Dual boot ELKS and DOS

ELKS has a built-in boot selection manager. If you are quick after the BIOS stage a MBR F1234> boot selection is prompted: The keystroke F attempts to boot from floppy (/dev/fd0) and any 1/2/3/4 key attempts to bootstrap /dev/hda[number] respectively.

FreeDOS

ELKS boot loader is capable of booting ELKS and a version of FreedDOS for 16 bit computers called Svarog86. Perhaps with sufficient effort DOS 6.20 can also be made to work.

So what worked for installing Svarog86 with ELKS boot loader is formatting with Windows 10 as fat32 and then you need to use Svarog86 sys like that: format e: /S. This will format the partition as fat16 and make the partition Svarog86 bootable. The partition type is reported as "e" for "Win9x fat16 (LBA)" by ELKS fdisk and it is indeed fat16 changed by Svarog86's format command. In ELKS boot loader you can select which partition you want to boot: ELKS or Svarog86 by typing 1,2,3.

Under Svarog86 you may need to provide the location of command.com if you have several drives C:, D:, etc, but it works.

MS-DOS 5.0

To dual-boot MS-DOS 5.0 (other versions might work, not tested) and ELKS, one must consider:

• shrinking an old FAT or MINIX partition is unsupported, so keeping an existing ELKS or DOS system is not an option (yet). This also means you do need MS-DOS boot floppies for this.
• at least the semi-graphical (ASCII art) installer in DOS will not ask you whether any primary partition on y our HDD is worth to be kept. It will override all partitions that it can read and install itself on /dev/hda1 with bootable flag!

Hence, the proven steps need to be in this order:

1. Use your ELKS floppy to boot
2. in fdisk: delete all partitions
3. in fdisk: create two partitions. Use the cylinder count to get a grip on sizes. fdisk will only need this parameter. E.g. my 42 MB HDD has 982 cylinders, I created the first partition from cylinder 0 to cylinder 511 and the second partition from 512 to 982 which makes both roughly the same size.
4. in fdisk: set bootable flag on primary partition #1 if not already
5. in fdisk: write and quit
6. boot the DOS installer disk
7. say Y to everything regarding partitioning, DOS will overwrite both partitions, create FAT on both on them and make the first one bootable.
8. finish DOS installation and reboot with
9. your ELKS floppy booting
10. use fdisk in ELKS again to make the 2nd partition bootable
11. use fdisk to set the 2nd partition to MINIX if wanted
12. write and quit
13. use mkfs on /dev/hda2 for FAT or MINIX
14. use sys to transfer your ELKS system to /dev/hda2
15. finally store away all those floppies and enjoy the dual-boot!