1.
Serial port
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In computing, a serial port is a serial communication interface through which information transfers in or out one bit at a time. Throughout most of the history of computers, data was transferred through serial ports to devices such as modems, terminals. Modern computers without serial ports may require serial-to-USB converters to allow compatibility with RS-232 serial devices, serial ports are still used in applications such as industrial automation systems, scientific instruments, point of sale systems and some industrial and consumer products. Server computers may use a port as a control console for diagnostics. Network equipment often use serial console for configuration, serial ports are still used in these areas as they are simple, cheap and their console functions are highly standardized and widespread. A serial port requires very little supporting software from the host system, some computers, such as the IBM PC, use an integrated circuit called a UART. This IC converts characters to and from asynchronous serial form, implementing the timing and framing of data in hardware, very low-cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the bit-banging technique. Early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS-232, low-cost processors now allow higher-speed, but more complex, serial communication standards such as USB and FireWire to replace RS-232. These make it possible to connect devices that would not have operated feasibly over slower serial connections, such as storage, sound. Many personal computer motherboards still have at least one serial port, small-form-factor systems and laptops may omit RS-232 connector ports to conserve space, but the electronics are still there. RS-232 has been standard for so long that the circuits needed to control a serial port became very cheap and often exist on a single chip, sometimes also with circuitry for a parallel port. The individual signals on a serial port are unidirectional and when connecting two devices the outputs of one device must be connected to the inputs of the other, devices are divided into two categories data terminal equipment and data circuit-terminating equipment. A line that is an output on a DTE device is an input on a DCE device and vice versa so a DCE device can be connected to a DTE device with a straight wired cable, conventionally, computers and terminals are DTE while modems and peripherals are DCE. If it is necessary to connect two DTE devices a cross-over null modem, in the form of either an adapter or a cable, generally, serial port connectors are gendered, only allowing connectors to mate with a connector of the opposite gender. With D-subminiature connectors, the male connectors have protruding pins, either type of connector can be mounted on equipment or a panel, or terminate a cable. Connectors mounted on DTE are likely to be male, and those mounted on DCE are likely to be female, however, this is far from universal, for instance, most serial printers have a female DB25 connector, but they are DTEs. The desire to supply serial interface cards with two ports required that IBM reduce the size of the connector to fit onto a single card back panel, a DE-9 connector also fits onto a card with a second DB-25 connector. Starting around the time of the introduction of the IBM PC-AT, serial ports were built with a 9-pin connector to save cost
2.
PC compatible
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IBM PC compatible computers are those similar to the original IBM PC, XT, and AT, able to run the same software and support the same expansion cards as those. Such computers used to be referred to as PC clones, or IBM clones, Columbia Data Products built the first clone of the IBM personal computer by a clean room implementation of its BIOS. Early IBM PC compatibles used the computer bus as the original PC. The IBM AT compatible bus was named the Industry Standard Architecture bus by manufacturers of compatible computers. The term IBM PC compatible is now a historical description only, only the Apple Macintosh classic Mac OS and macOS kept significant market share without compatibility with the IBM personal computer, so consumers are typically identified as being a PC or Mac user. IBM decided in 1980 to market a low-cost single-user computer as quickly as possible in response to Apple Computers success in the microcomputer market. On 12 August 1981, the first IBM PC went on sale, there were three operating systems available for it. The least expensive and most popular was PC DOS made by Microsoft, in a crucial concession, IBMs agreement allowed Microsoft to sell its own version, MS-DOS, for non-IBM computers. The only component of the original PC architecture exclusive to IBM was the BIOS and this software would run on any machine using MS-DOS or PC-DOS. Software that directly addressed the hardware instead of making standard calls was faster, however, software addressing IBM PC hardware in this way would not run on MS-DOS machines with different hardware. The 808x computer marketplace rapidly excluded all machines which were not hardware-, the 640 KB barrier on conventional system memory available to MS-DOS is a legacy of that period, other non-clone machines, while subject to a limit, could exceed 640 kB. Rumors of lookalike, compatible computers, created without IBMs approval, by June 1983 PC Magazine defined PC clone as a computer accommodate the user who takes a disk home from an IBM PC, walks across the room, and plugs it into the foreign machine. Because of a shortage of IBM PCs that year, many customers purchased clones instead, Columbia Data Products produced the first computer more or less compatible to the IBM PC standard during June 1982, soon followed by Eagle Computer. Compaq announced its first IBM PC compatible in November 1982, the Compaq Portable, the Compaq was the first sewing machine-sized portable computer that was essentially 100% PC-compatible. The company could not copy the BIOS directly as a result of the decision in Apple v. Franklin. Each computer would have its own Original Equipment Manufacturer version of MS-DOS, any software written for MS-DOS would operate on any MS-DOS computer, despite variations in hardware design. This expectation seemed reasonable in the marketplace of the time. Until then Microsoft was based primarily on computer languages such as BASIC, the established small system operating software was CP/M from Digital Research which was in use both at the hobbyist level and by the more professional of those using microcomputers
3.
