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53-462: It consisted of up to three customized DSP boards that could be plugged into the expansion bus on a NeXT Computer (a "cube"). The ISPW could then run a customized real-time audio processing server on the hardware boards controlled by a client application on the NeXT. Each ISPW card had two Intel i860 microprocessors (running at 80 MFLOPS ). An additional card with eight channels of audio I/O

106-453: A busbar (also bus bar ) is a metallic strip or bar, typically housed inside switchgear , panel boards , and busway enclosures for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low-voltage equipment in battery banks . They are generally uninsulated, and have sufficient stiffness to be supported in air by insulated pillars. These features allow sufficient cooling of

159-730: A bidirectional data bus, re-using the same wires for input and output at different times. Some processors use a dedicated wire for each bit of the address bus, data bus, and the control bus. For example, the 64-pin STEbus is composed of 8 physical wires dedicated to the 8-bit data bus, 20 physical wires dedicated to the 20-bit address bus, 21 physical wires dedicated to the control bus, and 15 physical wires dedicated to various power buses. Bus multiplexing requires fewer wires, which reduces costs in many early microprocessors and DRAM chips. One common multiplexing scheme, address multiplexing , has already been mentioned. Another multiplexing scheme re-uses

212-726: 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. "Third generation" buses have been emerging into the market since about 2001, 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

265-428: A metal earthed enclosure or by elevation out of normal reach. Insulated bus bars are used in busways listed to UL 857 standards. Power neutral busbars may also be insulated because it is not guaranteed that the potential between power neutral and safety grounding is always zero. Earthing (safety grounding) busbars are typically bare and bolted directly onto any metal chassis of their enclosure. They may be enclosed in

318-442: A metal housing, in the form of a bus duct or busway, segregated-phase bus, or isolated-phase bus . Busbars may be connected to each other and to electrical apparatus by bolting, clamping or welding. Joints between high-current bus sections often have precisely machined matching surfaces that are silver-plated to reduce contact resistance . At extra high voltages (more than 300 kV) in outdoor buses, corona discharge around

371-515: 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 read and wrote data from the devices as if they are blocks of memory, using the same instructions, all timed by a central clock controlling

424-527: A sandwich of thin conductor layers, were developed. They require a structural frame or cabinet for their installation. Distribution boards split the electrical supply into separate circuits at one location. Busways, or bus ducts, are long busbars with protective covers. Rather than branching from the main supply at one location, they allow new circuits to branch off anywhere along the busway. A busbar may be either supported on insulators, or wrapped in insulation. They are protected from accidental contact either by

477-511: A second set of pins similar to those for communicating with memory—but able to operate with different speeds and protocols—to ensure that peripherals do not slow overall system performance. CPUs can also feature smart controllers to place the data directly in memory, a concept known as direct memory access . Low-performance bus systems have also been developed, such as the Universal Serial Bus (USB). Given technological changes,

530-506: 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. The transition from parallel to serial buses was allowed by Moore's law which allowed for the incorporation of SerDes in integrated circuits which are used in computers. Network connections such as Ethernet are not generally regarded as buses, although

583-449: A single source LRI/LRU or, as with ARINC 629, MIL-STD-1553B, and STANAG 3910, be duplex , allow all the connected LRI/LRUs to act, at different times ( half duplex ), as transmitters and receivers of data. The frequency or the speed of a bus is measured in Hz such as MHz and determines how many clock cycles there are per second; there can be one or more data transfers per clock cycle. If there

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636-587: A solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoor electrical switchyards . A busbar must be sufficiently rigid to support its own weight, and forces imposed by mechanical vibration and possibly earthquakes , as well as accumulated precipitation in outdoor exposures. In addition, thermal expansion from temperature changes induced by ohmic heating and ambient temperature variations, and magnetic forces induced by large currents, must be considered. To address these concerns, flexible bus bars, typically

