[Info-vax] Copying VMS SaveSet Under Windows

[Richard B. Gilbert]

On 11/21/2010 2:50 PM, Michael Kraemer wrote:
> JF Mezei schrieb:
>> About ANSI tapes:
>>
>> Question: does the tape drive itself signal end of file and end of tape
>> ? Or just end of tape ?

Both.  On reel to reel tape, there is a reflective marker shortly before 
the physical end of tape.  The tape drive senses this, ceases forward 
motion, and signals this to the program.  There are dozens of different 
types of cartridge tapes but all that I know of are able, somehow, to 
signal end-of-tape.

>>
>> or does the tape automatically skip inter block gaps and return block
>> after block, with only end of tape being signaled ?
>
> there's nothing magic about ANSI tapes.
>  From the tape drive's (and UNIX') point of view,
> the files on tape are still sacks of bytes,
> separated by single tape marks, and a double tape
> mark signals the EOT.
> It's just that some OS's (e.g. VMS) wraps
> each tape file in an extra header
> and an extra trailer file containing additional
> file info (name, date, recl etc), and the whole
> tape is assigned a volume label recorded somewhere
> in the first header. It's not rocket science,
> but of course requires some extra work to teach a Unix system
> to read that information - if anybody would be interested.

The basic problem with Unix is that it lacks the concept of "records". 
To Unix, the world is just a string of bytes.  Records are a figment of 
YOUR imagination and finding and interpreting them is YOUR problem.

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