Computer
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A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically. The ability of computers to follow a sequence of operations, called a program, such computers are used as control systems for a very wide variety of industrial and consumer devices. The Internet is run on computers and it millions of other computers. Since ancient times, simple manual devices like the abacus aided people in doing calculations, early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century, the first digital electronic calculating machines were developed during World War II. The speed, power, and versatility of computers has increased continuously and dramatically since then, conventionally, a modern computer consists of at least one processing element, typically a central processing unit, and some form of memory. The processing element carries out arithmetic and logical operations, and a sequencing, peripheral devices include input devices, output devices, and input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and this usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century, from the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations. The Online Etymology Dictionary gives the first attested use of computer in the 1640s, one who calculates, the Online Etymology Dictionary states that the use of the term to mean calculating machine is from 1897. The Online Etymology Dictionary indicates that the use of the term. 1945 under this name, theoretical from 1937, as Turing machine, devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick, later record keeping aids throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example, the abacus was initially used for arithmetic tasks. The Roman abacus was developed from used in Babylonia as early as 2400 BC. Since then, many forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, the Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions and it was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to circa 100 BC
4.
Bluetooth
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Bluetooth is a wireless technology standard for exchanging data over short distances from fixed and mobile devices, and building personal area networks. Invented by telecom vendor Ericsson in 1994, it was conceived as a wireless alternative to RS-232 data cables. It can connect up to seven devices, overcoming problems that older technologies had when attempting to connect to each other. Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 30,000 member companies in the areas of telecommunication, computing, networking, the IEEE standardized Bluetooth as IEEE802.15.1, but no longer maintains the standard. The Bluetooth SIG oversees development of the specification, manages the qualification program, a manufacturer must meet Bluetooth SIG standards to market it as a Bluetooth device. A network of patents apply to the technology, which are licensed to individual qualifying devices, the development of the short-link radio technology, later named Bluetooth, was initiated in 1989 by Nils Rydbeck, CTO at Ericsson Mobile in Lund, Sweden, and by Johan Ullman. The purpose was to develop wireless headsets, according to two inventions by Johan Ullman, SE 8902098-6, issued 1989-06-12 and SE9202239, issued 1992-07-24, Nils Rydbeck tasked Tord Wingren with specifying and Jaap Haartsen and Sven Mattisson with developing. Both were working for Ericsson in Lund, the specification is based on frequency-hopping spread spectrum technology. The idea of this name was proposed in 1997 by Jim Kardach who developed a system that would allow mobile phones to communicate with computers, at the time of this proposal he was reading Frans G. Bengtssons historical novel The Long Ships about Vikings and King Harald Bluetooth. The implication is that Bluetooth does the same with communications protocols, the Bluetooth logo is a bind rune merging the Younger Futhark runes and, Haralds initials. Bluetooth operates at frequencies between 2402 and 2480 MHz, or 2400 and 2483.5 MHz including guard bands 2 MHz wide at the end and 3.5 MHz wide at the top. This is in the globally unlicensed Industrial, Scientific and Medical 2.4 GHz short-range radio frequency band, Bluetooth uses a radio technology called frequency-hopping spread spectrum. Bluetooth divides transmitted data into packets, and transmits each packet on one of 79 designated Bluetooth channels, each channel has a bandwidth of 1 MHz. It usually performs 800 hops per second, with Adaptive Frequency-Hopping enabled, Bluetooth low energy uses 2 MHz spacing, which accommodates 40 channels. Originally, Gaussian frequency-shift keying modulation was the modulation scheme available. Since the introduction of Bluetooth 2. 0+EDR, π/4-DQPSK and 8DPSK modulation may also be used between compatible devices, devices functioning with GFSK are said to be operating in basic rate mode where an instantaneous data rate of 1 Mbit/s is possible. The term Enhanced Data Rate is used to describe π/4-DPSK and 8DPSK schemes, the combination of these modes in Bluetooth radio technology is classified as a BR/EDR radio. Bluetooth is a protocol with a master-slave structure
5.
