Computer bus - AbsoluteAstronomy.com

Computer architecture

In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....

, a bus is a subsystem that transfers data between components inside a computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

, or between computers.

Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus. Modern computer buses can use both parallel and bit serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain

Daisy chain (electrical engineering)

In electrical and electronic engineering a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring...

topology, or connected by switched hubs, as in the case of USB

Universal Serial Bus

USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....

First generation

Early computer

Computer

buses were bundles of wire that attached computer memory

Computer memory

In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...

and peripherals. Anecdotally termed the "digit trunk", they were named after electrical power buses, or busbar

Busbar

In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....

s. Almost always, there was one bus for memory, and another for peripherals, and these were accessed by separate instructions, with completely different timings and protocols.

One of the first complications was the use of interrupt

Interrupt

In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....

s. Early computer programs performed I/O

Input/output

In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...

by waiting in a loop

Busy waiting

In software engineering, busy-waiting or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input is available, or if a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary...

for the peripheral to become ready. This was a waste of time for programs that had other tasks to do. Also, if the program attempted to perform those other tasks, it might take too long for the program to check again, resulting in loss of data. Engineers thus arranged for the peripherals to interrupt the CPU. The interrupts had to be prioritized, because the CPU can only execute code for one peripheral at a time, and some devices are more time-critical than others.
To provide modularity, memory and I/O buses can be combined into a unified system bus

System bus

A system bus is a single computer bus that connects the major components of a computer system. The technique was developed to reduce costs and improve modularity....

.
Digital Equipment Corporation

Digital Equipment Corporation

Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

(DEC) further reduced cost for mass-produced minicomputer

Minicomputer

A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...

s, and mapped peripherals

Memory-mapped I/O

Memory-mapped I/O and port I/O are two complementary methods of performing input/output between the CPU and peripheral devices in a computer...

into the memory bus, so that the input and output devices appeared to be memory locations. This was implemented in the Unibus

Unibus

The Unibus was the earliest of several computer bus technologies used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.-History:...

of the PDP-11

PDP-11

The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...

around 1969.

Later computer programs began to share memory common to several CPUs. Access to this memory bus had to be prioritized, as well.
The classic, simple way to prioritize interrupts or bus access was with a daisy chain

Daisy chain (electrical engineering)

In electrical and electronic engineering a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring...

.

Early microcomputer

Microcomputer

A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers...

bus systems were essentially a passive backplane

Backplane

A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...

connected directly or through buffer amplifiers to the pins of the CPU

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

. Memory and other devices would be added to the bus using the same address and data pins as the CPU itself used, connected in parallel. Communication was controlled by the CPU, which had read and written data from the devices as if they are blocks of memory, using the same instructions, all timed by a central clock controlling the speed of the CPU. Still, devices interrupt

Interrupt

In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....

ed the CPU by signaling on separate CPU pins.

For instance, a disk drive controller would signal the CPU that new data was ready to be read, at which point the CPU would move the data by reading the "memory location" that corresponded to the disk drive. Almost all early microcomputers were built in this fashion, starting with the S-100 bus

S-100 bus

The S-100 bus or Altair bus, IEEE696-1983 , was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer...

in the Altair 8800

Altair 8800

The MITS Altair 8800 was a microcomputer design from 1975 based on the Intel 8080 CPU and sold by mail order through advertisements in Popular Electronics, Radio-Electronics and other hobbyist magazines. The designers hoped to sell only a few hundred build-it-yourself kits to hobbyists, and were...

computer system.

In some instances, most notably in the IBM PC

IBM PC

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...

, although similar physical architecture can be employed, instructions to access peripherals (in and out) and memory (mov and others) have not been made uniform at all, and still generate distinct CPU signals, that could be used to implement a separate I/O bus.

These simple bus systems had a serious drawback when used for general-purpose computers. All the equipment on the bus has to talk at the same speed, as it shared a single clock.

Increasing the speed of the CPU becomes harder, because the speed of all the devices must increase as well. When it is not practical or economical to have all devices as fast as the CPU, the CPU must either enter a wait state

Wait state

A wait state is a delay experienced by a computer processor when accessing external memory or another device that is slow to respond.As of late 2011, computer microprocessors run at very high speeds, while memory technology does not seem to be able to catch up: typical PC processors like the Intel...

, or work at a slower clock frequency temporarily, to talk to other devices in the computer. While acceptable in embedded systems, this problem was not tolerated for long in general-purpose, user-expandable computers.

