Magnetic tape filesystem

Dave G4UGM dave.g4ugm at
Mon Feb 9 05:18:49 CST 2015

The Sinclair QL which was also sold as the ICL One Per Desk also had a serial tape type media  the ZX MicroDrive?


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Chuck
> Guzis
> Sent: 09 February 2015 08:37
> To: General at; Discussion at and Off-
> Topic Posts
> Subject: Re: Magnetic tape filesystem
> TI 99/4A initially presented the "wafertape" as an option (block-addressable-
> continuous loop).
> And, as mentioned, the stringy floppy, somewhat similar to the later
> wafertape and somewhat popular with the TRS-80 Model 1 crowd.
> The Coleco ADAM used a block-addressable tape, but I don't know what the
> read-after-write capability of the HE format tapes was.
> There's no reason that a 7- or 9-track tape could not be used as a random-
> access device, provided an adequate IRG was allowed for.
> Implementing read/write random-access filesystems on tape presents some
> significant issues.
> The first is the read-after-write physical block length problem, already
> discussed.
> The second is that extending files gets to be really interesting, unless file
> extensions get appended to the end-of-information point.
> The third is that it's pretty much impossible to deal gracefully with tape block
> flaws that develop some time after the block has been written.  In particular,
> the usual 9-track method of erasing over the bad spot and then writing a new
> block would create a problem by overwriting already-written data.
> Streamer drives are singularly awkward (although as I mentioned, one of the
> QIC vendors implemented a "virtual disk" system for the PC (Archive,
> Seagate...I don't recall).  Looking at the HP 35480 DDS OEM manual shows
> that the drive has to construct a new group from old data as well as new,
> write a temporary copy, then back up and attempt to rewrite the old data
> with the new.  Ugly stuff.
> --Chuck

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