USB
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It is currently developed by the USB Implementers Forum. USB was designed to standardize the connection of peripherals to personal computers. It has become commonplace on other devices, such as smartphones, PDAs, USB has effectively replaced a variety of earlier interfaces, such as serial ports and parallel ports, as well as separate power chargers for portable devices. Also, there are 5 modes of USB data transfer, in order of increasing bandwidth, Low Speed, Full Speed, High Speed, SuperSpeed, USB devices have some choice of implemented modes, and USB version is not a reliable statement of implemented modes. Modes are identified by their names and icons, and the specifications suggests that plugs, unlike other data buses, USB connections are directed, with both upstream and downstream ports emanating from a single host. This applies to power, with only downstream facing ports providing power. Thus, USB cables have different ends, A and B, therefore, in general, each different format requires four different connectors, a plug and receptacle for each of the A and B ends. USB cables have the plugs, and the corresponding receptacles are on the computers or electronic devices, in common practice, the A end is usually the standard format, and the B side varies over standard, mini, and micro. The mini and micro formats also provide for USB On-The-Go with a hermaphroditic AB receptacle, the micro format is the most durable from the point of view of designed insertion lifetime. The standard and mini connectors have a lifetime of 1,500 insertion-removal cycles. Likewise, the component of the retention mechanism, parts that provide required gripping force, were also moved into plugs on the cable side. A group of seven companies began the development of USB in 1994, Compaq, DEC, IBM, Intel, Microsoft, NEC, a team including Ajay Bhatt worked on the standard at Intel, the first integrated circuits supporting USB were produced by Intel in 1995. The original USB1.0 specification, which was introduced in January 1996, Microsoft Windows 95, OSR2.1 provided OEM support for the devices. The first widely used version of USB was 1.1, the 12 Mbit/s data rate was intended for higher-speed devices such as disk drives, and the lower 1.5 Mbit/s rate for low data rate devices such as joysticks. Apple Inc. s iMac was the first mainstream product with USB, following Apples design decision to remove all legacy ports from the iMac, many PC manufacturers began building legacy-free PCs, which led to the broader PC market using USB as a standard. The USB2.0 specification was released in April 2000 and was ratified by the USB Implementers Forum at the end of 2001.1 specification, the USB3.0 specification was published on 12 November 2008. Its main goals were to increase the transfer rate, decrease power consumption, increase power output. USB3.0 includes a new, higher speed bus called SuperSpeed in parallel with the USB2.0 bus, for this reason, the new version is also called SuperSpeed
6.
Pin header
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A pin header is a form of electrical connector. The distance between pins is commonly referred as pitch in the electronic community, in the past, a pin header was known as a Berg connector, but the term fell out of favor because pin headers are manufactured by many companies. Pin headers are often associated with ribbon cable connectors, pin headers often also function as recipients for jumpers, the most common jumper spacing is 2.54 millimetres, though 2.0 millimetres is sometimes used in smaller products. Pin header connectors are thus male connectors and are used inside equipment. Normally pin headers are pin through hole devices, but surface-mount technology versions of one, in the latter case the solder sides of the pins are simply bent on a 90 degree angle so as to be soldered to a solder plane. On single row pin headers the pins are bent alternating to one side or the other, if pin headers are optional, the PTH variant is often chosen for ease of manual assembly. Pin headers can be straight or angled. The latter form is used to connect two boards together. Pin headers are cost-effective due to their simplicity, headers are often sold as long strips which can easily be broken off to the right number of pins. Pin headers with a plastic guide box around them are known as box headers or shrouded headers and are only used in combination with insulation-displacement connectors for ribbon cables. A notch in the guide box normally prevents placing the connector the wrong way around, some systems polarize or key the pin header connection with something that fills and blocks one of the holes in the sockets. One pin of the pin header hits that obstruction and prevents an incorrect connection. The correct pin header has one or more pins in the header removed or clipped to indicate a key for correct orientation, in absence of a pin 1 designation on the header, if a designation is missing from the header, the PCB may have a marking indicating orientation. For multi-row pin headers, the pin number is more complex, typically for headers attached to ribbon cables, the pins are numbered so they go linearly across the cable. Because of the way the connector attaches to the cable, this means in a header, pins in one row have odd numbers
7.