Such bus systems are also difficult to configure when constructed from common off-the-shelf equipment. Typically each added expansion card

Expansion card

The expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard or backplane to add functionality to a computer system via the expansion bus.One edge of the expansion card holds the contacts that fit exactly into the slot...

requires many jumpers

Jumper (computing)

In electronics and particularly computing, a jumper is a short length of conductor used to close a break in or bypass part of an electrical circuit...

in order to set memory addresses, I/O addresses, interrupt priorities, and interrupt numbers.

Second generation

"Second generation" bus systems like NuBus

NuBus

NuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project. The first complete implementation of the NuBus and the NuMachine was done by Western Digital for their NuMachine, and for the Lisp Machines Inc. LMI-Lambda. The NuBus was later...

addressed some of these problems. They typically separated the computer into two "worlds", the CPU and memory on one side, and the various devices on the other. A bus controller accepted data from the CPU side to be moved to the peripherals side, thus shifting the communications protocol burden from the CPU itself. This allowed the CPU and memory side to evolve separately from the device bus, or just "bus". Devices on the bus could talk to each other with no CPU intervention. This led to much better "real world" performance, but also required the cards to be much more complex. These buses also often addressed speed issues by being "bigger" in terms of the size of the data path, moving from 8-bit parallel buses in the first generation, to 16 or 32-bit in the second, as well as adding software setup (now standardised as Plug-n-play) to supplant or replace the jumpers.

However these newer systems shared one quality with their earlier cousins, in that everyone on the bus had to talk at the same speed. While the CPU was now isolated and could increase speed without fear, CPUs and memory continued to increase in speed much faster than the buses they talked to. The result was that the bus speeds were now very much slower than what a modern system needed, and the machines were left starved for data. A particularly common example of this problem was that video card

Video card

A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...

s quickly outran even the newer bus systems like PCI, and computers began to include AGP

Accelerated Graphics Port

The Accelerated Graphics Port is a high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics. Since 2004 AGP has been progressively phased out in favor of PCI Express...

just to drive the video card. By 2004 AGP was outgrown again by high-end video cards and other peripherals and has been replaced by the new PCI Express

PCI Express

PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...

bus.

An increasing number of external devices started employing their own bus systems as well. When disk drives were first introduced, they would be added to the machine with a card plugged into the bus, which is why computers have so many slots on the bus. But through the 1980s and 1990s, new systems like SCSI

SCSI

Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

and IDE were introduced to serve this need, leaving most slots in modern systems empty. Today there are likely to be about five different buses in the typical machine, supporting various devices.

Third generation

"Third generation" buses have been emerging into the market since about 2001, including HyperTransport

HyperTransport

HyperTransport , formerly known as Lightning Data Transport , is a technology for interconnection of computer processors. It is a bidirectional serial/parallel high-bandwidth, low-latency point-to-point link that was introduced on April 2, 2001...

and InfiniBand

InfiniBand

InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...

. They also tend to be very flexible in terms of their physical connections, allowing them to be used both as internal buses, as well as connecting different machines together. This can lead to complex problems when trying to service different requests, so much of the work on these systems concerns software design, as opposed to the hardware itself. In general, these third generation buses tend to look more like a network

Computer network

A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

than the original concept of a bus, with a higher protocol overhead needed than early systems, while also allowing multiple devices to use the bus at once.

Buses such as Wishbone

Wishbone (computer bus)

The Wishbone Bus is an open source hardware computer bus intended to let the parts of an integrated circuit communicate with each other. The aim is to allow the connection of differing cores to each other inside of a chip...

have been developed by the open source hardware

Open source hardware

Open source hardware consists of physical artifacts of technology designed and offered in the same manner as free and open source software . Open source hardware is part of the open source culture movement and applies a like concept to a variety of components. The term usually means that...

movement in an attempt to further remove legal and patent constraints from computer design.

Description of a bus

At one time, "bus" meant an electrically parallel system, with electrical conductors similar or identical to the pins on the CPU. This is no longer the case, and modern systems are blurring the lines between buses and networks.

Buses can be parallel buses

Parallel communications

In telecommunication and computer science, parallel communication is a method of sending several data signals simultaneously over several parallel channels...

, which carry data words in parallel on multiple wires, or serial buses, which carry data in bit-serial form. The addition of extra power and control connections, differential drivers, and data connections in each direction usually means that most serial buses have more conductors than the minimum of one used in the 1-Wire

1-Wire

1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single signal. 1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive...

and UNI/O

UNI/O

The UNI/O bus is an asynchronous serial bus created by Microchip Technology for low speed communication in embedded systems. The bus uses a master/slave configuration, requiring one signal to pass data between devices...

serial buses. As data rates increase, the problems of timing skew, power consumption, electromagnetic interference and crosstalk across parallel buses become more and more difficult to circumvent. One partial solution to this problem has been to double pump the bus. Often, a serial bus can actually be operated at higher overall data rates than a parallel bus, despite having fewer electrical connections, because a serial bus inherently has no timing skew or crosstalk. USB

Universal Serial Bus

, FireWire, and Serial ATA

Serial ATA

Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...

are examples of this. Multidrop connections do not work well for fast serial buses, so most modern serial buses use daisy-chain or hub designs.

