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Encyclopedia > Bus (computing)
PCI Express bus card slots (from top to bottom: x4, x16, x1 and x16), compared to a traditional 32-bit PCI bus card slot (bottom). Their resemblance to school buses is merely a coincidence.

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus can logically connect several peripherals over the same set of wires. Each bus defines its set of connectors to physically plug devices, cards or cables together. ImageMetadata File history File links Download high resolution version (927x629, 449 KB) PCI Express x4, x16 and x1 slots, as well as a standard 32-bit PCI slot. ... ImageMetadata File history File links Download high resolution version (927x629, 449 KB) PCI Express x4, x16 and x1 slots, as well as a standard 32-bit PCI slot. ... This article does not cite any references or sources. ... A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... This article is about the machine. ... A point-to-point link is an exclusive connection between addressable units. ... A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. ... For an account of the words periphery and peripheral as they are used in biology, sociology, politics, computer hardware, and other fields, see the periphery disambiguation page. ... Look up connector in Wiktionary, the free dictionary. ...


Early computer buses were literally parallel electrical buses 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 topology, or connected by switched hubs, as in the case of USB. An electrical bus (sometimes spelled buss) is a physical electrical interface where many devices share the same electric connection. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The elementary meaning of daisy chain is a garland created from the daisy flower, generally as a childrens game. ... USB redirects here. ...

Contents

History

First generation

Early computer buses were bundles of wire that attached memory and peripherals. They were named after electrical buses, or busbars. Almost always, there was one bus for memory, and another for peripherals,[citation needed] and these were accessed by separate instructions, with completely different timings and protocols. This article is about the machine. ... This article does not cite any references or sources. ... An electrical bus (sometimes spelled buss) is a physical electrical interface where many devices share the same electric connection. ...


One of the first complications was the use of interrupts. Early computers performed I/O by waiting in a loop 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. In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ... Energy Input: The energy placed into a reaction. ...


Some time after this, some computers began to share memory among several CPUs. On these computers, access to the bus had to be prioritized, as well.


The classic, simple way to prioritize interrupts or bus access was with a daisy chain. The elementary meaning of daisy chain is a garland created from the daisy flower, generally as a childrens game. ...


DEC noted that having two buses seemed wasteful and expensive for mass-produced minicomputers, and mapped peripherals into the memory bus, so that the devices appeared to be memory locations. Digital Equipment Corporation was a pioneering American company in the computer industry. ... Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). ...


Early microcomputer bus systems were essentially a passive backplane connected directly or through buffer amplifiers to the pins of the CPU. 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 interrupted 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 in the Altair. The Commodore 64 was one of the most popular microcomputers of its era, and is the best selling model of home computer of all time. ... A backplane is a circuit board (usually a printed circuit board) that connects several connectors in parallel to 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. ... CPU redirects here. ... CPU redirects here. ... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ... Disk Drive is the afternoon show on CBC Radio Two. ... For other uses, see S-100. ... Altair 8800 Computer with 8 inch floppy disk system The MITS Altair 8800 was a microcomputer design from 1975, based on the Intel 8080 CPU and sold as a mail-order kit through advertisements in Popular Electronics, Radio-Electronics and other hobbyist magazines. ...


In some instances, most notably in the IBM PC, although similar physical architecture is 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. IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ...


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 shares a single clock.


Increasing the speed of the CPU becomes harder, because the speed of all the devices must increase as well. This often led to odd situation where very fast CPUs had to "slow down"[citation needed] in order 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. What is an Embedded System? Electronic devices that incorporate a computer(usually a microprocessor) within their implementation. ...


Such bus systems are also difficult to configure when constructed from common off-the-shelf equipment. Typically each added expansion card requires many jumpers in order to set memory addresses, I/O addresses, interrupt priorities, and interrupt numbers. An expansion card (also expansion board, adapter card or accessory card) in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard to add additional functionality to a computer system. ... Top: jumper block on IDE hard drive with shunt; bottom: assorted shunts In electronics and particularly computing, a jumper is two or more connecting points that can be conveniently shorted together to set up or adjust a printed circuit board, such as a computers motherboard. ...


