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+.\"	$NetBSD: fdisk.8,v 1.8 1995/03/18 14:55:34 cgd Exp $
+.\"
+.Dd April 4, 1993
+.Dt FDISK 8
+.\" .Os BSD 4
+.Sh NAME
+.Nm fdisk
+.Nd DOS partition maintenance program
+.Sh SYNOPSIS
+.Nm
+.Op Fl aiu
+.Op Ar device
+.Sh PROLOGUE
+In order for the BIOS to boot the kernel, certain conventions must be
+adhered to.
+Sector 0 of the disk must contain boot code, a partition table, and a
+magic number.
+BIOS partitions can be used to break the disk up into several pieces.
+The BIOS brings in sector 0, verifies the magic number, and begins
+executing the code at the first byte.
+This code is turn searches the DOS partition table for an `active'
+partition.
+If one is found, the boot block from that partition is loaded and replaces
+the original boot block.
+Under DOS, you could have one or more partitions with one active.
+The DOS
+.Nm
+program can be used to divide space on the disk into partitions and set
+one active.
+.Pp
+The NetBSD program
+.Nm
+serves a similar purpose to the DOS program.
+When called with no arguments, it prints the sector 0 partition table.
+An example follows:
+.Bd -literal
+	******* Working on device /dev/rwd0d *******
+	parameters extracted from in-core disklabel are:
+	cylinders=769 heads=15 sectors/track=33 (495 sectors/cylinder)
+
+	parameters to be used for BIOS calculations are:
+	cylinders=769 heads=15 sectors/track=33 (495 sectors/cylinder)
+		
+	Warning: BIOS sector numbering starts with sector 1
+	Information from DOS bootblock is:
+	The data for partition 0 is:
+	sysid 165 (NetBSD)
+    	    start 495, size 380160 (185 MB), flag 0
+		beg: cylinder    1, head   0, sector  1
+		end: cylinder  768, head  14, sector 33
+	The data for partition 1 is:
+	sysid 164 (unknown)
+    	    start 378180, size 2475 (1 MB), flag 0
+		beg: cylinder  764, head   0, sector  1
+		end: cylinder  768, head  14, sector 33
+	The data for partition 2 is:
+	<UNUSED>
+	The data for partition 3 is:
+	sysid 99 (ISC UNIX, other System V/386, GNU HURD or Mach)
+    	    start 380656, size 224234 (109 MB), flag 80
+		beg: cylinder  769, head   0, sector  2
+		end: cylinder  197, head  14, sector 33
+.Ed
+.Pp
+The disk is divided into three partitions that happen to fill the disk.
+The second partition overlaps the end of the first.
+(Used for debugging purposes)
+.Bl -tag -width "cyl, sector and head"
+.It Em "sysid"
+is used to label the partition.  NetBSD reserves the
+magic number 165 decimal (A5 in hex).
+.It Em "start and size"
+fields provide the start address
+and size of a partition in sectors.
+.It Em "flag 80"
+specifies that this is the active partition.
+.It Em "cyl, sector and head"
+fields are used to specify the beginning address
+and end address for the partition.
+.It Em "Note:"
+these numbers are calculated using BIOS's understanding of the disk geometry
+and saved in the bootblock.
+.El
+.Pp
+The flags
+.Fl i
+or
+.Fl u
+are used to indicate that the partition data is to be updated.
+The
+.Nm
+program will enter a conversational mode.
+This mode is designed not to change any data unless you explicitly tell it to;
+.Nm
+selects defaults for its questions to guarantee that behavior.
+.Pp
+It displays each partition and asks if you want to edit it.
+If you reply affirmatively,
+it will step through each field showing the old value
+and asking for a new one.
+When you are done with a partition,
+.Nm
+will display the information again and ask if it is correct.
+.Nm
+will then procede to the next entry.
+.Pp
+Getting the
+.Em cyl, sector,
+and
+.Em head
+fields correct is tricky.
+So by default,
+they will be calculated for you;
+you can specify them if you choose.
+.Pp
+After all the partitions are processed,
+you are given the option to change the
+.Em active
+partition.
+To change only the
+.Em active
+partition, you can use the
+.Fl a
+flag instead.
+.Pp
+Finally,
+when the all the data for the first sector has been accumulated,
+.Nm
+will ask if you really want to rewrite sector 0.
+Only if you reply affirmatively to this question will
+.Nm
+write anything to the disk.
+.Pp
+The difference between the
+.Fl u
+flag and
+.Fl i
+flag is that
+the
+.Fl u
+flag just edits the fields as they appear on the disk, while the
+.Fl i
+flag is used to `initialize' sector 0.
+The
+.Fl i
+flag instructs
+.Nm
+to start by making the first 3 partitions empty, setting the last partition
+to use the whole disk for NetBSD, and marking the last partition active.
+.Sh NOTES
+The automatic calculation of starting cylinder etc. uses
+a set of figures that represent what the BIOS thinks is the
+geometry of the drive.
+These figures are by default taken from the incore disklabel, but
+.Nm
+gives you an opportunity to change them.
+This allows the user to create a bootblock that can work with drives
+that use geometry translation under the BIOS.
+.Pp
+If you hand craft your disk layout,
+please make sure that the NetBSD partition starts on a cylinder boundary.
+(This restriction may be changed in the future.)
+.Pp
+Editing an existing partition is risky, and may cause you to
+lose all the data in that partition.
+.Pp
+You should run this program interactively once or twice to see how it works.
+This is completely safe as long as you answer the last question in the negative.
+.Sh SEE ALSO
+.Xr disklabel 8
+.Sh BUGS
+There are subtleties that the program detects that are not explained in
+this manual page.