------------------------------------------------------------------
      RX50 Diskette Driver for the IBM PC-AT
      ------------------------------------------------------------------
                                                         8 December 1984
      
      
      RX50DRVR.SYS is an MS-DOS loadable device driver which enables an 
      IBM PC-AT to read and write DEC RX50 diskettes on its high 
      capacity diskette drive.  To use the driver, copy it into the 
      root directory of your system disk and include the following line 
      in your CONFIG.SYS file:    DEVICE=RX50DRVR.SYS
      
      When the system is booted, the driver is loaded and it displays 
      its name, version number, load address and the drive letter to be 
      used to refer to RX50 diskettes.  This is normally D: but may be 
      different if you have a second hard disk drive or other block 
      devices installed.
      
      Once the driver is installed, all the normal disk commands can be 
      used EXCEPT the FORMAT command.  RX50 media cannot be formatted 
      by the IBM controller, and attempting to do so will make the RX50 
      diskette unusable.  Needless to say, references to drives A: and 
      D: should not be intermixed:  no good will come of it.
      
      The DOS direct disk read and write interrupts (25h and 26h) may 
      also be used.  Block numbers 0 through 19 are mapped to tracks 0 
      and 1 and the sectors are addressed in physical sequence.  Block 
      numbers 20 through 799 (which cover the area used by MS-DOS) are 
      mapped to tracks 2 through 79.  On each track the sectors are 
      interleaved 2:1 such that the logical sector sequence of 0..9 is 
      mapped to the physical sequence 1, 3, 5, 7, 9, 2, 4, 6, 8, 10.  
      This is consistent with the behaviour of MS-DOS on the DECmate 
      and the Rainbow.
      

      
      RX50INIT.COM is a program which initializes an RX50 for use with 
      MS-DOS.  It writes a FAT and directory in the format used by the 
      DECmate and Rainbow versions of MS-DOS.  The command format is:
      
             RX50INIT  [d:]  [volume-name]
      
      The drive letter d: is optional; D: is the default value.  The 
      volume name is optional; if it is omitted, no volume entry is 
      made in the directory.  If a volume name is given, it may contain 
      only letters, numerals, and hyphens.  Letters are converted to 
      upper case.

      NOTE:  After initializing a diskette, remove it from the drive and
      then reinsert it before using it.  This ensures that DOS recognizes
      it as a "new" diskette.

      
      RX50DRVR.SYS and RX50INIT.COM are copyrighted by Robert F. Morse. 
      Permission is granted for private non-commerical use only.  
      Questions, comments and suggestions may be sent to:
      
                     Robert F. Morse
                     17 Bowdoin Street
                     Cambridge, MA  02138
                     (617) 874-4250
  
                     DTN 223-6720
                     MLO5-2/B6
                     LEWS2::MORSE