Dual boot ELKS and DOS

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.