.TH DOSD 4
.SH NAME
dosd \- MS-DOS file as a virtual disk
.SH DESCRIPTION
The
.B dosd*
devices allow one to use an MS-DOS file as a disk.  If for instance the
Boot Environment contains the setting:
.PP
.RS
.BR dosd0 " = " hd1:/minix/disk0
.RE
.PP
Then the device
.B /dev/dosd0
addresses all the blocks in the DOS file
.B \eminix\edisk0
on the first partition of the Winchester hard disk.  This device may have one
primary partition table to create the partitions
.B dosd1
through
.BR dosd4 .
.PP
One more virtual disk may be created by setting the
.B dosd5
variable to enable the devices
.BR dosd[5-9] .
The MS-DOS file may be on any DOS partition on either a winchester or
a SCSI disk.
.PP
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.
.PP
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.
.SH FILES
/dev/dosd[0\-9]
.SH "SEE ALSO"
.BR hd (4),
.BR sd (4).
.SH AUTHORS
.SS Software
Philip Homburg (philip@cs.vu.nl)
.SS "Manual Page"
Kees J. Bot (kjb@cs.vu.nl)