/tape_io directory                                       December 1994

The procedures in this directory fall into two classes:

    (1) Unix procedures that emulate the intrinsic VMS IDL tape manipulation
        commands (e.g. TAPRD, TAPWRT).    These procedures were written by
        Bill Thompson for the SERTS (Solar EUV Rocket Telescope & Spectrograph)
        and are detailed below.
    (2) Procedures that use the VMS IDL tape commands to read, write and
        manipulate a FITS tape.   By using the the procedures of class (1),
        these FITS tape procedures can also be used on Unix machines



			 CDS/SERTS Unix Tape Utilities

The procedures in this directory are intended to emulate in Unix the intrinsic
tape routines available in the VMS version of IDL.  The following routines are
available:

	REWIND		Rewinds the tape
	SKIPF		Skips files or records
	TAPRD		Reads tape blocks
	TAPWRT		Writes tape blocks
	WEOF		Writes an End-of-file mark

In addition, there is the routine CHECK_TAPE_DRV which is an internal routine
used by the other routines.

Also, the routine DISMOUNT emulates the Unix command of that name.  Although
this is not a standard IDL function, it is available as separate LINKIMAGE
software for VMS.  The Unix equivalent closes the file unit open on the tape
drive, and optionally unloads the tape.  Errors can result if the tape is
unloaded manually instead of using DISMOUNT.

These procedures are intended to emulate their VMS equivalents as closely as
possible, so that software can be written which is portable between VMS and
Unix platforms.  Towards that end, it was decided to reference tape drives by
number as is done in VMS.

In VMS, the tape drive numbers 0-9 translate into names "MT0", "MT1", etc.
These can be associated with actual tape drives through the use of logical
names, e.g.

	$ DEFINE MT0 $1$MUA0

In Unix, with this software, the same thing is done, except that environment
variables are used in place of logical names, e.g.

	> setenv MT0 /dev/nrst0

As always in Unix, case is important.  Thus, if the above environment variable
is set, then when the software refers to tape 0, the tape drive /dev/nrst0 is
used.