BIOS Routine (in short)

• —  The ROM BIOS (Basic Input Output System) is part of the ROM based control system of an IBM PC or compatible that both defines the architecture of the computer to the software.
• —  provides the fundamental I/O services that are needed for the operation of the computer.
• —  The BIOS is actually a collection of procedures.
• —  Each procedure performs a specific function such as reading a character from the keyboard, writing characters to the screen, or reading information from disk.
• —  To call one of these procedures, load required parameters in specified registers and execute an INT N instruction. N in this case is the interrupt type which vectors to the desired type.