Chapter 6: BIOS

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.

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

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.

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

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.

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.

Talking to the Keyboard Typical Keyboard Controller

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.

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

Keyboard Chip

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.

Getting the data

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

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

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.

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.

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.

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.

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

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

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

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.

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

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

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

The End Thomas Russell Information Technology Teacher