[Info-vax] 9 track end of tape (Was: Copying VMS SaveSet Under Windows)

[glen herrmannsfeldt]

Alan Frisbie <Usenet02_REMOVE at flying-disk.com> wrote:
(snip)

> The other odd tapes we had to deal with had to be processed in
> reverse order -- last record first.   The program would skip to
> end-of-file, then enter a loop of backspace-backspace-read,
> backspace-backspace-read, backspace-backspace-read...
> The noise from the tape drive was frightening, and we were shortly
> asked to refrain from running it on the S/360.

The usual S/360 tape drives have a "Read Backwards" channel
command that will read the block while moving the tape backwards.
The program supplies the address of the end of the buffer,
and the drive fills the buffer from the end toward the beginning,
such that the data ends up in the right order.  There are sort
algorithms optimized for "Read Backwards" to avoid the rewind time.

Not so long ago, someone had TOS/360 running on the Hercules 
S/360 emulator.  To get it to run, the "Read Backwards" command
had to be added to the emulated tape.

-- glen