26 Dec
2005
26 Dec
'05
11:46 p.m.
Nico de Jong wrote:
From: "Miller, Keven" <kevenm at
reeltapetransfer.com>
Cc: <cctalk at classiccmp.org>
Sent: Saturday, December 24, 2005 12:25 PM
Subject: PDP-11 9-track tapes
>Recently I received 4 tapes from a PDP-11, RSX-11M, created
>with backup (BRU format), that I instantly get media read
>errors.
>Because of the "older" system, I am suspecting that they may
>
>
>be 800 bpi tapes.
>
>
very likely
I am not familiar with PDP, so I can only answer based on my experience.
7-track tapes went out of fashion around 1970 or so. In my first job I
encountered an IBM drive for 7 AND 9 track, and that was in 1969.
800 bpi would be more like it, but you didnt give the make/model of the
drive used, so that's only a guess.
I'd guess they were not 7 track. I think all of DEC's PDP11 drives were
9 track.
It could very well be a case of too large blocklength;
many drives (or
operating systems!) I've seen cannot read blocks larger then 32K. This is
especially a problem for tapes from the oil and geophysical industries.
The PDP11 is unlikely to have a block length more than 64K, as
that is the maximum memory available to be mapped at once.
With the need to have IO mapped to talk to the tape, I'd guess
it would have to be less than 24KW (48 KB), but some of that
memory would have to be used for the program (assuming no
I&D Space used). I'd guess >32K would be very hard to do.
If nobody else can be of help, you're welcome to
send me a tape, so I can
have a look at it
Cheers
Nico (located in Denmark)