Learning Objectives

B I O S Basic Input / Output System

PC's Hypothalamus

CPU’s brain

B I O S

• When you first turn on your PC
• Your PC requires information
• to detect PC components
• To find the operating system(floppy disk, hard drive, or a CD-ROM)
• This information is stored in the BIOS

Power on

• When a computer is turned on, the microprocessor has no idea what to do next as there is nothing at all in the memory to execute, it tries to execute its first instruction and it has to get the instruction from somewhere.
• BIOS provides those instructions and it is stored in a BIOS ROM.
• The instruction typically located at memory location FFFF0h, or right at the end of the system memory
• This process is known as booting, or booting up, which is short for bootstrapping
• The whole process is hidden because the only thing displayed by the monitor is the logo of the machine manufacturer or the logo of the bios company.

BIOS Functions

Power-on Self Test ( POST ) - Takes place right after you power on. It will test computer hardware, ensuring hardware is properly functioning before starting process of loading operating system. If the POST is successful, the BIOS calls INT 19 (Interrupt 19) and then proceeds to look for devices attached to the motherboard.

Bootstrap Loader - Process of locating the operating system. If capable operating system located, BIOS will pass the control to it.

Bootstrapping

• Tests the system and prepares the computer for operation based on CMOS settings (installed hardware and the configuration settings from the manufacturer and user)
• Load the interrupt handlers and device drivers

Interrupt handlers - Small pieces of software that act as a translator between the hardware components and the operating system.

Device drivers – other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive or floppy drive.