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int 10h
That is a key thing. It amounts to an indirect call of some particular function, of which there are normally many. If your boot process is not setting those up, but the MenuetOS thing is, that's one significant difference. A number of those wind up calling functions that live in the BIOS, others call functions that have to be loaded into the system (such as the large number of MSDOS calls that were available after a system booted MSDOS). I have not looked under the hood in years, but those software interrupts used to live in the memory beginning at location 0 (real memory address). Each storage location was considered a vector. That is, it contained the address of some function to execute. One could replace the vector with one's own function address and then call the old vector when one's function was done. This was a way to chain in things like timer functions, TSR apps, etc.
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