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I have downloaded your DOS 6.22 with CD support, extracted all files and everything is fine. I now want to make a bootable CD or USB.
Is this possible, please?
AFAIK, MS-DOS was not made to boot from optical disk (CD/DVD) or USB (except MS-DOS 7.1, which does work on CD), it's only for floppy disks. Floppy disks were what people used back in the 80's and early 90's for installing media on computers. Optical disks were not fully mainstream until about 1993 or 94, when operating systems, software, and other computer media started being sold on CD. So with that said, you already have the installation media extracted from your 7z file, but it's in the IMG format, the disk image file format used for floppy images, and it's most likely bootable.
I don't know. But if you try making MSCDEX and making floppy boot work in CD Boot, it might work. Sorry i am doing good at Lua, not how DOS is made (it might be assembly)
Actually in both cases making bootable image is trivial: you just embed your floppy image into larger CD or USB image. Use mkisofs -b option for that (other programs would surely support other options) and RMPrepUSB for USB.
What's tricky - is to provide support for the USB and CD itself! Because by default BIOS would just emulate that mini-floppy for you... and that's it. Your MS DOS would boot perfectly fine... except it wouldn't see the CD and/or USB it just booted from!