BUS LINES

Provide data pathways that connect various system components.

Definition of Bus lines

Also known as buses Connects the parts of the CPU to each other. Buses are used to transfer bits from input

devices to memory, from memory to the CPU, from the CPU to memory, and from memory to output or storage devices.

All buses consist of two parts;

i) data bus

ii) address bus

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- Data Bus measured by its size.- The size of a bus called bus width, which is

determines the number of bits that can be transmitted at one time.

Example: A 32-bit bus can transmit 32 bits (four bytes) at a time. On a 64-bit bus, bits are transmitted from one location to another 64 bits (eight bytes) at a time.

- The larger the number of bits handled by the

bus, the faster the computer transfers data.

Highway analogy:

- Assume that one lane on a highway can carry one bit. A 32-bit bus, then, is like a 32-lane highway; and a 64-bit bus is like an 64-lane highway.

Types of Buses

i) System bus- Connects the CPU to main memory on the

system board

ii) Expansion bus

- Allows the CPU to communicate with peripheral devices.

- Types of expansion buses:

ISA, PCI, AGP, USB, and HPSB

Types of expansion buses

a) ISA (Industry Standard Architecture)- The most common and slowest expansion bus.- A mouse, modem cad, sound card, and low speed

network card are examples of devices connect to ISA bus.

b) PCI (Peripheral Component Interconnect)- The PCI bus transfers data about 20 times faster

than ISA bus.- Most computer today have PCI bus- PCI buses was designed to meet the video demands

of graphical user interfaces.

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C) AGP (Accelerated Graphics Port)- Designed by Intel to improve the speed of 3-D

graphics and video performance- AGP is twice as fast as the PCI bus.- AGP is replacing The PCI bus for the transfer of

video data.

d) USB (Universal Serial Bus)- USB is a bus that eliminate the need to install

expansion cards into expansion slots.- USB combines with PCI bus on the system board to

support several external devices without using expansion slots or cards.

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- External USB devices are connected from one to another and then onto the USB bus. The USB bus then connects to the PCI bus on the motherboard.

- USB 1.1 – over twice faster than AGP bus.- USB 2.0 – 40 times faster than USB 1.1

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e) FireWire buses- Also known as high performance serial bus

(HPSB).- Operate much like USB buses and perform at

speeds comparable to USB 2.0.- Fire Wire and USB 2.0 buses are used for

special applications that provide support for digital camcorders and video editing software.