Most computers have both internal and external buses. An internal bus connects all the internal components of a computer to the motherboard (and thus, the CPU

Central processing unit

and internal memory). These types of buses are also referred to as a local bus

Local bus

In computer science, a local bus is a computer bus that connects directly, or almost directly, from the CPU to one or more slots on the expansion bus. The significance of direct connection to the CPU is avoiding the bottleneck created by the expansion bus, thus providing fast throughput...

, because they are intended to connect to local devices, not to those in other machines or external to the computer. An external bus connects external peripherals to the motherboard.

Network

Computer network

connections such as Ethernet

Ethernet

Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

are not generally regarded as buses, although the difference is largely conceptual rather than practical. The arrival of technologies such as InfiniBand

InfiniBand

and HyperTransport

HyperTransport

is further blurring the boundaries between networks and buses. Even the lines between internal and external are sometimes fuzzy, I²C

I²C

I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...

can be used as both an internal bus, or an external bus (where it is known as ACCESS.bus

ACCESS.bus

ACCESS.bus is a peripheral-interconnect computer bus developed by Philips in the early 1990s. It is similar in purpose to USB, in that it allows low-speed devices to be added or removed from a computer on the fly...

), and InfiniBand is intended to replace both internal buses like PCI as well as external ones like Fibre Channel

Fibre Channel

Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...

. In the typical desktop application, USB

Universal Serial Bus

serves as a peripheral bus, but it also sees some use as a networking utility and for connectivity between different computers, again blurring the conceptual distinction.

Bus topology

In a network, the master scheduler controls the data traffic. If data is to be transferred, the requesting computer sends a message to the scheduler, which puts the request into a queue. The message contains an identification code which is broadcast to all nodes of the network. The scheduler works out priorities and notifies the receiver as soon as the bus is available.

The identified node takes the message and performs the data transfer between the two computers. Having completed the data transfer the bus becomes free for the next request in the scheduler's queue.

Advantage: Any computer can be accessed directly and messages can be sent in a relatively simple and fast way.
Disadvantage: A scheduler is required to organize the traffic by assigning frequencies and priorities to each signal.

Parallel

ASUS Media Bus
Asus Media Bus
The Asus Media Bus is a proprietary computer bus developed by Asus, which was used on some Socket 7 motherboards in the middle 1990s. It is a combined PCI and ISA slot. Expansion cards supporting this interface were only manufactured by Asus for a very limited time...

proprietary, used on some ASUS
ASUS
ASUSTeK Computer Incorporated is a multinational computer technology and consumer electronics product manufacturer headquartered in Taipei, Taiwan. Its product range includes motherboards, desktops, laptops, monitors, tablet PCs, servers and mobile phones...

Socket 7
Socket 7
Socket 7 is a physical and electrical specification for an x86-style CPU socket on a personal computer motherboard. The socket supersedes the earlier Socket 5, and accepts P5 Pentium microprocessors manufactured by Intel, as well as compatibles made by Cyrix/IBM, AMD, IDT and others.Socket 7 was...

motherboards
Computer Automated Measurement and Control (CAMAC) for instrumentation systems
Extended ISA or EISA
Industry Standard Architecture
Industry Standard Architecture
Industry Standard Architecture is a computer bus standard for IBM PC compatible computers introduced with the IBM Personal Computer to support its Intel 8088 microprocessor's 8-bit external data bus and extended to 16 bits for the IBM Personal Computer/AT's Intel 80286 processor...

or ISA
Low Pin Count
Low Pin Count
The Low Pin Count bus, or LPC bus, is used on IBM-compatible personal computers to connect low-bandwidth devices to the CPU, such as the boot ROM and the "legacy" I/O devices . The "legacy" I/O devices usually include serial and parallel ports, PS/2 keyboard, PS/2 mouse, floppy disk controller...

or LPC
MBus
MicroChannel
Microchannel
Microchannel can refer to* Basic structure used in microtechnology, see Microchannel .* Micro Channel architecture in computing...

or MCA
Multibus
Multibus
Multibus is a computer bus standard used in industrial systems. It was developed by Intel Corporation and was adopted as the IEEE 796 bus.The Multibus specification was important because it was a robust, well-thought out industry standard with a relatively large form factor so complex devices could...

