I think the DOS interrupt is on the high level, BIOS interrupt is lower, and I/O command is the lowest. So all I/O interruptions (include BIOS interrupts) will finally use in/out port commands, am I right? Is it possible to debug or trace into the BIOS interrupt handlers?

hmm,
dos is slower, that is sure, if you use some dos function, instead of bios function, but if you have to talk to hardware, then you must use port commands, no other way to do it.

you can trace real time with softice. can trace interrrupts i remember.
works under win98, and dos well.

sure, you will see many outs and ins.

the reason these hardware level functions are not commonly used, is compatibility, 10 computers may have 10 different chipsets...

remember you have motherboard drivers on your windows too, and video card drivers, etc.

But theres always a standard way to do all things with IN and OUT no? Or does DOS sort it out for each chipset

From what I have read, there is some standardization or backward compatibility with embedded chips. But, it is best to use BIOS level interrupts to do this except in video services and few others.

some things are standardized and can be done in way you described, other don't

ty guys, that explained it