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Upgrading the BIOS with FreeDOS

You may want, or have a need, to update the BIOS of your PC, when the manufacturer of the motherboard announces some improvement of BIOS software. The installer program usually offered is an application to run MS-DOS.

This is a way to update BIOS from a USB-Device in linux. This will work with USB keys, USB-Sticks and with micro/mini/SD cards (with a suitable adapter).

Firstly, your BIOS needs to allow booting from USB - and be compatible with USB harddisks. Some BIOSes accept USB Floppies, CD-ROMs or ZIP drives, although these might be usable, it may be more difficult to implement the upgrade, however you may have no other choice, (netbooks in particular).

You need three things:

  1. A USB-Stick, preferably <2 GByte (FAT16 doesn't allow more than 2 GByte), and the base FreeDOS (fdbasecd.iso) install only uses 5.8 MByte. FAT16 is the recommended format as FAT32 is not detected as bootable by every BIOS.
  2. A FreeDOS install medium fdbasecd.iso (8MByte).
  3. qemu (apt-get install qemu), qemu is needed for the installer, basically the emulated qemu BIOS makes your USB-Stick appear to FreeDOS as an ordinary harddisk, so you can install as usual (and avoids burning the FreeDOS CD).
This is absolutly critical: at no stage is the USB-Stick to be mounted. Be very careful to select the correct device node, otherwise all data on the wrong disk will be erased without any redress, i.e. your main hard drive.

Plug in your USB-Stick, remember, don't mount it. Check dmesg (the last messages,if you just plugged it in), which device node got assigned to your USB-Stick lets assumes /dev/sdb .

Clear your USB-Stick,all data will be lost, you could also clear all of it, instead of just the first 16 MByte.

$ sux
dd if=/dev/zero of=/dev/sdb bs=1M count=16
16+0 records in
16+0 records out
16777216 bytes (17 MByte) copied, 2.35751 s, 7.1 MByte/s

Partitioning the USB-Stick

Partitioning and formatting your USB-Stick correctly is probably the hardest part.

Set the partition label to FAT16, on <2 GByte sticks (it offers better compatibility overall).

Next fdisk to partition:

# fdisk /dev/sdb
fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0xa8993739.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Now create a partition:

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
Partition number (1-4): 1
First cylinder (1-1018, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-1018, default 1018):
Using default value 1018

Confirm the creation of the partition by printing the partition table:

Command (m for help): p

Disk /dev/sdb: 2003 MByte, 2003828736 bytes
62 heads, 62 sectors/track, 1018 cylinders
Units = cylinders of 3844 * 512 = 1968128 bytes
Disk identifier: 0xa8993739

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1        1018     1956595+  83  Linux

Set the correct partition label, '6' for FAT16:

Command (m for help): t
Selected partition 1
Hex code (type L to list codes): l

 0  Empty           1e  Hidden W95 FAT1 80  Old Minix       be  Solaris boot
 1  FAT12           24  NEC DOS         81  Minix / old Lin bf  Solaris
 2  XENIX root      39  Plan 9          82  Linux swap / So c1  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  83  Linux           c4  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
 5  Extended        41  PPC PReP Boot   85  Linux extended  c7  Syrinx
 6  FAT16           42  SFS             86  NTFS volume set da  Non-FS data
 7  HPFS/NTFS       4d  QNX4.x          87  NTFS volume set db  CP/M / CTOS / .
 8  AIX             4e  QNX4.x 2nd part 88  Linux plaintext de  Dell Utility
 9  AIX bootable    4f  QNX4.x 3rd part 8e  Linux LVM       df  BootIt
 a  OS/2 Boot Manag 50  OnTrack DM      93  Amoeba          e1  DOS access
 b  W95 FAT32       51  OnTrack DM6 Aux 94  Amoeba BBT      e3  DOS R/O
 c  W95 FAT32 (LBA) 52  CP/M            9f  BSD/OS          e4  SpeedStor
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a0  IBM Thinkpad hi eb  BeOS fs
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a5  FreeBSD         ee  EFI GPT
10  OPUS            55  EZ-Drive        a6  OpenBSD         ef  EFI (FAT-12/16/
11  Hidden FAT12    56  Golden Bow      a7  NeXTSTEP        f0  Linux/PA-RISC b
12  Compaq diagnost 5c  Priam Edisk     a8  Darwin UFS      f1  SpeedStor
14  Hidden FAT16 <3 61  SpeedStor       a9  NetBSD          f4  SpeedStor
16  Hidden FAT16    63  GNU HURD or Sys ab  Darwin boot     f2  DOS secondary
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fd  Linux raid auto
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fe  LANstep
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid ff  BBT
1c  Hidden W95 FAT3 75  PC/IX

