[Info-vax] VAX 6000 on Young Sheldon

[gah4]

On Thursday, February 16, 2023 at 5:59:57 PM UTC-8, Arne Vajhøj wrote:
> On 2/16/2023 2:52 PM, gah4 wrote: 
> > The first thing OS/360 and successors do when a tape is mounted, 
> > is read the label (,SL), or verify that there isn't one (,NL). 
> > Systems I knew would let you read, but not write, with (,BLP). 
> > (That is, bypass label processing.)

> MOUNT /OVER=ID on VMS bypasses everything.
> > The drives will read until they find either data or a tape mark, or the 
> > tape goes off the reel. (The foil EOT markers are only used on writing.) 
 
The idea of labels, is that it protects against the operator mounting
the wrong tape.  If you say (,NL) then it verifies that there isn't a label.

I used to know a program that would tell you, at a low level, what
was on a tape.  I believe it would even read past the double tape mark
that is supposed to end the tape.  And for that, you mount (,BLP)
but also have to have the write ring out.  The OS verifies that.

Among others, it tells you the data set names on the label,
so you can read them if you forget them.  

There might be systems that allow (,BLP) for writing, but not
the ones I used.  

Do VMS operators ever mount the wrong tape?