689-433: A unified system bus . In this case, a single mechanical and electrical system can be used to connect together many of the system components, or in some cases, all of them. Later computer programs began to share memory common to several CPUs. Access to this memory bus had to be prioritized, as well. The simple way to prioritize interrupts or bus access was with a daisy chain . In this case signals will naturally flow through

742-473: Is a stub . You can help Misplaced Pages by expanding it . Computer bus In computer architecture , a bus (historically also called data highway or databus ) is a communication system that transfers data between components inside a computer , or between computers. This expression covers all related hardware components (wire, optical fiber , etc.) and software , including communication protocols . In most traditional computer architectures ,

795-412: Is a single transfer per clock cycle it is known as Single Data Rate (SDR), and if there are two transfers per clock cycle it is known as Double Data Rate (DDR) although the use of signalling other than SDR is uncommon outside of RAM. An example of this is PCIe which uses SDR. Within each data transfer there can be multiple bits of data. This is described as the width of a bus which is the number of bits

848-540: Is an open standard interconnect for high-speed CPU -to-device and CPU-to-memory, designed to accelerate next-generation data center performance. Many field buses are serial data buses (not to be confused with the parallel "data bus" section of a system bus or expansion card ), several of which use the RS-485 electrical characteristics and then specify their own protocol and connector: Other serial buses include: Busbar In electric power distribution ,

901-475: Is provided by the bus‍—‌is not the case in many avionic systems , where data connections such as ARINC 429 , ARINC 629 , MIL-STD-1553B (STANAG 3838), and EFABus ( STANAG 3910 ) are commonly referred to as “data buses” or, sometimes, "databuses". Such avionic data buses are usually characterized by having several equipments or Line Replaceable Items/Units (LRI/LRUs) connected to a common, shared media . They may, as with ARINC 429, be simplex , i.e. have

954-424: Is sent on the data bus). The width of the address bus determines the amount of memory a system can address. For example, a system with a 32-bit address bus can address 2 (4,294,967,296) memory locations. If each memory location holds one byte, the addressable memory space is 4 GB. Early processors used a wire for each bit of the address width. For example, a 16-bit address bus had 16 physical wires making up

1007-491: Is the case, for instance, with the VESA Local Bus which lacks the two least significant bits, limiting this bus to aligned 32-bit transfers. Historically, there were also some examples of computers which were only able to address words -- word machines . The memory bus is the bus which connects the main memory to the memory controller in computer systems . Originally, general-purpose buses like VMEbus and

1060-473: The IBM PC , 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 had to talk at

1113-889: The S-100 bus were used, but to reduce latency , modern memory buses are designed to connect directly to DRAM chips, and thus are designed by chip standards bodies such as JEDEC . Examples are the various generations of SDRAM , and serial point-to-point buses like SLDRAM and RDRAM . An exception is the Fully Buffered DIMM which, despite being carefully designed to minimize the effect, has been criticized for its higher latency. 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

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1166-621: The electrochemical cells that produce aluminium from molten salts . Busbars are produced in a variety of shapes, including flat strips, solid bars and rods, and are typically composed of copper , brass or aluminium as solid or hollow tubes. Some of these shapes allow heat to dissipate more efficiently due to their high surface area to cross-sectional area ratio. The skin effect makes 50–60 Hz AC busbars more than about 8 millimetres (0.31 in) thickness inefficient, so hollow or flat shapes are prevalent in higher-current applications. A hollow section also has higher stiffness than

1219-399: The CPU and main memory tend to be tightly coupled, with the internal bus connecting the two being known as the system bus . In systems that include a cache , CPUs use high-performance system buses that operate at speeds greater than memory to communicate with memory. The internal bus (also known as the internal data bus, memory bus or system bus ) connects internal components of a computer to

