What is Computer Bus: The electrically conducting path along which data is transmitted inside any digital electronic device. A Computer bus consists of a set of parallel conductors, which may be conventional wires, copper tracks on a PRINTED CIRCUIT BOARD, or microscopic aluminum trails on the surface of a silicon chip. Each wire carries just one bit, so the number of wires determines the largest data WORD the bus can transmit: a bus with eight wires can carry only 8-bit data words, and hence defines the device as an 8-bit device.

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A Bus in a computing system is somewhat like a bus on which you travel. Of course, it’s not a pun, a BUS in a computer works in a collection of wires through which all the data can be transmitted from any part of the computer to another. In other words, it is a connection between many computer parts to enable you operates your system efficiently. The latest slot added is PCI Express (PCIe). It was created to replace the AGP and PCI buses. It has a 64-bit data path and a base speed of 133 MHz, but its real performance enhancement was the addition of full duplex architecture. This allowed the card to run at full speed in both directions at the same time. PCI is bus mastered, meaning that all devices can talk to each other without CPU intervention, which increases system performance. PCI slots are white and much shorter than EISA slots.

A computer bus normally has a single word memorycircuit called a LATCH attached to either end, which briefly stores the word being transmitted and ensures that each bit has settled to its intended state before its value is transmitted.

The Computer bus helps the various parts of the PC communicate. If there was no bus, you would have an unwieldy number of wires connecting every part to every other part. It would be like having separate wiring for every light bulb and socket in your house.

We’ll be covering the following topics in this tutorial:

Types of Computer Bus

There are a variety of buses found inside the computer.

Data Bus: The data bus allows data to travel back and forth between the microprocessor (CPU) and memory (RAM).

Address Bus: The address bus carries information about the location of data in memory.

Control Bus: The control bus carries the control signals that make sure everything is flowing smoothly from place to place.

Expansion Bus: If your computer has expansion slots, there’s an expansion bus. Messages and information pass between your computer and the add-in boards you plug in over the expansion bus.

Although this is a bit confusing, these different buses are sometimes together called simply “the bus.” A user can think of the computer’s “bus” as one unit made up of three parts: data, address, and control, even though the three electrical pathways do not run along each other (and therefore don’t really form a single “unit”) within the computer.

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There are different sizes, or widths of data buses found in computers today. A data bus’ width is measured by the number of bits that can travel on it at once. The speed at which its bus can transmit words, that is, its bus BANDWIDTH, crucially determines the speed of any digital device. One way to make a bus faster is to increase its width;

for example a 16-bit bus can transmit two 8-bit words at once, ‘side-by-side’, and so carries 8-bit data twice as fast as an 8-bit bus can. A computer’s CPU will typically contain several buses, often of differing widths, that connect its various subunits. It is common for modern CPUs to use on-chip buses that are wider than the bus they use to communicate with external devices such as memory, and the speed difference between on- and off-chip operations must then be bridged by keeping a reservoir of temporary data in a CACHE. For example many of the Pentium class of processors use 256 bits for their fastest on-chip buses, but only 64 bits for external links.

An 8-bit bus carries data along 8 parallel lines. A 16-bit bus, also called ISA (Industry Standard Architecture), carries data along 16 lines. A 32-bit bus, classified as EISA (Enhanced Industry Standard Architecture) or MCA (Micro Channel Architecture), can carry data along 32 lines.

The speed at which buses conduct signals is measured in megahertz (Mhz). Typical PCs today run at speeds between 20 and 65Mhz. Also see CPU, Expansion Card, Memory, Motherboard, RAM, ROM, and System Unit.

How Does Computer Bus Work?

A bus transfers electrical signals from one place to another. An actual bus appears as an endless amount of etched copper circuits on the motherboard’s surface. The bus is connected to the CPU through the Bus Interface Unit.

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Data travels between the CPU and memory along the data bus. The location (address) of that data is carried along the address bus. A clock signal which keeps everything in synch travels along the control bus.

The clock acts like a traffic light for all the PC’s components; the “green light” goes on with each clock tick. A PC’s clock can “tick” anywhere from 20 to 65 million times per second, which makes it seem like a computer is really fast. But since each task (such as saving a file) is made up of several programmed instructions, and each of those instructions takes several clock cycles to carry out, a person sometimes has to sit and wait for the computer to catch up.

