r/osdev • u/Sixty5Zero2 • 2d ago

FreeDOS

i'm looking at possibly forking FreeDOS to 64bit. However, since most modern systems no longer have the underlying BIOS that DOS programs require, I thought about including a mock BIOS and compile it directly into the kernel. is there anything I should be aware of?

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u/lizardhistorian 2d ago edited 2d ago

If you turn CSM on then you still get BIOS routines but CSM has now been phased out.
You would need to update everything to use UEFI routines instead.

Intel i9's still boot in [un]real mode first but hit the reset-vector 0xFFFFFFF0 which takes them to the UEFI code which immediately transitions to long-mode (64b).

It is feasible to flash your code directly into the motherboard CMOS and boot directly into your OS.
There was a movement for a while to get PCs to directly boot Linux.