1272-472: The IEEE "Superbus" study group, the open microprocessor initiative (OMI), the open microsystems initiative (OMI), the "Gang of Nine" that developed EISA , etc. Early computer buses were bundles of wire that attached computer memory and peripherals. Anecdotally termed the " digit trunk " in the early Australian CSIRAC computer, they were named after electrical power buses, or busbars . Almost always, there

1325-596: The ISPW was called FTS ("Faster Than Sound"). The main NeXT client application was a graphical program called Max , developed by Miller Puckette . A commercial version of Max (without the FTS server) was licensed by IRCAM to Opcode Systems (and, later, Cycling '74 ). Max/FTS eventually migrated to a software-only application for SGI and DEC Alpha computers. It is the direct predecessor to jMax . See also Pd . This microcomputer - or microprocessor -related article

1378-549: The address bus pins as the data bus pins, an approach used by conventional PCI and the 8086 . The various "serial buses" can be seen as the ultimate limit of multiplexing, sending each of the address bits and each of the data bits, one at a time, through a single pin (or a single differential pair). Over time, several groups of people worked on various computer bus standards, including the IEEE Bus Architecture Standards Committee (BASC),

1431-489: The bits themselves, and allows for an increase in data transfer speed without increasing the frequency of the bus. The effective or real data transfer speed/rate may be lower due to the use of encoding that also allows for error correction such as 128/130b (b for bit) encoding. The data transfer speed is also known as the bandwidth. The simplest system bus has completely separate input data lines, output data lines, and address lines. To reduce cost, most microcomputers have

1484-493: The bus can transfer per clock cycle and can be synonymous with the number of physical electrical conductors the bus has if each conductor transfers one bit at a time. The data rate in bits per second can be obtained by multiplying the number of bits per clock cycle times the frequency times the number of transfers per clock cycle. Alternatively a bus such as PCIe can use modulation or encoding such as PAM4 which groups 2 bits into symbols which are then transferred instead of

1537-409: The bus had to talk at the same speed. While the CPU was now isolated and could increase speed, 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 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

1590-519: The bus in physical or logical order, eliminating the need for complex scheduling. Digital Equipment Corporation (DEC) further reduced cost for mass-produced minicomputers , and mapped peripherals into the memory bus, so that the input and output devices appeared to be memory locations. This was implemented in the Unibus of the PDP-11 around 1969. Early microcomputer bus systems were essentially

1643-626: The bus supplied power, but often use a separate power source. This distinction is exemplified by a telephone system with a connected modem , where the RJ11 connection and associated modulated signalling scheme is not considered a bus, and is analogous to an Ethernet connection. A phone line connection scheme is not considered to be a bus with respect to signals, but the Central Office uses buses with cross-bar switches for connections between phones. However, this distinction‍—‌that power

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1696-461: The bus. As the buses became wider and lengthier, this approach became expensive in terms of the number of chip pins and board traces. Beginning with the Mostek 4096 DRAM , address multiplexing implemented with multiplexers became common. In a multiplexed address scheme, the address is sent in two equal parts on alternate bus cycles. This halves the number of address bus signals required to connect to

1749-431: 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

1802-426: The classical terms "system", "expansion" and "peripheral" no longer have the same connotations. Other common categorization systems are based on the bus's primary role, connecting devices internally or externally. However, many common modern bus systems can be used for both. SATA and the associated eSATA are one example of a system that would formerly be described as internal, while certain automotive applications use

1855-491: 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

1908-501: The conductors, and the ability to tap in at various points without creating a new joint. The busbar's material composition and cross-sectional size determine the maximum current it can safely carry. Busbars can have a cross-sectional area of as little as 10 square millimetres (0.016 sq in), but electrical substations may use metal tubes 50 millimetres (2.0 in) in diameter or more as busbars. Aluminium smelters use very large busbars to carry tens of thousands of amperes to

