[Info-vax] VAX 6000 on Young Sheldon

[Jan-Erik Söderholm]

Den 2023-02-17 kl. 03:55, skrev 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
> 
> 

Note that you cannot mount using /ove=ide together with /system.
So you can use it locally for your own process, or just to lookup
the label and then dism and remount using the correct label.