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Thursday, 12 July 2012

A complete lecture on BUS


When referring to a computer, the bus also known as the address bus, data bus, or local bus is a data connection between two or more devices connected together. For example a bus enables a computer processor to communicate with the memory or a video card to communicate with the memory.
A bus is capable of being (parallel or a serial bus), (Synchronized or Asynchronized) and today all computers utilize two types of buses, an internal or local bus and an external bus. An internal bus enables a communication between internal components such as a computer video card and memory (e.g. ISA, EISA, PCI, AGP, etc.) and an external bus is capable of communicating with external components such as a SCSI bus, CAN, CAMAC, GPIB, etc.
A computer or devices bus speed or throughput is always measured in bits per second or megabytes per second.
The bus is not only cable connection but also hardware (bus architecture), protocol, software, and bus controller

BUS Basics

A computer bus is a method of transmitting data from one part of the computer to another part of the computer. The computer bus connects all devices to the computer CPU and main memory. The computer bus consists of three parts the address bus, a data bus and control bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go. The control bus exchanges all control signals. The following part contains a brief overview on each of the computer buses.


1- PnP

Short for Plug and Play, PnP is an ability of a computer to detect and configure a new piece of hardware automatically, without the requirement of the user to physically configure the hardware device with jumpers or dipswitches. Plug and Play was introduced on IBM compatible computers with the release of Microsoft Windows 95, where Apple Macintosh computers have always supported the ability to automatically detect and install hardware.
For Plug and Play to operate properly on IBM compatible computers the user must have the following:
• BIOS supporting Plug and Play.
• Operating systems supporting PnP.
• Peripheral with PnP support.
Today all new computers have PnP capabilities. Computers running Microsoft Windows XP no longer support non PnP devices.

2- Throughput (Baud-rate, Speed)

Also known as "communication speed", throughput is a numerical value used to illustrate the total amount of data transferred being transferred through the computer or device at that given time. This number is commonly represented in bits per second (bps) or bytes per second (Bps).

3- Proprietary

Term used to describe a product that is only compatible with a specific type of hardware, software, computer or manufacturer. When referring to computer hardware, it is recommended that you do not choose a proprietary device as it reduces compatibility and generally the capability of upgrading that product in the future.


Introduced by IBM, ISA or Industry Standard Architecture was originally an 8-bit bus that was later expanded to a 16-bit bus in 1984. When this BUS was originally released it was a proprietary BUS, which allowed only IBM to create peripherals and the actual interface. However in the early 1980's other manufacturers were creating the bus.
In 1993, Intel and Microsoft introduced a PnP ISA bus that allowed the computer to automatically detect and setup computer ISA peripherals such as a modem or sound card. Using the PnP technology an end-user would have the capability of connecting a device and not having to configure the device using jumpers or dipswitches.
To determine if an ISA card is an 8-bit or 16-bit card physically look at the card. You will notice that the first portion of the slot closest to the back of the card is used if the card is an 8-bit card. However, if both sections of the card are being utilized the card is a 16-bit card.
Many manufacturers are trying to eliminate the usage of the ISA slots however for backwards compatibility you may find 1 or 2 ISA slots with additional PCI slots, AGP slots, etc. However, today you may also have a motherboard that has no ISA slots. We highly recommend when purchasing any new internal expansion card that you stay away from ISA as it has for the most part disappeared.


Short for Micro Channel Architecture, MCA was introduced by IBM in 1987, MCA or the Micro Channel bus was a competition for ISA BUS. The MCA bus offered several additional features over the ISA such as a 32-bit bus, automatically configure cards (similar to what Plug and Play is today), and bus mastering for greater efficiency.
One of the major downfalls of the MCA bus was it being a proprietary BUS and because of competing BUS designs. The MCA BUS never became widely used and has since been fazed out of the desktop computers.


Short for Extended Industry Standard Architecture, EISA was announced September of 1988. EISA is a computer bus designed by 9 competitors to compete with IBM's MCA BUS. These competitors were AST Research, Compaq, Epson, Hewlett Packard, NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems.
The EISA Bus provided 32-bit slots at an 8.33 MHz cycle rate for the use with 386DX, or higher processors. In addition the EISA can accommodate a 16-bit ISA card in the first row.
Unfortunately, while the EISA bus is backwards compatible and is not a proprietary bus the EISA bus never became widely used and is no longer found in computers today.


Introduced by Intel in 1992, revised in 1993 to version 2.0, and later revised in 1995 to PCI 2.1. PCI is short for Peripheral Component Interconnect and is a 32-bit computer bus that is also available as a 64-bit bus today. The PCI bus is the most commonly used and found bus in computers today.


Mini PCI is a new standard which measures at 2.75-inch x 1.81-inch x 0.22-inch is a new standard developed by leading notebook manufactures. This technology could allow manufactures to lower their price as the motherboards would be simpler to design.
Type I - Identical to Type II, except requires extra cables for connectors like the RJ-11 and RJ-45. However, offers more flexibility to where it can be placed in the computer.
Type II - Used when size is not important. Type II is able to integrate the RJ-11 and RJ-45 connectors and due away with extra cables.
Type III - SO-DIMM style connector that can be installed with a mere 5 mm overall height above the system board. In addition cabling to the I/O connectors allow Type III cards to be placed anywhere in the system.


PCI-X is a high performance bus that is designed to meet the increased I/O demands of technologies such as Fiber Channel, Gigabit Ethernet and Ultra3 SCSI. PCI-X capabilities include:
• Up to 133 MHz bus speed
• 64-Bit bandwidth
• 1GB/sec throughput
• More efficient bus operation for easier interface.
• Split Transactions allows an indicator device to make only one data request and relinquish the bus. Instead of constantly needing to poll the bus for a response.
• Byte Count that enables indicator to specify in advance the specific number of bytes requested, eliminating the inefficiency of speculative prefetches.
• Backwards compatibility


Introduced by Intel in 1997, AGP or Advanced Graphic Port is a 32-bit bus designed for the high demands of 3-D graphics. AGP has a direct line to the computers memory which allows 3-D elements to be stored in the system memory instead of the video memory.
For AGP to work in a computer must have the AGP slot which comes with most Pentium II and Pentium III machines. The computer also needs to be running Windows 95 OSR2.1, Windows 98, Windows 98 SE, Windows 2000, Windows ME or higher.


USB (Universal Serial Bus) is a new external bus developed by Intel, Compaq, DEC, IBM, Microsoft, NEC and Northern Telcom and released to the public in 1996 with the Intel 430HX Triton II Mother Board. USB has the capability of transferring 12 Mbps, supporting up to 127 devices and only utilizing one IRQ. For PC computers to take advantage of USB the user must be running Windows 95 OSR2, Windows 98 or Windows 2000. Linux users also have the capability of running USB with the proper support drivers installed.


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