[Info-vax] VAX 6000 on Young Sheldon

[Arne Vajhøj]

On 2/12/2023 6:52 PM, Johnny Billquist wrote:
> On 2023-02-12 01:28, Arne Vajhøj wrote:
>> On 2/11/2023 7:02 PM, Johnny Billquist wrote:
>>> On 2023-02-11 17:26, Arne Vajhøj wrote:
>>>> On 2/11/2023 11:18 AM, Tony Priborsky wrote:
>>>>> I'm pretty sure it didn't write a native VMS backup saveset -
>>>>> remember the CPU on the HSC was a PDP-11.   Logically the backup was
>>>>> the equivalent of VMS "BACKUP/PHYSICAL".  I seem to recall that at
>>>>> some point the VMS backup could restore (read) a HSC backup.
>>>>
>>>> So no CRC and no redundancy groups?
>>>
>>> Depends on how you mean that. Tapes have CRC on the data unless I 
>>> remember wrong. Just like disks have.
>>
>> As I remember 9 track tapes then it was pure data blocks
>> and tape marks - no CRC.
> 
> On a software level, you don't see this anymore than you see all the 
> extra cruft on a disk.
> 
>> If mounted as labeled tape then some blocks were
>> considered VOL and HDR blocks, but that was an OS
>> feature not a drive feature.
> 
> Correct. From a hardware point of view, those are just blocks just like 
> anything else. No difference at all.
> 
> However, the tape have blocks. You have the tape marks, blocking and 
> other stuff going on, to try to ensure your data is safe and don't get 
> corrupted. It's all down in the hardware, but that don't mean it work 
> any worse/different.

I guess I am too far distanced from the hardware.

To me a tapes content is what DUMP will show. I have
never wondered much about how blocks and bytes was
actually stored.

Links have already been posted to NRZI, PE, GCR etc. and
I can see that there are more differences than just 800, 1600
and 6250 BPI.

Arne