Second generation

"Second generation" bus systems like NuBus 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, with a bus controller in between. This allowed the CPU to increase in speed without affecting the bus. This also moved much of the burden for moving the data out of the CPU and into the cards and controller, so 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. NuBus 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. ... In computing, a parallel port is an interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. ... Plug and Play is a term used in the computer field to describe a computers ability to have new devices, normally peripherals, added to it without having to restart the computer. ...


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 cards quickly outran even the newer bus systems like PCI, and computers began to include AGP just to drive the video card. By 2004 AGP was outgrown again by high-end video cards and is being replaced with the new PCI Express bus. A video card, also referred to as a graphics accelerator card, display adapter, graphics card, and numerous other terms, is an item of personal computer hardware whose function is to generate and output images to a display. ... This article is about the computer bus type. ... The Accelerated Graphics Port (also called Advanced Graphics Port, often shortened to AGP) is a high-speed point-to-point channel for attaching a graphics card to a computers motherboard, primarily to assist in the acceleration of 3D computer graphics. ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ...


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 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. Scuzzy redirects here. ... ATA cables: 40 wire ribbon cable top, 80 wire ribbon cable bottom Advanced Technology Attachment (ATA), is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. ...


Third generation

"Third generation" buses are now[when?] in the process of coming to market, including HyperTransport and InfiniBand. 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 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. HyperTransport logo HyperTransport (HT), formerly known as Lightning Data Transport (LDT), is a bidirectional serial/parallel high-bandwidth, low-latency point to point link that was introduced on April 2, 2001. ... The panel of an InfiniBand switch InfiniBand is a switched fabric communications link primarily used in high-performance computing. ... A computer network is an interconnection of a group of computers. ...


Buses such as Wishbone have been developed by the open source hardware movement in an attempt to further remove legal/patenting constraints from computer design. The Wishbone Bus is an open source hardware computer bus intended to let the parts of an integrated circuit communicate with each other. ... It has been suggested that this article or section be merged with open 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, 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 serial bus. 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, FireWire, and Serial ATA 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. In computing, a parallel port is an interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. ... A serial bus is a computer bus that sends data bit by bit down one or a few wires. ... An I-button in a plastic fob. ... Timing skew is a problem that can occur on many kinds of computer buses. ... In telecommunication, the term crosstalk (XT) has the following meanings: 1. ... In computing, a double pumped computer bus transfers data on both the rising and falling edges of the clock signal, effectively doubling the data transmission rate without having to deal with the additional problems of timing skew that increasing the number of data lines would introduce. ... USB redirects here. ... The 6-pin and 4-pin FireWire 400 Connectors The alternative ethernet-style cabling used by 1394c FireWire is Apple Inc. ... For other uses of SATA or Sata, see SATA (disambiguation). ... This article needs to be cleaned up to conform to a higher standard of quality. ... Daisy chain A daisy chain, in the most elementary sense, is a garland created from the daisy flower, generally as a childrens game. ...


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 and internal memory). These types of buses are also referred to as a local bus, 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. CPU redirects here. ... Internal memory: In a computer, all of the storage spaces that are accessible by a processor without the use of the computer input-output channels. ... 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. ...


