__asm{ int portSWITCH_INT_NUMBER } This is from Source\portable\oWotcom\16BitDOS\PC\portmacro.h

portSWITCH_INT_NUMBER 0x80

What does this mean?What is function of this?

It simply puts the assembler instructions:

int 0x80

in your code. This is used to call the scheduler.

Look up the 'int' instruction in an x86 instruction set manual.

Regards.