Partition Problems w/ 810mb HD

[cph@martigny.ai.mit.edu (Chris Hanson)]

   From: "Arturo J. Morales" <art@aaRS.mit.edu>
   Date: Tue, 26 Sep 1995 13:31:41 -0400

   I recently acquired an 810mb HD (IBM Brand) and proceeded to
   reformat and partition it so that I could have a DOS/Windows/OS2
   (FAT) partition and a Linux partition.  After formating the Drive,
   (using MS-DOS 6.22) I only saw 770 megs... I figured that it had
   defaulted to a huge sector size or something like that and
   therefore ignored the problem... Now I'm trying to use Linux's
   FDISK to create a linux and swap partition and it seems that my HD
   and the partition table are very confused.  Any sugestions? Should
   I reformat w/ PC-DOS? MS-DOS 6.3? Should I do a fdisk /mbr?

I went through this problem last week, with a Sigma Data drive.  The
Linux kernel (1.2.13) configured the drive geometry as 1571/16/63
(cylinders/heads/sectors) but DOS and OS/2 both configured it as
785/32/63.  Consequently Linux fdisk was unhappy with the partition
table that had been laid down by OS/2 fdisk.  If I had done the
partitioning with Linux, DOS and OS/2 would have been unhappy instead.

Since I don't know how to control the DOS and OS/2 geometry
configuration, I fixed the problem by forcing Linux to configure the
drive the same way that DOS and OS/2 do: using the following line in
my "/etc/lilo.conf" file:

	append="floppy=thinkpad hd=785,32,63"

BTW, this has nothing to do with formatting.  Only the partitioning
and the disk geometry matter, and if the systems all agree on the
geometry, then they will also agree on the partitioning.  So don't
reformat your DOS partition unless you have reason to believe that the
data on it is corrupt.

This also has nothing to do with 770 megabytes vs. 810 megabytes; the
disk has about 811x10^6 bytes, which is roughly 773x2^20 bytes.  It
all depends what you mean by a "megabyte" -- disk manufacturers tend
to use 10^6 bytes while fdisk uses 2^20.