[Info-vax] 9 track end of tape (Was: Copying VMS SaveSet Under Windows)

[Chris Scheers]

Bob Koehler wrote:
> In article <4ce97016$0$2290$c3e8da3$c8b7d2e6 at news.astraweb.com>, JF Mezei <jfmezei.spamnot at vaxination.ca> writes:
>> About ANSI tapes:
>>
>> Question: does the tape drive itself signal end of file and end of tape
>> ? Or just end of tape ?
>>
>> or does the tape automatically  skip inter block gaps and return block
>> after block, with only end of tape being signaled ?
> 
>    It no doubt depends on the tape technology.  Old 9-tracks had a 
>    special block that was written to the tape and indicated end of 
>    file.  Generally the controller/formatter would recognize this and 
>    pass and EOF indication back, not data.  IIRC on 8mm this had to be 
>    emulated.

Actually, 9 track tapes have both logical and physical end of tape marks.

The logical tape mark is written by software and can be any format as 
appropriate for the label format.

The physical tape mark is a reflective strip on the back side of the tape.

After the physical tape mark, there is some writable tape.  Once the 
drive indicates that the physical mark has been reached, it is expected 
that the software will finish the current block and then write a logical 
end of tape.  There should be enough writable tape left for that.

Software that ignores this rule (either writing or reading) can actually 
run the end of the tape off the reel.

This also happens when the end of tape sensor is inoperative.  <sigh>

-- 
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Chris Scheers, Applied Synergy, Inc.

Voice: 817-237-3360            Internet: chris at applied-synergy.com
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