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7. Accessing Huge Disks When the BIOS Can't

Notice: 1GB is "Huge"? Well, once upon a time...

The system in my office has a 1GB IDE drive. The BIOS can only see the first 504 MB of the IDE. (Where MB means 2**10 bytes, not 10**6 bytes.) So I have MS-DOS on a 350 MB partition /dev/hda1 and my Linux root on a 120 MB partition /dev/hda2.

MS-DOS was unable to install itself correctly when the drive was fresh. Novell DOS 7 had the same problem. Luckily for me, "Options by IBM" forgot to put the "OnTrack" diskette in the box with the drive. The drive was supposed to come with a product called "OnTrack Disk Manager." If you only have MSDOS, I guess you have to use it.

So I made a partition table with Linux' fdisk. MSDOS-6.2 refused to install itself in /dev/hda1. It said something like ``this release of MS-DOS is for new installations. Your computer already has MS-DOS so you need to get an upgrade release from your dealer.'' Actually, the disk was brand new.

What a crock! So I ran Linux' fdisk again and deleted partition 1 from the table. This satisfied MS-DOS 6.2 which proceeded to create the exact same partition 1 I had just deleted and installed itself. MS-DOS 6.2 wrote its Master Boot Record on the drive, but it couldn't boot.

Luckily I had a Slackware kernel on floppy (made by the Slackware installation program "setup"), so I booted Linux and wrote Lilo over MS-DOS' broken MBR. This works. Here is the /etc/lilo.conf file I used:

boot = /dev/hda
map = /lilo-map
delay = 100
ramdisk = 0             # Turns off ramdisk in Slackware kernel
timeout = 100
disk = /dev/hda         # BIOS only sees first 500 MB.
   bios = 0x80          # specifies the first IDE.
   sectors = 63         # get the numbers from your drive's docs.
   heads = 16
   cylinders = 2100
image = /vmlinuz
  append = "hd=2100,16,63"
  root = /dev/hda2
  label = linux
  vga = extended
other = /dev/hda1
  label = msdos
  table = /dev/hda
  loader = /boot/chain.b

After I installed these systems, I verified that the partition containing the zImage, boot.b, map, chain.b, and message files can use an msdos file system, as long as it is not "stackered" or "doublespaced." So I could have made the DOS partition on /dev/hda1 500 MB.

I have also learned that "OnTrack" would have written a partition table starting a few dozen bytes into the drive, instead of at the beginning, and it is possible to hack the Linux IDE driver to work around this problem. But installing would have been impossible with the precompiled Slackware kernel. Eventually, IBM sent me an "OnTrack" diskette. I called OnTrack's technical support. They told me Linux is broken because Linux doesn't use BIOS. I gave their diskette away.

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