Real Mode
When generating a software interrupt, the processor calls one of the 256 functions pointed to by the interrupt address table, which is located in the first 1024 bytes of memory while in real mode (See Interrupt vector). It is therefore entirely possible to use a far-call instruction to start the interrupt-function manually after pushing the flag register.
One of the most useful DOS software interrupts was interrupt 0x21. By calling it with different parameters in the registers (mostly ah and al) you could access various IO operations, string output and more.
Most Unix systems and derivatives do not use software interrupts, with the exception of interrupt 0x80, used to make system calls. This is accomplished by entering a 32-bit value corresponding to a kernel function into the EAX register of the processor and then executing INT 0x80.
Read more about this topic: INT (x86 Instruction)
Famous quotes containing the words real and/or mode:
“That is the real pivot of all bourgeois consciousness in all countries: fear and hate of the instinctive, intuitional, procreative body in man or woman. But of course this fear and hate had to take on a righteous appearance, so it became moral, said that the instincts, intuitions and all the activities of the procreative body were evil, and promised a reward for their suppression. That is the great clue to bourgeois psychology: the reward business.”
—D.H. (David Herbert)
“The character of the logger’s admiration is betrayed by his very mode of expressing it.... He admires the log, the carcass or corpse, more than the tree.... What right have you to celebrate the virtues of the man you murdered?”
—Henry David Thoreau (1817–1862)