Bus - Revision history

Jnc: Avoid redir

2024-12-21T14:02:12Z

Avoid redir

Jnc: arg syntax err

2019-09-05T03:09:48Z

arg syntax err

Jnc: New wiki template, proper cat

2019-09-05T03:06:31Z

New wiki template, proper cat

Jnc: Bah, another one

2018-11-17T17:29:38Z

Bah, another one

Jnc: link to single form

2018-11-17T16:40:37Z

link to single form

Jnc: rm year links

2017-11-07T16:33:46Z

rm year links

Jnc: rm dup linkage

2017-09-21T19:28:51Z

rm dup linkage

Jnc: avoid redir

2017-09-21T19:27:06Z

avoid redir

Tor: Make 'S-100 bus' link to the S-100 page.

2013-01-09T11:48:36Z

Make 'S-100 bus' link to the S-100 page.

Archivist: /* Parallel */

2007-05-22T12:52:00Z

‎Parallel

@@ Line 79: / Line 79: @@
 * [[SBus]] or IEEE 1496
 * [[VESA Local Bus]] or VLB or VL-bus
-* [[VME]], the VERSAmodule Eurocard bus
+* [[VMEbus]], the VERSAmodule Eurocard bus
 * STD Bus for 8- and 16-bit microprocessor systems

@@ Line 114: / Line 114: @@
 * Chip Weems' [http://www.cs.umass.edu/~weems/CmpSci635/635lecture12.html Lecture 12: Buses]
-{{Wikipedia|Bus (computing)}}
+{{Wikipedia|Bus_(computing)}}
 [[Category: Hardware Basics]]

@@ Line 1: / Line 1: @@
-{{wp-orig}}
+In computer [[architecture]], a '''bus''' is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by [[device driver]] software. Unlike a [[Point-to-point link|point-to-point connection]], a bus can logically connect several [[peripheral]]s over the same set of wires. Each bus defines its set of [[connector]]s to physically plug devices, cards or cables together.
 Early computer buses were literally parallel [[electrical bus]]es 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 [[Universal Serial Bus|USB]].
@@ Line 115: / Line 113: @@
 == External links ==
 * Chip Weems' [http://www.cs.umass.edu/~weems/CmpSci635/635lecture12.html Lecture 12: Buses]
-[[Category:Computer buses|*Computer bus]]
+{{Wikipedia|Bus (computing)}}

@@ Line 6: / Line 6: @@
 ===First generation===
-Early [[computer]] buses were bundles of wire that attached [[Computer storage|memory]] and peripherals.  They were named after [[Electrical bus|electrical buses]], or busbars.  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.
+Early [[computer]] buses were bundles of wire that attached [[Computer storage|memory]] and peripherals. They were named after electrical buses, or busbars.  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]]s.  Early computers performed [[Input/output|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 lost 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.
@@ Line 78: / Line 78: @@
 * [[OPTi local bus]] used on early [[Intel 80486]] motherboards.
 * [[Peripheral Component Interconnect]] or PCI
-* [[S100]] bus or IEEE 696, used in the [[Altair]] and similar [[microcomputers]]
+* [[S100]] bus or IEEE 696, used in the [[Altair]] and similar [[microcomputer]]s
 * [[SBus]] or IEEE 1496
 * [[VESA Local Bus]] or VLB or VL-bus

@@ Line 18: / Line 18: @@
 Early [[microcomputer]] bus systems were essentially a passive [[backplane]] connected to the pins of the [[Central Processing Unit|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. In some instances, such as the [[IBM PC]], instructions still generated signals at the CPU that could be used to implement a true I/O bus.
-In many microcontrollers and [[embedded systems]], an I/O bus still does not exist.  Communication is controlled by the CPU, which reads and writes data from the devices as if they are blocks of memory (in most cases), all timed by a central clock controlling the speed of the CPU. Devices ask for service by signalling on other CPU pins, typically using some form of [[interrupt]].
+In many microcontrollers and [[embedded system]]s, an I/O bus still does not exist.  Communication is controlled by the CPU, which reads and writes data from the devices as if they are blocks of memory (in most cases), all timed by a central clock controlling the speed of the CPU. Devices ask for service by signalling on other CPU pins, typically using some form of [[interrupt]].
 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 that corresponded to the disk drive. Almost all early computers were built in this fashion, starting with the [[S-100|S-100 bus]] in the [[Altair 8800|Altair]], and continuing through the [[IBM PC]] in the 1980s.

