[Simh] Simh Digest, Vol 166, Issue 12

[Wilm Boerhout]

And it is DSC2, not VMS Backup that is used for the restore, since V1.x 
distros were in that format.

/Wilm

Johnny Billquist schreef op 6-11-2017 om 01:19:
> On 2017-11-06 00:39, Paul Koning wrote:
>>
>>
>>> On Nov 5, 2017, at 5:48 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>>
>>> Ah.
>>>
>>> That sound like a simh problem. The tape file itself have one of a 
>>> few different formats, none of them even keep any CRC (at least none 
>>> of the ones I can think of right now).
>>> The backing file storage just have the tape records. And obviously, 
>>> since the same backing file storage is used on both emulated tape 
>>> drives, there is obviously nothing wrong with the file.
>>>
>>> Any CRC indication is purely made up in simh. And that is where you 
>>> get the error indication. So I guess someone needs to dig into the 
>>> emulation of the Massbus tape drives.
>>
>> Another possibility: VMS BACKUP has its own CRC in its data blocks, 
>> entirely separate from the tape drive hardware check codes.  If 
>> BACKUP reports CRC errors, it's most likely talking about those.  
>> BACKUP also writes redundant blocks, so if only 1 out of N blocks is 
>> bad, the bad block can be reconstructed. Presumably, CRC errors 
>> reported by BACKUP are caused by flaws in the original material that 
>> was transcribed into SIMH tape images.
>
> ...in which case it should show up both using the TS11 and TE15. But 
> it only shows up in the TE16, which suggests that there is nothing 
> wrong with the contents of the actual tape image file.
>
> Correct me if I'm thinking wrong somewhere here.
>
>     Johnny
>