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

[glen herrmannsfeldt]

Chris Scheers <chris at applied-synergy.com> wrote:
(snip)

> Actually, 9 track tapes have both logical and physical end of tape marks.
 
> The logical tape mark is written by software and can be any format as 
> appropriate for the label format.
 
> The physical tape mark is a reflective strip on the back side of the tape.
 
> After the physical tape mark, there is some writable tape.  Once the 
> drive indicates that the physical mark has been reached, it is expected 
> that the software will finish the current block and then write a logical 
> end of tape.  There should be enough writable tape left for that.

For reasonable blocksize, anyway.  There is a story of doing data
chainging on S/360, such that a tape can be written with one
very large block.
 
> Software that ignores this rule (either writing or reading) 
> can actually run the end of the tape off the reel.

Easy to do with a brand-new tape with no double tape mark EOF.
It will happen on label verification on IBM systems.
 
> This also happens when the end of tape sensor is inoperative.  <sigh>

-- glen