[Info-vax] VAX 6000 on Young Sheldon

[Arne Vajhøj]

On 2/17/2023 7:06 AM, Jan-Erik Söderholm wrote:
> 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 ...
> 
> 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.

And relevant for disks.

But I don't think I have ever tried /SYS with a tape.

Arne