[Simh] SIMH tape images to real tapes

[Rich Alderson]

> Date: Sat, 17 May 2014 18:26:33 +0200
> From: Johnny Billquist <bqt at softjar.se>

> On 2014-05-15 23:10, Clem Cole wrote:

>> In 9-track world, the end of each file is mark as a single meta record
>> (tape mark),  Two in the row marks end-of-tape.   So the when you write
>> a take the driver check to see if its at start of tape and if not, has
>> to backs up over the last tape mark and then start writing.  On close it
>> writes 2 tape marks.

> The two tape marks for logical EOT is a convention, and not all software 
> adhere to it. But in general, right. I think someone else mentioned it, 
> but it's worth pointing out that for ANSI labelled tapes, the tape marks 
> are not used this way, for example.

Actually, tape marks are used in just this way on ANSI and IBM/EBCDIC tapes.
The "headers" and "trailers" of labeled tapes are physically separate files,
with the physical demarcation of tape marks and interfile gaps and all that
telling the OS where to find them.

Now CDC 6000 series tapes don't adhere to this convention, but that's an
entirely different drum of worms.

                                                                Rich