Network connections such as Ethernet are not generally regarded as buses, although the difference is largely conceptual rather than practical. The arrival of technologies such as InfiniBand and HyperTransport is further blurring the boundaries between networks and buses. Even the lines between internal and external are sometimes fuzzy, I²C can be used as both an internal bus, or an external bus (where it is known as ACCESS.bus), and InfiniBand is intended to replace both internal buses like PCI as well as external ones like Fibre Channel. A computer network is an interconnection of a group of computers. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... The panel of an InfiniBand switch InfiniBand is a switched fabric communications link primarily used in high-performance computing. ... HyperTransport logo HyperTransport (HT), formerly known as Lightning Data Transport (LDT), is a bidirectional serial/parallel high-bandwidth, low-latency point to point link that was introduced on April 2, 2001. ... I²C is a multi-master serial computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, or cellphone. ... ACCESS.bus (or A.b) is a peripheral-interconnect computer bus developed by Philips in the early 1990s. ... This article is about the computer bus type. ... Fibre Channel is a gigabit-speed network technology primarily used for storage networking. ...


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.


Bus benefit: any computer can be accessed directly and messages can be sent in a relatively simple and fast way. Disadvantage: needs a scheduler to assign frequencies and priorities to organize the traffic.


See also: Bus network. Image showing bus network layout A bus network Topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. ...


Examples of internal computer buses

Parallel

There are very few or no other articles that link to this one. ... ASUSTeK Computer Incorporated (Asus) (TSE: 2357) (traditional Chinese: ) is a Taiwan-based company that produces motherboards, graphics cards, optical drives, PDAs, notebook computers, servers, networking products, mobile phones, computer cases, computer components and computer cooling systems. ... Socket 7 is a physical and electrical specification for an x86-style CPU socket on a personal computer motherboard. ... Camac Harps (Les Harpes Camac) is a French company that manufactures pedal (concert) harps, lever (folk) harps, and electric pedal and lever harps. ... The Extended Industry Standard Architecture (in practice almost always shortened to EISA and pronounced eee-suh) is a bus standard for IBM compatible computers. ... This article does not cite any references or sources. ... The Low Pin Count bus, or LPC bus, is used on PC-style personal computers to connect low-bandwidth devices to the CPU, such as the boot ROM, the legacy I/O devices (behind a Super I/O chip), and audio controllers. ... Micro Channel architecture (in practice almost always shortened to MCA) was a proprietary 16 or 32-bit parallel computer bus created by IBM in the 1980s for use on their new PS/2 computers. ... Multibus is a computer bus standard used in industrial systems. ... NuBus 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. ... The Intel486[1] brand refers to Intels family of i486 (incl. ... This article is about the computer bus type. ... For other uses, see S-100. ... Altair (α Aql / α Aquilae / Alpha Aquilae / Atair ) is the brightest star in the constellation Aquila and the twelfth brightest star in the nighttime sky, at visual magnitude 0. ... Apple IIc Generally, a microcomputer is a computer with a microprocessor (µP) as its CPU. Another general characteristic of these computers is that they occupy physically small amounts of space. ... SBus is a computer bus system that was used in most SPARC-based computers from Sun Microsystems during the 1990s. ... This article or section does not cite any references or sources. ... 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. ... The Unibus was the earliest of several bus technologies used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts. ... The Q-bus (also known as the LSI-11 Bus) was one of several bus technologies used with PDP and MicroVAX computer systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts. ...

Serial

An I-button in a plastic fob. ... HyperTransport logo HyperTransport (HT), formerly known as Lightning Data Transport (LDT), is a bidirectional serial/parallel high-bandwidth, low-latency point to point link that was introduced on April 2, 2001. ... I²C is a multi-master serial computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, or cellphone. ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ... The Serial Peripheral Interface Bus or SPI (often pronounced es-pē-ī [IPA: ɛs pi aɪ] or spy [IPA: spaɪ]) bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. ... The 6-pin and 4-pin FireWire 400 Connectors The alternative ethernet-style cabling used by 1394c FireWire is Apple Inc. ...

