[Info-vax] TK50 - this is annoying...

[George Cornelius]

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 had heard that the data was written twice and always assumed (I
suppose correctly) that the extra blocks were for redundancy.  That
they might have been written in reverse bit order never occurred to
me.

I used them with Dibol on a PDP8/I and thought they were very slow
on write.  Then we got in the PS/8 (predecessor to OS/8?) O/S and
I found out otherwise.  Apparently DIBOL was writing with verify.

They were quite fast from my point of view at the time, and I
remember them being reliable.  At 200 bpi, with redundant writes,
on 1/2 inch reel-to-reel media, why not?

George