for industrial systems
NuBus
NuBus
NuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project. The first complete implementation of the NuBus and the NuMachine was done by Western Digital for their NuMachine, and for the Lisp Machines Inc. LMI-Lambda. The NuBus was later...

or IEEE 1196
OPTi local bus used on early Intel 80486
Intel 80486
The Intel 80486 microprocessor was a higher performance follow up on the Intel 80386. Introduced in 1989, it was the first tightly pipelined x86 design as well as the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating point unit...

motherboards.
Conventional PCI
Parallel ATA (aka Advanced Technology Attachment, ATA, PATA, IDE, EIDE, ATAPI, etc.) disk/tape peripheral attachment bus
S-100 bus
S-100 bus
The S-100 bus or Altair bus, IEEE696-1983 , was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer...

or IEEE 696, used in the Altair and similar microcomputers
SBus
SBus
SBus is a computer bus system that was used in most SPARC-based computers from Sun Microsystems and others during the 1990s...

or IEEE 1496
SS-50 Bus
SS-50 Bus
The SS-50 bus was an early computer bus designed as a part of the SWTPC 6800 Computer System that used the Motorola 6800 CPU. The SS-50 motherboard would have around seven 50-pin connectors for CPU and memory boards plus eight 30-pin connectors for I/O boards...
Runway bus
Runway bus
The Runway bus is a front side bus developed by Hewlett-Packard for use by its PA-RISC microprocessor family. The Runway bus is a 64-bit wide, split transaction, time multiplexed address and data bus running at 120 MHz...

, a proprietary front side CPU bus developed by Hewlett-Packard for use by its PA-RISC microprocessor family
GSC/HSC
GSC bus
GSC is a bus used in many of the HP 9000 workstations and servers. The acronym has various explanations, including Gecko System Connect , Gonzo System Connect and General System Connect....

, a proprietary peripheral bus developed by Hewlett-Packard for use by its PA-RISC microprocessor family
Precision Bus
HP Precision Bus
The HP Precision bus is the data transfer bus of the proprietary Hewlett Packard architecture HP 3000. This bus gives a 32 bits data path with an 8 MHz clock. It supports a maximum transfer rate of 23 MB/s in burst mode...

, a proprietary bus developed by Hewlett-Packard for use by its HP3000 computer family
STEbus
STEbus
The STEbus is a non-proprietary, processor-independent, bus with 8 data lines and 20 address lines. It was popular for industrial control systems in the late 1980s and early 1990s before the ubiquitous IBM PC dominated this market....
STD Bus
STD Bus
STD Bus is a computer bus popular with industrial control applications but has also been used in computing applications. The STD Bus has been called "STD-80" as well: this has created a popular confusion that the bus contains 80 pins; however, it refers to its bus being related to the Zilog Z80...

(for STD-80 [8-bit] and STD32 [16-/32-bit]), FAQ
Unibus
Unibus
The Unibus was the earliest of several computer bus technologies used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.-History:...

, a proprietary bus developed by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

for their PDP-11
PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...

and early VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...

computers.
Q-Bus
Q-Bus
The Q-bus was one of several bus technologies used with PDP and MicroVAX computer systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts....

, a proprietary bus developed by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

for their PDP
Programmed Data Processor
Programmed Data Processor was the name of a series of minicomputers made by Digital Equipment Corporation. The name 'PDP' intentionally avoided the use of the term 'computer' because, at the time of the first PDPs, computers had a reputation of being large, complicated, and expensive machines, and...

and later VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...

computers.
VESA Local Bus
VESA Local Bus
The VESA Local Bus was mostly used in personal computers. VESA Local Bus worked alongside the ISA bus; it acted as a high-speed conduit for memory-mapped I/O and DMA, while the ISA bus handled interrupts and port-mapped I/O.-Historical overview:In the early 1990s, the I/O bandwidth of...

or VLB or VL-bus
VMEbus
VMEbus
VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...

, the VERSAmodule Eurocard bus
PC/104
PC/104
PC/104 is an embedded computer standard controlled by the which defines both a form factor and computer bus. PC/104 is intended for specialized embedded computing environments where applications depend on reliable data acquisition despite an often extreme environment...
PC/104 Plus
PC/104 Express
PCI-104
PCIe-104
Zorro II
Zorro II
Zorro II is the name of the general purpose expansion bus used by the Amiga 2000 computer. The bus is mainly a buffered extension of the Motorola 68000 bus, with support for bus mastering DMA. The expansion slots use a 100-pin connector and the card form factor is the same as the IBM PC...

and Zorro III
Zorro III
Released as the expansion bus of the Commodore Amiga 3000 in 1990, the Zorro III computer bus was used to attach peripheral devices to an Amiga motherboard. Designed by Commodore International lead engineer Dave Haynie, the 32-bit Zorro III replaced the 16-bit Zorro II bus used in the Amiga 2000...

