AVD - Assign Virtual Disk

  AVD is the task which assigns a virtual disk to a file,  and optionally
  creates  a new virtual  disk file prior to making the assignment.   AVD
  will also report  the file to which  a virtual  disk unit  is currently
  assigned.

  Several options are available for creating new virtual disk files.  The
  file size in blocks may be specified, or one of two default sizes (RK05
  or RX01)  may be used.   You may specify large file sizes (greater than
  65,536 blocks).   Also,  you may specify  the  placement  of the  file,
  giving the starting LBN.   This makes it possible to place VD: files at
  the far end of the disk,  preventing fragmentation  of your disk.   The
  starting LBN number may also be a large decimal number.

  Successful assignment  of a VD unit will bring the unit online,  as may
  be noted by a "DEV VD:" or "SHOW/DEVICE VD:".  Unassigned units will be
  marked "Offline".

  If the file access  fails,  the usual  cause  is that the file  was not
  deassigned prior to shutting down the system last time.   Note that AVD
  locks  the file,  and DVD unlocks  it.   If the  file  is locked  (do a
  directory  listing and look for the "L" in the line for the file),  you
  may unlock it with PIP using the /UN switch.

  For general  info on virtual  disks,  type HELP  VIRTUAL_DISKS  or HELP
  VD.  For information on deassigning virtual disks, type HELP DVD.

  The (MCR) command for assigning/creating virtual disk files is:

	AVD VDn:=file[/sw]

	VDn:	Virtual disk UNIT to assign. Range 0-7 at CSD.
  	file	FILE to be used as virtual disk. Defaults are SY0: for
		the device [0,1] for the UIC and ".DSK" for the file .
		type.
  	/sw	SWITCHES
  		/CR:n	Create file with "n" blocks (DECIMAL)
		/RX	Create file with 494. blocks (RX01)
		/DX	Create file with 494. blocks (RX01)
		/RK	Create file with 4800. blocks (RK05)
		/LI	List out file spec of this unit
		/ID	Report program version number
		/RO	Allow only read access
		/PL:n	Create file at logical block "n" (DECIMAL)

  NOTE: Virtual disks at are named after their volume label and kept in
        UIC [0,1]. For example, a volume labeled "RSXM32" would be kept
        in SY:[0,1]RSXM32.DSK.  It would then be sufficient to type "AVD
        VDn:=RSXM32" to assign the virtual disk.