Computer bus is a subsystem that transfers data between components inside a computer or between computers.

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Modern computer buses can use parallel and bit-serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB.

Forward to / Apple / obsolete / obsolete computers / Sun pinouts or follow to 17 MODERN hardware pinouts.
See also RS-232 and other serial ports and interfaces pinouts

• ACR (Advanced Communications Riser)Advanced Communications Riser (ACR) is a slot for connecting a specific hardware, such as AMR hardware, Cable Modem, DSL, Wireless, HomePNA, Ethernet, etc. This slot is a successor to AMR (Audio Modem Riser).
• AGP interfaceAGP (Accelerated Graphics port) is a modified version of PCI bus designed to speed up transfers to video cards.
• ISA busISA=Industry Standard Architecture
• JAMMAJAMMA=Japanese Arcade Machine Manufacturers Association
• PC Card ATA busThis specification makes it possible to share ATA & PC Card with the same connectors.

Apple Pinouts

• ADB Apple Desktop BusADB is a low-speed serial bus used on Apple Macintosh computers manufactured in 1986-1999. It's used to connect input devices (such as the mouse or keyboard) to the CPU
• Apple Communication SlotAvailable on Apple Macintosh 575, 630, 5200 5300 and Apple Performa 6200CD, 6300 series
• Apple Communications Slot IIApple Communications Slot II (PCI Bus Communications Slot)
• Apple II slotExpansion Slot Connector for the Apple II Series Interface/Add On Cards
• Apple IIe I/O slot
• Apple Macintosh portable Processor-Direct Slot (PPDS)
• Apple Macintosh Processor-Direct Slot (PDS)Available on Apple Macintosh SE/30 & IIfx
• NuBusNuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project, and eventually used by Apple Computer and NeXT Computer.
• NuBus 90Available on old Apple Macintosh computers. NuBus with clock rate 20 MHz.

obsolete Pinouts

• Communication and Networking Riser (CNR)The CNR connector is the interface between the motherboard and the CNR board. The connector provides all of the necessary signals to support several different configurations of audio, modem, and/or LAN subsystems in the system
• EISA busThis file is intended to provide a basic functional overview of the EISA Bus, so that hobbyists and amateurs can design their own EISA compatible cards.
• ElectrocoinThe Electrocoin standard was introduced before JAMMA (Japanese Arcade Machine Manufacturers Association) to allow various games to be connected to generic cabinets such as Silverline and Goliaths.
• MCA 16 bit bus
• MCA 32 bit busplus MCA memory-matched extensions, MCA AVEC Auxiliary Video Extension Connector
• VESA LocalBus (VLB)VLB=VESA Local Bus. VESA=Video Electronics Standards Association.

obsolete computers Pinouts

• +4 User portAvailable on Commodore +4 computer.
• Amiga 1000 Ramex
• Amiga 1200 CPU-port
• Amiga Expansion Bus A.K.A Zorro IThese are the connections found at the side of the Amiga 1000 and Amiga 500 computers. They are electric and mechanical compatible with the single exception of being rotated 180 degrees looking at it from the top of the PCB this can cause trouble connecting a expansion meant for the A1000 into the A500 and vice versa. This Bus is like most Buses at this time a extension on the CPU Bus.
• Amiga Expansion Bus Zorro IIThese are the connections found at the side of the Amiga computers. This Bus is like most Buses at this time a extension on the CPU Bus.
• Amiga Expansion Bus Zorro II/III
• C-bus IIDeveloped by Corolla. C-bus II is the successor to C-bus & Extended C-bus.
• CD32 Expansion-port
• Commodore 64 / 128 User I/O
• ECB busThe ECB-bus was defined in 1984 by the german company KONTRON. It was defined of 100x160mm-europa-card and used 2x32 pins (row a and c). Later the third (middle) row of pins was defined for 16-bit-systems. Such bus uses all 3x32pins.
• STEbus STEbus (IEEE-1000)
• UnibusAvailable on the old Digital PDP-11

Sun Pinouts

• SUN SBusSBus is a computer bus system that was used in most SPARC-based computers from Sun Microsystems during the 1990s