command for mounting tapes

[HEDRICK at RUTGERS.ARPA]

From:  Charles Hedrick <HEDRICK at RUTGERS.ARPA>

Don't knock IBM systems in areas for which they are intended.  They may
not have EMACS, but IBM has put in more thought and had more experience
with data processing than the Unix world.  I don't know the context of
this comment, but if somebody is proposing a command to request the 
operator to mount a tape, most of the parameters mentioned are good ones:

  - vol_ser: Now and then people do make mistakes.  One of the major
	motivations for implementing labelled tape processing on Tops-20
	was so the system could automatically verify that the right
	tape had been mounted.  It is easy enough to mount the right
	tape on the wrong drive, or to get a couple of characters
	reversed and mount the wrong tape.  This can result in
	overwriting critical data.  Some of this is silly on a 4-user
	system that sits in the same room as the user terminals.  But on
	larger Unix timesharing systems, there are the same operational 
	requirements as for as IBM mainframe or a DEC-20.  My all means,
	tell the system what tape you want mounted, so it can check.
	The assumption is that vol_ser is a volume identifier that
	occurs in machine-readable form at the beginning of the tape
	in a tape level.  This switch should allow a list of volume
	identifiers, so that the system can switch automatically at
	the end of a reel.

  - file name: this seems a bit odd to me, but I didn't read the original
	proposal, so I don't know what it means.

  - mode: it sort of helps to tell the operator whether to put in
	a write ring

  - density: this may not be needed for read, but for writing, it is
	helpful to know at what density the user would like the label 
	written.

Of course these files (except for VOL_SER) should have default values.
In addition, Tops-20 has a couple of other useful options:

  - remark: a quoted string to identify the tape to a human, for sites
	that don't good enough tape management that the VOL_SER is
	enough.  /REMARK:"Look on the top shelf of cabinet 1"

  - protection: if you implement labelled tapes, specifies a byte
	that controls who can mount it.

  - label-type: if you mount a tape for writing, says what kind of
	label to write on it, in case the system supports more than
	one kind.  (Tops-20 supports vanilla ANSI, and a form called
	TOPS-20, which implements some extra fields that will be
	meaningful only to other Tops-20 sites.  We can also write
	EBCDIC labels, although we can't put any data on a tape
	labelled this way.  Well, it's easier to initialize tapes
	for our IBM system using the 20.)

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