Tape dumping programs for Unix/Linux...

From: Carl Lowenstein <cdl_at_proxima.ucsd.edu>
Date: Fri May 3 03:11:59 2002

> From: Raymond Moyers <rmoyers_at_nop.org>
> To: classiccmp_at_classiccmp.org
> Subject: Re: Tape dumping programs for Unix/Linux...
> Date: Thu, 2 May 2002 21:56:13 -0500
> In-Reply-To: <000501c1f245$6a304ca0$1aefffcc_at_Shadow>
>
> You really have me going about the 9 track behavior tho
> null portion of tape as record delimiters "crap in the gap"
> problems of the past, and other such things.
>
> So far what ive learned about those things is nothing as
> many years around this stuff conditioned me to expect.
>
> If i spool the whole raw tape using a driver that knows
> nothing of any null gaps and simply spool all bytes that
> are bytes to a file .... could not i then pull the desired content
> out of the spool if i knew the format of the data ?
>
> If random access is what they are doing, how did they deal
> with a rewritten record, pad the unused portion of the record
> to overwrite trailing garbage ? or was the bytecount in a rewritten
> headder so that the controller knew the valid byte count ?

By its physical nature, a magtape is a sequential-access device.
One can of course keep track of position on the tape and use it
as a "random-access" input device. Standard magtapes as block-replaceable
devices were not at all common, and were really sort of a stunt,
"see what I can do" phenomenon.

> a tape with blank as delimiter/filler and records with no or
> painfully terse descriptors seems to me very .... um something.

That's the way it is when hardware is not very clever. Back in
the olden days. However, the record mark delimiter was more sophisticated
than just blank tape. It was actually a pair of characters surrounded
by blank tape, a two-character record, that could be detected by
analog circuitry.

    carl
Received on Fri May 03 2002 - 03:11:59 BST