[rescue] Dumping SunOS tapes

Mouse mouse at Rodents-Montreal.ORG
Fri Sep 8 10:33:20 CDT 2017

>> Could you please show me a picture (pointer) of the cartridge + belt
>> you are talking about?

>> I do some 'vintage' tape deck restoration and have access to a few
>> belt suppliers....
>> If one knows the geometries of the belt, one can try to match it to
>> existing.

> I think you misunderstand where the belt is.

> The belt is actually inside the tape cartridge [...] [and,] unlike
> cassette deck belts etc, is very thin, [...]

True.  But see below.

> Each length of tape has varying sizes of belt as the belt runs around
> the tape spools themselves.

Yes.  It is not, strictly, the length of the tape that matters, but the
thickness of the tape-wound-on-the-reels (but the tape thickness is
standard enough that that varies with only the total tape length, in
practice); the belt runs around three (I think) idler wheels, around
approximately 1/4 of the circumference of each reel of tape, and, IIRC,
past a small cutout in the case where it can be pinched between a
driven roller and idler in the drive.  (I may be misremembering; the
belt could be driven entirely by the tape, with the roller and idler
pinching just the tape.  I don't have a cartridge handy to look at at
the moment.)  As tape winds from one reel to the other, the belt length
required for each reel changes, but the sum of the two stays very close
to constant.  (Maybe even as constant as the tape length; I'd have to
think about it more.  It's complicated by factors like the way the
fraction of the tape reel circumference covered by the belt changes
slightly as the reel fills and empties.)

It is, in a sense, a drive belt; it is part of the overall tape
transport, helping move the medium.  But there is one inside each
cartridge - they are not part of the "tape drive" device - and they are
not what belt suppliers are generally going to think of as drive belts.

All that said, if any belt supplier _can_ match them, I'm sure everyone
trying to recover data from QIC tapes would be delighted.

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