1. Chapter 6: BIOS

2. The Need to Communicate
A PC needs devices such as keyboards and mice to provide input and output devices such as monitors and sound cards to communicate the current state of running programs to you.
Getting the CPU to communicate with a device starts with some kind of interconnection – a communication bus that enables the CPU to send commands to and from devices.

3. MCC – Memory Controller Chip
The MCC or Northbridge is the interconnection between the CPU, and other devices.

4. The Southbridge
Northbridge – deals with high-speed interfaces, i.e. video cards and RAM
Southbridge works with lower speed devices such as USB and hard drive controllers.
The Northbridge and Southbridge controllers are known as the chipset.

5. The Chipset Extends the data bus to every device
Data constantly flows on the external data bus among the CPU chipset, RAM and other devices

6. The Chipset, continued
The first use for the address bus is for the CPU to tell the chipset to send/store data in memory and tell the chipset which section of memory to use.

7. Talking to the Keyboard
In early computers the keyboard was connected to an external data bus via a keyboard controller chip.
The Southbridge now handles the keyboard control functions
The keyboard controller was one of the last single function chips to be absorbed in the chipset.

8. Talking to the Keyboard
Typical Keyboard Controller

9. Scanning Chip
When a keyboard button is pressed, a scanning chip in the keyboard sends a coded pattern of binary numbers to the keyboard controller. This is called a Scan Code.

10. Unique Code
Every keyboard button has its own unique scan code.

11. Keyboard Chip

12. Keyboard Controller
The keyboard controller has its own code book. If it wants to know what last key was last pressed, the CPU needs to know the command that orders the keyboard controller to put the scan code of the letter on the external bus so the CPU can read it.

13. Getting the data

14. BIOS
The CPU needs some sort of support programming loaded into memory that teaches it about a particular device.
That program is called basic input/output services or BIOS

15. BIOS
The programs dedicated to enabling the CPU to communicate with devices are called services (or device drivers)
Every device on a computer needs BIOS

16. Bringing BIOS to the PC
All operating systems have built-in code that knows how to talk to your keyboard, your mouse and every other piece of hardware you connect to your computer.

17. Bringing BIOS to the PC
The perfect place to store the support programming is on the motherboard. The need is for a permanent program storage device that does not depend on peripherals to work.
This storage needs to sit on the motherboard.

18. ROM (on motherboard)
A read-only (ROM) memory chip stores programs called services.
They differ from RAM in that they are non-volatile and they read-only.

19. ROM
Modern motherboards use a type of ROM called flash ROM. It can be updated and the contents can be changed. It stores programs called services.

20. ROM Motherboards contain a flash ROM chip called system ROM.
It contains code that enables the CPU to talk to basic hardware.

21. ROM
It also contains programs for communicating with hard drives, optical drives, display devices, and USB ports

22. ROM
To talk to all of that hardware requires hundreds of little services. The programs stored on the ROM chip of the motherboard are called, collectively, the system BIOS

23. System BIOS Support Two types of hardware BIOS support
System BIOS supports all of the hardware that never changes, such as the keyboard and the speaker (that beeps). The system ROM chip stores the BIOS for these and other devices that never change.
System BIOS supports all of the hardware that might change from time to time. This includes RAM, the HDD, and the SDD.

24. UEFI
The BIOS in modern systems Unified Extensible Firmware Interface has an advantage over older versions, such as:
UEFI supports file systems that enable booting on drives larger than 2.2TB
UEFI supports 32-bit or 64bit booting
UEFI handles all boot-loading duties
UEFI is not dependent on x86 firmware

25. CMOS
Complementary metal-oxide semiconductor chips stores that information that describes specific device parameters. As shown below, it was a separate chip on the motherboard, but now it is built into the Southbridge

26. Modify CMOS: The Setup Program
Every PC has a CMOS setup program or the system setup utility.

27. The End
Thomas Russell
Information Technology Teacher