, used in Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...

computer systems

Serial

1-Wire
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single signal. 1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive...
HyperTransport
HyperTransport
HyperTransport , formerly known as Lightning Data Transport , is a technology for interconnection of computer processors. It is a bidirectional serial/parallel high-bandwidth, low-latency point-to-point link that was introduced on April 2, 2001...
I²C
I²C
I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
PCI Express
PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...

or PCIe
Serial ATA
Serial ATA
Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...

(SATA)
Serial Peripheral Interface Bus
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...

or SPI bus
UNI/O
UNI/O
The UNI/O bus is an asynchronous serial bus created by Microchip Technology for low speed communication in embedded systems. The bus uses a master/slave configuration, requiring one signal to pass data between devices...
SMBus
System Management Bus
The System Management Bus is a single-ended simple two-wire bus for the purpose of lightweight communication...

Self-repairable

Self-repairable elastic interface bus

Elastic interface bus

Elastic Interface buses, abbreviated as EI bus connections, can be generalized as bus connections which are high speed interfaces that send clock signals with data.-Description:...

es have recently been invented by IBM

IBM

International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

. IBM has filed a patent

Patent

A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

application on these buses which is undergoing peer review on Peer-to-Patent. The public commentary period closed on July 24, 2008. The IBM invention provides a spare net which the system switches to in the event that an alternate net doesn't function.

Parallel

HIPPI
HIPPI
HIPPI is a computer bus for the attachment of high speed storage devices to supercomputers. It was popular in the late 1980s and into the mid-to-late 1990s, but has since been replaced by ever-faster standard interfaces like SCSI and Fibre Channel.The first HIPPI standard defined a 50-wire...

HIgh Performance Parallel Interface
IEEE-488
IEEE-488
IEEE-488 is a short-range digital communications bus specification. It was created for use with automated test equipment in the late 1960s, and is still in use for that purpose. IEEE-488 was created as HP-IB , and is commonly called GPIB...

(aka GPIB, General-Purpose Interface Bus, and HPIB, Hewlett-Packard Instrumentation Bus)
PC Card
PC Card
In computing, PC Card is the form factor of a peripheral interface designed for laptop computers. The PC Card standard was defined and developed by the Personal Computer Memory Card International Association which itself was created by a number of computer industry companies in the United States...

, previously known as PCMCIA, much used in laptop computers and other portables, but fading with the introduction of USB and built-in network and modem connections

Serial

USB
Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....

Universal Serial Bus, used for a variety of external devices
Controller area network
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....

("CAN bus")
EIA-485
eSATA
IEEE 1394 interface
IEEE 1394 interface
The IEEE 1394 interface is a serial bus interface standard for high-speed communications and isochronous real-time data transfer, frequently used by personal computers, as well as in digital audio, digital video, automotive, and aeronautics applications. The interface is also known by the brand...

(FireWire)

Examples of internal/external computer buses

Futurebus
Futurebus
Futurebus is a computer bus standard, intended to replace all local bus connections in a computer, including the CPU, memory, plug-in cards and even, to some extent, LAN links between machines. The effort started in 1979 and didn't complete until 1987, and then immediately went into a redesign...
InfiniBand
InfiniBand
InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...
QuickRing
QuickRing
QuickRing was a gigabit-rate interconnect that combined the functions of a computer bus and a network. It was designed at Apple Computer as a multimedia system to run "on top" of existing local bus systems inside a computer, but was later taken over by National Semiconductor and repositioned as an...
Scalable Coherent Interface (SCI)
SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

Small Computer System Interface, disk/tape peripheral attachment bus
Serial Attached SCSI
Serial Attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...

(SAS) and other serial SCSI buses
Yapbus, a proprietary bus developed for the Pixar Image Computer
Pixar Image Computer
The Pixar Image Computer was a graphics designing computer originally developed by the Computer Division of Lucasfilm, later renamed Pixar after being purchased by Steve Jobs on February 3, 1986. The name Pixar, which was coined by Alvy Ray Smith, Loren Carpenter and Rodney Stock, is a made-up...

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

First generation

Second generation

Third generation

Description of a bus

Bus topology

Parallel

Serial

Self-repairable

Parallel

Serial

Examples of internal/external computer buses

See also

External links