dosd - MS-DOS file as a virtual disk

     The dosd* devices allow one to use an MS-DOS file  as  a  disk.   If  for
     instance the Boot Environment contains the setting:

          dosd0 = hd1:/minix/disk0

     Then the device /dev/dosd0 addresses all  the  blocks  in  the  DOS  file
     \minix\disk0  on  the  first partition of the Winchester hard disk.  This
     device may have one primary partition  table  to  create  the  partitions
     dosd1 through dosd4.

     One more virtual disk may be created by setting  the  dosd5  variable  to
     enable  the  devices  dosd[5-9].   The  MS-DOS  file  may  be  on any DOS
     partition on either a winchester or a SCSI disk.

     These devices allow one to run Minix within a DOS file, so  there  is  no
     need  to repartition the disk to make Minix partitions.  The Boot Monitor
     has an MS-DOS version that can boot Minix from a virtual disk.

     This driver has less then 20% performance overhead compared with  a  true
     partition due to the DOS file decoding.  Overhead can be minimized if I/O
     is aligned to DOS file clusters.  For  Minix  file  system  use  you  are
     advised to start the virtual partitions on even-numbered disk sectors, so
     that the  2-sector  Minix  blocks  do  not  span  clusters.   Minix  swap
     partitions  are  accessed  in units of the page size, i.e. 4096 bytes = 8
     sectors.  To minimize any overhead ever you could let partitions start on
     a  cluster  boundary.   The virtual disk will appear to have a track size
     equal to the cluster size, so a partition is cluster aligned if it starts
     on the first sector in a track.


     hd(4), sd(4).


     Philip Homburg (

  Manual Page
     Kees J. Bot (