RS-232
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In telecommunications, RS-232 is a standard for serial communication transmission of data. It formally defines the signals connecting between a DTE such as a terminal, and a DCE, such as a modem. The RS-232 standard is used in computer serial ports. The standard defines the characteristics and timing of signals, the meaning of signals. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. An RS-232 serial port was once a feature of a personal computer, used for connections to modems, printers, mice, data storage, uninterruptible power supplies. However, RS-232 is hampered by low speed, large voltage swing. In modern personal computers, USB has displaced RS-232 from most of its peripheral interface roles, nevertheless, RS-232 devices are still used, especially in industrial machines, networking equipment, and scientific instruments. Interface mechanical characteristics, pluggable connectors and pin identification, functions of each circuit in the interface connector. Standard subsets of interface circuits for selected telecom applications, the standard does not define such elements as the character encoding, the framing of characters, transmission order of bits, or error detection protocols. The character format and transmission bit rate are set by the serial port hardware which may also contain circuits to convert the internal logic levels to RS-232 compatible signal levels. The standard does not define bit rates for transmission, except that it says it is intended for bit rates lower than 20,000 bits per second, RS-232 was first introduced in 1960 by the Electronic Industries Association as a Recommended Standard. The original DTEs were electromechanical teletypewriters, and the original DCEs were modems, when electronic terminals began to be used, they were often designed to be interchangeable with teletypewriters, and so supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of these devices, the resulting common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of breakout boxes, patch boxes, test equipment, books, a common deviation from the standard was to drive the signals at a reduced voltage. Some manufacturers therefore built transmitters that supplied +5 V and −5 V, later personal computers started to make use of the standard so that they could connect to existing equipment. For many years, an RS-232-compatible port was a feature for serial communications, such as modem connections. It remained in use into the late 1990s
8.
IBM PC compatible
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IBM PC compatible computers are those similar to the original IBM PC, XT, and AT, able to run the same software and support the same expansion cards as those. Such computers used to be referred to as PC clones, or IBM clones, Columbia Data Products built the first clone of the IBM personal computer by a clean room implementation of its BIOS. Early IBM PC compatibles used the computer bus as the original PC. The IBM AT compatible bus was named the Industry Standard Architecture bus by manufacturers of compatible computers. The term IBM PC compatible is now a historical description only, only the Apple Macintosh classic Mac OS and macOS kept significant market share without compatibility with the IBM personal computer, so consumers are typically identified as being a PC or Mac user. IBM decided in 1980 to market a low-cost single-user computer as quickly as possible in response to Apple Computers success in the microcomputer market. On 12 August 1981, the first IBM PC went on sale, there were three operating systems available for it. The least expensive and most popular was PC DOS made by Microsoft, in a crucial concession, IBMs agreement allowed Microsoft to sell its own version, MS-DOS, for non-IBM computers. The only component of the original PC architecture exclusive to IBM was the BIOS and this software would run on any machine using MS-DOS or PC-DOS. Software that directly addressed the hardware instead of making standard calls was faster, however, software addressing IBM PC hardware in this way would not run on MS-DOS machines with different hardware. The 808x computer marketplace rapidly excluded all machines which were not hardware-, the 640 KB barrier on conventional system memory available to MS-DOS is a legacy of that period, other non-clone machines, while subject to a limit, could exceed 640 kB. Rumors of lookalike, compatible computers, created without IBMs approval, by June 1983 PC Magazine defined PC clone as a computer accommodate the user who takes a disk home from an IBM PC, walks across the room, and plugs it into the foreign machine. Because of a shortage of IBM PCs that year, many customers purchased clones instead, Columbia Data Products produced the first computer more or less compatible to the IBM PC standard during June 1982, soon followed by Eagle Computer. Compaq announced its first IBM PC compatible in November 1982, the Compaq Portable, the Compaq was the first sewing machine-sized portable computer that was essentially 100% PC-compatible. The company could not copy the BIOS directly as a result of the decision in Apple v. Franklin. Each computer would have its own Original Equipment Manufacturer version of MS-DOS, any software written for MS-DOS would operate on any MS-DOS computer, despite variations in hardware design. This expectation seemed reasonable in the marketplace of the time. Until then Microsoft was based primarily on computer languages such as BASIC, the established small system operating software was CP/M from Digital Research which was in use both at the hobbyist level and by the more professional of those using microcomputers
9.
