
                        DECUS VIRTUAL DISK PACKAGE

  The virtual disk system allows you to create a contiguous file and hook
  a device  driver  to it such that  the system  sees  a new disk  in its
  configuration.   The creation  and assignment  is done by the AVD task,
  deassignment is done by the DVD task.   The VD:  driver handles the I/O
  mapping from the device level to the file on the actual physical disk.

  You may do anything to a virtual disk that you can to a physical  disk,
  like running BAD on it, initializing it, running BRU on it unmounted or
  mounted, etc.

  To use the virtual disk facility,  you must first load the VD:  driver.
  To do this, you must say to MCR:

  	>LOA VD:/HIGH

  Next, assign (and optionally create) a virtual disk file.  See HELP CSD
  AVD for more info.   When  the assignment  is complete,  one of the VD:
  units will be online and the corresponding  file will be locked.   This
  binds a VD unit to a file.

  To deassign  a virtual  disk,  use the DVD task.  See HELP DVD for more
  information.

  The files are created with no extend or delete protection,  so you must
  change the file protection to delete a virtual disk file.

  Virtual   disk files are normally   kept in UFD [0,1]   and named after
  their volume label.  For example, a disk labeled "RSXM32" would be kept
  in SY:RSXM32.DSK.  See HELP AVD and HELP DVD for more information.