Hex code (type L to list codes): 6

Changed system type of partition 1 to 6 (FAT16)

Activate the new and only partition:

Command (m for help): a
Partition number (1-4): 1

Print out the new partition table again, reconfirm that the partition indeed got activated:

Command (m for help): p

Disk /dev/sdb: 2003 MByte, 2003828736 bytes
62 heads, 62 sectors/track, 1018 cylinders
Units = cylinders of 3844 * 512 = 1968128 bytes
Disk identifier: 0xa8993739

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1        1018     1956595+   6  FAT16

Write the new partition table to your USB-Stick and exit fdisk:

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: If you have created or modified any DOS 6.x
partitions, please see the fdisk manual page for additional
Syncing disks.
# exit

Format your newly created USB-Stick:

mkfs -t vfat -n FreeDOS /dev/sdb1

The preparatory phase is now complete.You have now partitioned and formatted the USB-Stick, there's nothing else left to do and you can directly go to the install process.

Booting up FreeDOS with qemu

As DOS has no idea of USB-Stick, you need to find a way to coax the FreeDOS installer into recognizing the USB as ordinary "harddisk", on live boot, the system's BIOS does that for us - but here the need to get inventive with qemu:

as user$:
qemu -hda /dev/sdb -cdrom /path/to/fdbasecd.iso -boot d

ctrl-alt will toggle mouse and keyboard grab and allow you to switch desktops to reread any instructions at each step.


This boots the FreeDOS CD and maps the USB-Stick raw device as primary master HD (here qemu's BIOS emulation abililty makes the USB-Stick appear to DOS as an ordinary hard disk). Select the installer from the start menu of the virtualised FreeDOS boot:

1) Continue to boot FreeDOS from CD-ROM

Keep choosing the default of 1 and/or choosing Yes when asked.


The install asks you to reboot - don't do that yet, as there is a need to fix up two errors in the FreeDOS installer for the mbr and bootmenu. Type the letter n.

freedos-do not reboot type n

Writing a bootsector to your USB-Stick

The first error to fix is the mbr with:

fdisk /mbr 1

The second error that needs fixing is the bootmenu in your new fdconfig.sys, run:

cd \
edit fdconfig.sys

and change the line starting to:

1234?SHELLHIGH=C:\FDOS\ C:\FDOS /D /P=C:\fdauto.bat /K set
(don't actually change this command, just add "1234?" to the begin of the line (before SHELLHIGH=C:\FDOS\ .....
NOTE it is to read : 1234?

Do not change anything else, as the line depends on your install setup.

Save it and exit "edit":


Once you're back to the command prompt, you can leave qemu.

Test to check if qemu will boot the USB-Stick.

qemu -hda /dev/sdb -boot c

Your USB-Stick is now bootable and contains a full FreeDOS install of 5.4 MByte, for flashing. You really should boot without any drivers (menu option 4), loading the himem.sys and emm386 files may otherwise interfere with your flashing programs!:

Updating the BIOS

Assuming your PC is up and running, plug in the FreeDOS USB-Stick, mount it and download the BIOS files needed, as recommended by the manufacturer of your motherboard/BIOS, to the FreeDOS USB-Stick, then umount the stick.

Power off your PC, plug in the FreeDOS USB-Stick, power up, so that you boot to the FreeDOS USB-Stick and follow the procedures of the manufacturer of your motherboard/BIOS.

Content last revised 08/01/2012 1800 UTC