Odd PDP-11 tape related question

From: Fred N. van Kempen <waltje_at_pdp11.nl>
Date: Tue Jan 13 14:25:34 2004

On Tue, 13 Jan 2004, Zane H. Healy wrote:

> The OS is RSTS/E and the tape is ANSI, at least I think it's ANSI and not DOS, I'd have to check to be positive. This much I do know, I've converted the TPC file to a SIMH TAP file, and read it without any problem under E11 and SIMH. I've even used E11 to convert it to a RSX TAP image, which I've written to 4mm DAT on the same drive, and I can't read it. I've also taken the TPC file and written it on VMS on the same model DAT drive.
>
> What really mystifies me is that I'm able to read the tape without any problem using E11 running RSTS/E. Yet, I can't read either DAT tape that I've made. I've been able to read other tapes made this way just fine.
Beware that *many* DDS1 drives cannot do variable-sized blocks very
well... if memory serves me right, RSTS BACKUP format uses many
block sizes in a single backup file:

80 - ANSI header
14 - RSTS file header
1024
2048\__ data block sizes, often +4
4096/
8192

This might be your problem.. even though the tape image is
fine, the drive doesnt let you use arbitrary block sizes.

This may or may not apply to your drive.. Nico might know
more about this- I just ran into this when writing an ASPI
layer for my software... I was unable to tell the DDS drive
to switch to 64-byte blocks.. it insisted on 512-b blocks.

Cheers,
        Fred
Received on Tue Jan 13 2004 - 14:25:34 GMT