Examples of external computer buses

Parallel

  • Advanced Technology Attachment or ATA (aka PATA, IDE, EIDE, ATAPI, etc.) disk/tape peripheral attachment bus
    (the original ATA is parallel, but see also the recent serial ATA)
  • HIPPI HIgh Performance Parallel Interface
  • IEEE-488 (aka GPIB, General-Purpose Instrumentation Bus, and HPIB, Hewlett-Packard Instrumentation Bus)
  • PC card, 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
  • SCSI Small Computer System Interface, disk/tape peripheral attachment bus

ATA cables: 40 wire ribbon cable top, 80 wire ribbon cable bottom Advanced Technology Attachment (ATA) is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. ... For other uses of SATA or Sata, see SATA (disambiguation). ... HIPPI (HIgh Performance Parallel Interface) is a computer bus for the attachment of high speed storage devices to supercomputers. ... The Hewlett-Packard Instrument Bus (HP-IB), is a short-range digital communications cable standard developed by Hewlett-Packard (HP) in the 1970s for connecting electronic test and measurement devices (e. ... The PCMCIA is the Personal Computer Memory Card International Association, an industry trade association that creates standards for notebook computer peripheral devices. ... Scuzzy redirects here. ...

Serial

Note: USB may also mean upper sideband in radio. ... 2. ... Scuzzy redirects here. ... For other uses of SATA or Sata, see SATA (disambiguation). ... Controller Area Network (CAN or CAN-bus) is a computer network protocol and bus standard designed to allow microcontrollers and devices to communicate with each other and without a host computer. ... RS485 can be used to communicate with remote devices at distances up to 4000ft (1200m) at speeds of up to 100Kbps at this distance. ... The 6-pin and 4-pin FireWire 400 Connectors The alternative ethernet-style cabling used by 1394c FireWire is Apple Inc. ...

Examples of internal/external computer buses

Futurebus (IEEE 896) 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 panel of an InfiniBand switch InfiniBand is a switched fabric communications link primarily used in high-performance computing. ... QuickRing was a gigabit-rate interconnect that combined the functions of a computer bus and a network. ... SCI, for Scalable Coherent Interface, is a high-speed computer bus that supports a variety of topologies, speeds and connection systems. ...

See also

An address bus is (part of) a computer bus, used by CPUs or DMA-capable units for communicating the physical addresses of computer memory elements/locations that the requesting unit wants to access (read/write). ... Bus contention is an undesirable state of the bus of a computer, in which more than one memory mapped device or the CPU is attempting to place output values onto the bus at once. ... A control bus is sabilas bum has cheese crust (part of) a computer bus, used by CPUs for communicating with other devices within the computer. ... A typical north/southbridge layout In personal computers, the Front Side Bus (FSB) is the data transfer bus that carries information between the CPU and the northbridge of the Motherboard. ... Network-on-a-chip (NoC) is a new approach to System-on-a-chip (SoC) design. ... This is a list of device bandwidths: the channel capacity (or, more informally, bandwidth) of some computer devices employing methods of data transport is quantified in units of kilobits per second (kbit/s), megabits per second (Mbit/s), or gigabits per second (Gbit/s) as appropriate. ...

External links

The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ...

  Results from FactBites:
 
Bus (computer) - MSN Encarta (591 words)
In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers.
Bus (computer), in computer science, a set of wires used for data transfer among the components of a computer system.
Because the bus is integral to internal data transfer and yet computer users often need to add extra components to the system, most microcomputer buses allow for expansion through one or more expansion slots (connectors for add-on circuit boards).
Method and system for avoiding live lock conditions on a computer bus by insuring that the first retired bus master is ... (6177 words)
The bus controller may prevent execution of the transaction request from the other bus masters by transmitting retry commands to all bus masters that submit transaction requests after the transaction request from the first bus master is received and before the first bus master re-submits the transaction request.
The computer system of claim 14 wherein the bus controller includes a bus interface and a buffer associated with the target device, the bus interface determining whether the target device is available to execute the first transaction request by determining whether the buffer is in a state that enables execution of the first transaction request.
Bus master 1 re-submits its second read transaction request and the PCI target interface processes it normally because the write buffer is still empty and the bus master 1 no longer has an ineligible flag associated with it.
  More results at FactBites »

 
 

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