Magnetic tape filesystem

Eric Smith spacewar at
Mon Feb 9 02:09:08 CST 2015

I wrote:
>> Some members of the 6502 Group (established 1975, still meeting
>> weekly) developed the XPL0 programming language (similar to ALGOL and
>> BCPL), and an operating system partially written in XPL0, called TFS
>> ("Tape File System") for use on homebrew or Digital Group 6502-based
>> systems with digital cassette drives.  TFS eventually evolved into FFS
>> ("Floppy File System"), and then APEX, which was sold for use on the
>> Apple II by Apparat (better known for NewDOS/80).

Tom Sparks <tom_a_sparks at> wrote:
> I think I found what you are talking about at

Actually not.  While some 6502 Group members did use Digital Group
6502 systems, the majority of the FFS work was done with surplus
digital tape drives with bit-banged manchester encoding, not with
Phideck transports or the Digital Group GCR controller.

I've never heard of anyone writing a 6502 or 6800 operating system for
the Digital Group Phideck subsystem.  There was Phimon for the 8080,
which of course would also run on the Z80.

I was in junior high at the time, and couldn't afford a computer of my
own of any sort, though I drooled over the Digital Group brochures. In
the late 1990s I purchased a used Digital Group Z80 system with a
Phideck subsystem, and a 6502 Group member gave me his Digital Group
6501 (not 6502!) CPU card.  (It was the Digital Group 6800 CPU card
with a MCS6501 installed; I don't know whether the Digital Group
originally sold it that way, or whether my friend replaced the CPU
chip and reprogrammed the 1702 monitor EPROM.)  It might be
interesting to try to get Apex to use the Phideck subsystem, but in
general I have better or at least more interesting things to do in my
"copious free time".

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