1961-489: The difference is largely conceptual rather than practical. An attribute generally used to characterize a bus is that power is provided by the bus for the connected hardware. This emphasizes the busbar origins of bus architecture as supplying switched or distributed power. This excludes, as buses, schemes such as serial RS-232 , parallel Centronics , IEEE 1284 interfaces and Ethernet, since these devices also needed separate power supplies. Universal Serial Bus devices may use

2014-400: The first half of the memory address or the second half. Accessing an individual byte frequently requires reading or writing the full bus width (a word ) at once. In these instances the least significant bits of the address bus may not even be implemented - it is instead the responsibility of the controlling device to isolate the individual byte required from the complete word transmitted. This

2067-635: The input and output of a given bus. IBM introduced these on the IBM 709 in 1958, and they became a common feature of their platforms. Other high-performance vendors like Control Data Corporation implemented similar designs. Generally, the channel controllers would do their best to run all of the bus operations internally, moving data when the CPU was known to be busy elsewhere if possible, and only using interrupts when necessary. This greatly reduced CPU load, and provided better overall system performance. To provide modularity, memory and I/O buses can be combined into

2120-452: The memory. For example, a 32-bit address bus can be implemented by using 16 lines and sending the first half of the memory address, immediately followed by the second half memory address. Typically two additional pins in the control bus – row-address strobe (RAS) and column-address strobe (CAS) – are used to tell the DRAM whether the address bus is currently sending

2173-446: The minimum of one used in 1-Wire and UNI/O . 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 be operated at higher overall data rates than a parallel bus, despite having fewer electrical connections, because

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2226-465: The mother board. Local buses connect the CPU and memory to the expansion bus , which in turn connects the computer to peripherals. Bus systems such as the SATA ports in modern computers support multiple peripherals, allowing multiple hard drives to be connected without an expansion card . In systems that have a similar architecture to multicomputers , but which communicate by buses instead of networks,

2279-401: 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 other peripherals and has been replaced by 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

2332-502: The peripheral bus, which includes bus systems like PCI. Early computer buses were parallel electrical wires with multiple hardware connections, but the term is now used for any physical arrangement that provides the same logical function as a parallel electrical busbar . 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. Many modern CPUs also feature

2385-441: The primarily external IEEE 1394 in a fashion more similar to a system bus. Other examples, like InfiniBand and I²C were designed from the start to be used both internally and externally. An address bus is a bus that is used to specify a physical address . When a processor or DMA -enabled device needs to read or write to a memory location, it specifies that memory location on the address bus (the value to be read or written

2438-484: 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. High-end systems introduced the idea of channel controllers , which were essentially small computers dedicated to handling

2491-420: 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 , or work at a slower clock frequency temporarily, to talk to other devices in the computer. While acceptable in embedded systems , this problem

2544-522: 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 8800 computer system. In some instances, most notably in

2597-399: The system bus is known as a front-side bus . In such systems, the expansion bus may not share any architecture with their host CPUs, instead supporting many different CPUs, as is the case with PCI . While the term " peripheral bus " is sometimes used to refer to all other buses apart from the system bus, the "expansion bus" has also been used to describe a third category of buses separate from

2650-522: 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. Buses such as Wishbone have been developed by the open source hardware movement in an attempt to further remove legal and patent constraints from computer design. The Compute Express Link (CXL)

2703-530: Was also available for multi-channel sound recording and playback. A three-board ISPW provided what was at the time unsurpassed signal processing and audio synthesis power on a single workstation. A single ISPW card cost approximately $ 12,000US (not including the computer), which made it prohibitively expensive outside of research institutes and universities. [REDACTED] And the I860 board : [REDACTED] The main server software developed by IRCAM for

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2756-441: 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 requires many jumpers in order to set memory addresses, I/O addresses, interrupt priorities, and interrupt numbers. "Second generation" bus systems like NuBus addressed some of these problems. They typically separated

2809-402: Was one bus for memory, and one or more separate buses for peripherals. These were accessed by separate instructions, with completely different timings and protocols. One of the first complications was the use of interrupts . Early computer programs 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

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