Saifurs Zero teke Hero. (Spoken Book)

Lesson 6 : Bus Structure

6.1. Learning Objectives

On completion of this lesson you will be able to describe:

i) What is bus structure

ii) Different types of bus structure

iii) Components of different bus.

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6.2. Introduction

Different expansion cards (Display card, Network card etc.) are connected with the motherboard. A card of one company may be connected with a motherboard of another company. So the connection point between the card and the motherboard must be predefined. The predefined structure of connection point is known as the bus standard.

These connectors are also called "expansion slots” as expansion boards must plug into these slots. Some PCs have no slots at all, and so weren't expandable; other machines have three, and most clone-type machines have eight slots. Some machines offer 10 slots.

There are different types of bus structures: PC, ISA, PCI, PCMCIA etc. A card with PCI connection points must be inserted in a PCI expansion slot of the motherboard. Similarly ISA cards are inserted in ISA slots.

6.3. PC Bus

This bus was used in IBM PC. It has 62 lines. These lines are offered to the outside world through a standard connector. Now we shall look at what these 62 lines do.

6.3.1. Data Path

The original PC and XT were based on the 8088 chip. The 8088 had a data path (the "front door") of just 8 bits, so the PC bus only includes eight data lines. That means this bus is "8 bits wide," and so data transfers can only occur in 8-bit chunks on this bus. Expansion slots on a computer with this bus are called "8-bit" slots. Eight of the 62 wires, then, transport data around the computer.