for modems tried?

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    Very few commercial tape drives used "tones" (PM or FSK). The recording method most commonly used is saturation recording, as found on disks. The actual encoding/modulation differs quite a bit among media types. Even in half-inch tape you have NRZI, PE and GCR modes. Even some of the systems that used what looks like audio cassettes used saturation recording.

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    There were a lot of different tape recording schemes plus "Turbo Loaders" that implemented forms of high speed compression on tapes. Just remember, for most of the home computer and PC market, reduced price was the prime driver with reliability coming in second and speed a distant third. That limited the extent of included features.

    Herb Johnson has a nice overview of the world of cassettes.
    http://www.retrotechnology.com/mcm800/mcm800_tape.html shows the differences between mono and stereo audio heads and the dual track streamer cassette head.
    http://www.retrotechnology.com/restore/cass_data.html covers a bunch more.

    Outside of those, the DEC TU60 and Coleco DDP are extensively documented high speed tape variations.

    Issue 3 of Ipso Facto, a Cosmac Elf related publication, includes an article that describes 8 early cassette recording techniques including the disadvantages of each. http://www.cosmacelf.com/publication...to-1-to-3.html
    Last edited by krebizfan; November 14th, 2017 at 10:52 AM.

  10. #10

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    The Atari 8-bit computer series had dual-track cassettes with program data in one channel and music and narration in the other channel, which the computer would play through the TV/monitor speaker:


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