DECassette questions

Ethan Dicks ethan.dicks at gmail.com
Thu Aug 25 15:30:47 CDT 2005


On Thu, 25 Aug 2005 16:16:44, Joe R. <rigdonj at cfl.rr.com> wrote:
>   I picked one of these up a while back and stumbled across it yesterday.
> It's a model TU80 IIRC.

Hmm... are you _sure_ about that?  The TU80 is a 42"-tall cab with a
flat mount (reels point at ceiling) 1600 bpi 9-track tape drive with a
pair of 50-pin formatted interface cables.  DEC made an interface for
it, and it's compatible with several 3rd-party interface boards
(Dilog, et al.)

Perhaps you have a TU60?  Audio cassette-sized cassettes, but with a
2mm notch in the middle of the top - data-grade only, not Radio Shack
cheapies.

> Does anyone have anyexperience with them? 

No.  I have one (with a Unibus interface), but I've never powered it up.

> I've
> never seen or heard of one in actual use but I know it's supposed to be
> useable on the PDP-8 so I may try to hand it on my -8 if they're any good
> (and I can find the right interface card).

You are looking for a TA8E card.  Not sure about the handle number.

> What kind of cassette tapes do
> they use and how hard are they to find and format?

What I have is an industry-standard data cassette - they look almost
exactly like home audio cassettes except for the 2mm notch in the top
middle of the case, and they typically have red or white plastic flaps
rather than bust-out-tabs for write protect - i.e. you can
write-enable a tape by flipping the flap over the hole again.

I suppose it would be somewhat easy to mod an ordinary cassette to
work in these, but I suspect that you might run into a long-term
reliability problem.  IIRC, the data cassettes used a thicker mylar
that would stand up to heavy use.  I certainly wouldn't bother modding
a C90 - we never used those for PET use back in the day - too thin and
fragile.  I'd start with a C20 or C30 and go from there, possibly as
high as a C60.

They aren't block structured as far as I know - more like traditional
magtape.  You should be able to boot from them, but I think in terms
of writing, you can only overwrite swaths of tape, not parts of files.

-ethan




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