[Info-vax] TK50 - this is annoying...
Johnny Billquist
bqt at softjar.se
Tue Oct 9 15:51:54 EDT 2012
On 2012-10-09 20:30, Paul Sture wrote:
> In article <QMHlFQS6wZyr at eisner.encompasserve.org>,
> koehler at eisner.nospam.encompasserve.org (Bob Koehler) wrote:
>
>> In article <k4v41o$bte$1 at Iltempo.Update.UU.SE>, Johnny Billquist
>> <bqt at softjar.se> writes:
>>>
>>> Even by asking that question, you reveal that you have not used the
>>> TU58... :-)
>>> Slower than DECtape? Hell yes. DECtape flies compared to it. DEC did
>>> call the TU58 for DECtape II, but that really an abuse of the DECtape name.
>>
>> You got that backwards. I've done a standalone backup boot off TU58,
>> later followed by an OS upgrade.
>>
>> I've seen, but not used, DECtape. I had no idea how fast it actually
>> moved the small amount of data it held.
>
> I once met someone who had used DECtapes and he had been very impressed
> by them in their day, but he was at least 20 years my senior. IIRC he
> described some mechanism where they skipped alternate blocks when
> reading or writing so that the tape speed could be higher, and those
> skipped blocks were used when the tape was travelling in the opposite
> direction.
I still have DECtape, and occasionally use it. Not too bad. Although
having it as a system device for a PDP-8 is a lot slower than a disk.
But it's nowhere near as slow as a TU58.
If you have a acceptably fast system, you do not need to skip blocks,
but can keep it streaming at full speed.
It helps if you don't have an ass-stupid controller, such as the TD8E,
which actually don't do anything more than just pass each bit on from
the tape to the CPU. A TC01 will do DMA, as well as seeking without the
assistance of the CPU...
The TC11 was (as far as I remember, it's a long time since I touched
one), pretty good too.
Also, depending on the controller, reading backwards can become
interesting, since you might get bits inverted, and also reversed in
order in groups of 3...
> The Wiki entry unfortunately doesn't have any dates, but does claim that
> they were a lot more reliable than disks of the day:
>
> http://en.wikipedia.org/wiki/DECtape#Technical_details
>
> "Upon its introduction, DECtape was considered a major improvement over
> hand-loaded paper tapes, which could not be used to support swap files
> essential for practical timesharing.
DECtape is extremely reliable. A combination of recording everything
twice, as well as having a clocking track on the tape along with the
data tracks, not too high density, and also a physical construction that
protected the magnetic layer better. I have no problems reading DECtapes
that are over 30 years old now.
> The hard disk system (when it was working) was considered a "temporary"
> file storage device used for speed, not to be trusted to hold files for
> long-term storage. Computer users would keep their own personal work
> files on DECtapes, as well as software to be shared with others."
DECtapes are both extremely reliable, and are also, like floppies,
detachable. Do you could bring your own, with your files, and then take
it home with you afterwards.
>> I always suspected that DECtape is what the first initial in TECO
>> refers to. 8-)
>
> The official title of the TECO User's Guide says "Text Editor and
> Corrector", but it wouldn't be the first time an official version of an
> acronym differs from the unofficial original. ;-)
Right.
It was originally "Tape Editor and Corrector", and the tape referred to
is paper tape.
Johnny
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