[Info-vax] VAX 6000 on Young Sheldon

[Arne Vajhøj]

On 2/16/2023 9:47 PM, gah4 wrote:
> 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 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?

Sure.

And without /OVER=ID they will get an error.

With /OVER=ID then ...

Arne