>From: Chuck McManis <cmcmanis@mcmanis.com>

>I don't know of any tape that varies record lengths within a single _file_
>on the tape.
[...]
>If anyone has a counter example please let me know!

DOS-11 tapes for one (used by RSTS and of course DOS/BATCH itself).  The first
record of each file is a 14-byte label, all the other records are 512 bytes.
Then at the next tape mark it starts all over again.

RSX "BRU" tapes use all kinds of crazy record sizes all mixed together.
I just made a quick "test" tape image and the recls start out like this:

80 512 80 80 <TM> 80 512 512 80 512 80 80 4096 2560 80 4144 4144 4144 ...

ITS DUMP tapes (on the PDP-10) use all kinds of record sizes too, there's
a tape label at the beginning followed (w/o a tape mark) by the first file,
which has its own small label followed by the larger data blocks.

I forget what OS/360 labels look like?  I kinda remember them being
complicated...

In any case, even if the records between a given pair of tape marks are all
one size, dd is a pretty cumbersome way to copy labeled tapes.

John Wilson
D Bit