Computer System Standard Buses

Computer System Standard Buses – The bus is defined as a channel over which information is transferred between two or more devices. The following are the standard buses used in computer systems.

ISA Computer Bus

The ISA stands for Industry Standard Architecture. It is the most common bus in the PC systems. The original ISA bus on the IBM PC was 8-bit wide, reflecting the 8-bit data width of the Intel 8088 processor’s system bus, and ran at 4.77 MHz. It was expanded to 16 bits in 1984 using the Intel 80286. After that, the processor got faster, and eventually data buses got wider, but the compatibility of this bus with existing devices doesn’t allow for more changes to this. The ISA bus provides reasonable throughput for low-bandwidth devices.

STD Computer Bus

The STD stands for Simple To Design and is yet another passive “reach” similar to the PC/AT bus. It is designed by pro-log. It is an 8-bit wide parallel bus accommodating relatively small (4.5 inch x 6.5 inch) circuit cards.

IEEE 488 Standards

The Hewlett-Packard Interface Bus (HPIB) was developed to interface smart test instruments such as digital voltmeters, signal generators, printers, etc., to the computer. In 1875, it was adopted as an IEEE standard, and in 1978, it was revised and named the IEEE 488 standard. This standard defines the communicating devices as talker, listener, and controller. The devices that are capable of putting data on the bus for transmission are named as talkers. Examples for talkers are a digital voltmeter, a frequency counter, etc.

Listeners are devices that are capable of reading data from the bus. Examples for listeners are printers and display devices. The devices that can control the devices to be talker or listener are named as the Controller. It is important to note that one device can be both a talker and a listener. The IEEE 488 standard bus architecture has eight bidirectional data lines. These data lines are supported by three handshake control signals and five general-purpose interface management lines. The data lines are used to transfer data addresses, commands, and status bytes among as many as 8 to 10 instruments.