@@ Line 20: / Line 20: @@
 In many microcontrollers and [[embedded systems]], an I/O bus still does not exist.  Communication is controlled by the CPU, which reads and writes data from the devices as if they are blocks of memory (in most cases), all timed by a central clock controlling the speed of the CPU. Devices ask for service by signalling on other CPU pins, typically using some form of [[interrupt]].
-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 that corresponded to the disk drive. Almost all early computers were built in this fashion, starting with the [[S-100|S-100 bus]] in the [[Altair 8800|Altair]], and continuing through the [[IBM PC]] in the [[1980s]].
+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 that corresponded to the disk drive. Almost all early computers were built in this fashion, starting with the [[S-100|S-100 bus]] in the [[Altair 8800|Altair]], and continuing through the [[IBM PC]] in the 1980s.
 These simple bus systems had a serious drawback for general-purpose computers.  All the equipment on the bus has to talk at the same speed, and thus shares a single clock.
@@ Line 35: / Line 35: @@
 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]]s quickly outran even the newer bus systems like '''[[Peripheral Component Interconnect|PCI]]''', and computers began to include '''[[Accelerated Graphics Port|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.
-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 '''[[Integrated Drive Electronics|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.
+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 '''[[Integrated Drive Electronics|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.
 A useful differentiation then became popular, the concept of the '''local bus''' as opposed to '''external bus'''. The former referred to bus systems that were designed to be used with internal devices, such as graphics cards, and the latter to buses designed to add external devices such as [[image scanner|scanner]]s. Note, though, that "local" also referred to the greater proximity to the processor of VL-Bus and PCI than ISA. IDE is an external bus in terms of how it is used, but is almost always found inside the machine.

@@ Line 18: / Line 18: @@
 Early [[microcomputer]] bus systems were essentially a passive [[backplane]] connected to the pins of the [[Central Processing Unit|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. In some instances, such as the [[IBM PC]], instructions still generated signals at the CPU that could be used to implement a true I/O bus.
-In many microcontrollers and [[embedded systems]], an I/O bus still does not exist.  Communication is controlled by the [[Central processing unit|CPU]], which reads and writes data from the devices as if they are blocks of memory (in most cases), all timed by a central clock controlling the speed of the CPU. Devices ask for service by signalling on other CPU pins, typically using some form of [[interrupt]].
+In many microcontrollers and [[embedded systems]], an I/O bus still does not exist.  Communication is controlled by the CPU, which reads and writes data from the devices as if they are blocks of memory (in most cases), all timed by a central clock controlling the speed of the CPU. Devices ask for service by signalling on other CPU pins, typically using some form of [[interrupt]].
 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 that corresponded to the disk drive. Almost all early computers were built in this fashion, starting with the [[S-100|S-100 bus]] in the [[Altair 8800|Altair]], and continuing through the [[IBM PC]] in the [[1980s]].
@@ Line 49: / Line 49: @@
 Buses can be [[parallel communications|parallel buses]], which carry data words striped across multiple wires, or [[serial bus]]es, 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 two used in the [[I²C]] serial bus. As data rates increase, the problems of [[timing skew]] and [[crosstalk]] across parallel buses become more and more difficult to circumvent. One partial solution to this problem has been to [[double pumped|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.  [[Universal Serial Bus|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.
-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 [[Central processing unit|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.
+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 [[main 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.
 [[computer network|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 [[Peripheral Component Interconnect|PCI]] as well as external ones like [[Fibre Channel]].

@@ Line 16: / Line 16: @@
 [[Digital Equipment Corporation|DEC]] noted that having two buses seemed wasteful and expensive for small, mass-produced computers, and mapped peripherals into the memory bus, so that the devices appeared to be memory locations.  At the time, this was a very daring design.  Cynics predicted failure.
-Early [[microcomputer]] bus systems were essentially a passive [[backplane]] connected to the pins of the [[Central processing unit|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. In some instances, such as the [[IBM PC]], instructions still generated signals at the CPU that could be used to implement a true I/O bus.
+Early [[microcomputer]] bus systems were essentially a passive [[backplane]] connected to the pins of the [[Central Processing Unit|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. In some instances, such as the [[IBM PC]], instructions still generated signals at the CPU that could be used to implement a true I/O bus.
 In many microcontrollers and [[embedded systems]], an I/O bus still does not exist.  Communication is controlled by the [[Central processing unit|CPU]], which reads and writes data from the devices as if they are blocks of memory (in most cases), all timed by a central clock controlling the speed of the CPU. Devices ask for service by signalling on other CPU pins, typically using some form of [[interrupt]].