16550 UART
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The 16550 UART is an integrated circuit designed for implementing the interface for serial communications. The corrected -A version was released in 1987 by National Semiconductor and it was the first serial chip used in the IBM PS/2 line, which were introduced in 1987. The part was made by National Semiconductor. Similarly numbered devices, with varying levels of compatibility with the original National Semiconductor part, are made by other manufacturers, replacement of the factory-installed 8250 UART was a common upgrade for owners of IBM PC, XT, and compatible computers when high-speed modems became available. At speeds higher than 9600 baud, owners discovered that the ports of the computers were not able to handle a continuous flow of data without losing characters. Main features of the 16550 include, The ability to data from serial to parallel. An on-chip bit rate generator to control transmit and receive data rate, handshake lines for control of an external modem, controllable by software. An interrupt function to the host microprocessor, an on-chip FIFO buffer for both incoming and outgoing data, this gives the host system more time to respond to an interrupt generated by the UART, without loss of data. Both the computer hardware and software interface of the 16550 are backward compatible with the earlier 8250 UART and 16450 UART, the current version by Texas Instruments which bought National Semiconductor is called the 16550D. The 16550A and newer is pin compatible with the 16450, but the Microsoft diagnostics program supplied with MS-DOS6. x, Windows-9x, Windows-Me, and Windows-2000 often report the 16450 chip as a 8250 chip. One drawback of the earlier 8250 UARTs and 16450 UARTs was that interrupts were generated for each byte received and this generated high rates of interrupts as transfer speeds increased. More critically, with only a 1-byte buffer there is a risk that a received byte will be overwritten if interrupt service delays occur. To overcome these shortcomings, the 16550 series UARTs incorporated a 16-byte FIFO buffer with a programmable interrupt trigger of 1,4,8, the original 16550 had a bug that prevented this FIFO from being used. National Semiconductor later released the 16550A which corrected this issue, not all manufacturers adopted this nomenclature, however, continuing to refer to the fixed chip as a 16550. According to another source, the FIFO issue was corrected only in the 16550AF model, the 16550AFN model added DMA transfers. PC16550D UART, Texas Instruments / National Semiconductor Serial UART, an introduction Serial Programming/8250 UART Programming
10.
Integrated circuit
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An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material, normally silicon. The ICs mass production capability, reliability and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of using discrete transistors. ICs are now used in all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other home appliances are now inextricable parts of the structure of modern societies, made possible by the small size. These advances, roughly following Moores law, allow a computer chip of 2016 to have millions of times the capacity, ICs have two main advantages over discrete circuits, cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography rather than being constructed one transistor at a time, furthermore, packaged ICs use much less material than discrete circuits. Performance is high because the ICs components switch quickly and consume little power because of their small size, the main disadvantage of ICs is the high cost to design them and fabricate the required photomasks. This high initial cost means ICs are only practical when high production volumes are anticipated, Circuits meeting this definition can be constructed using many different technologies, including thin-film transistor, thick film technology, or hybrid integrated circuit. However, in general usage integrated circuit has come to refer to the single-piece circuit construction originally known as a integrated circuit. Jacobi disclosed small and cheap hearing aids as typical industrial applications of his patent, an immediate commercial use of his patent has not been reported. The idea of the circuit was conceived by Geoffrey Dummer. Dummer presented the idea to the public at the Symposium on Progress in Quality Electronic Components in Washington and he gave many symposia publicly to propagate his ideas, and unsuccessfully attempted to build such a circuit in 1956. A precursor idea to the IC was to create small ceramic squares, Components could then be integrated and wired into a bidimensional or tridimensional compact grid. This idea, which seemed very promising in 1957, was proposed to the US Army by Jack Kilby, however, as the project was gaining momentum, Kilby came up with a new, revolutionary design, the IC. In his patent application of 6 February 1959, Kilby described his new device as a body of semiconductor material … wherein all the components of the circuit are completely integrated. The first customer for the new invention was the US Air Force, Kilby won the 2000 Nobel Prize in Physics for his part in the invention of the integrated circuit. His work was named an IEEE Milestone in 2009, half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilbys had not. Noyces design was made of silicon, whereas Kilbys chip was made of germanium, Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation, a key concept behind the IC
11.
Device file
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In Unix-like operating systems, a device file or special file is an interface for a device driver that appears in a file system as if it were an ordinary file. There are also special files in MS-DOS, OS/2, and Microsoft Windows and they allow software to interact with a device driver using standard input/output system calls, which simplifies many tasks and unifies user-space I/O mechanisms. Device files often provide simple interfaces to peripheral devices such as printers and serial ports, finally, device files are useful for accessing system resources that have no connection with any actual device such as data sinks and random number generators. MS-DOS borrowed the concept of files from Unix but renamed them devices. Because early versions of MS-DOS did not support a directory hierarchy and this means that certain file names were reserved for devices, and should not be used to name new files or directories. The reserved names themselves were chosen to be compatible with special handling of PIP command in CP/M. There were two kinds of devices in MS-DOS, Block Devices and Character Devices, PIPE, MAILSLOT, and MUP are other standard Windows devices. There are two kinds of device files in Unix-like operating systems, known as character special files. The difference between them lies in how data written to them and read them is processed by the operating system. These together can be called device files in contrast to named pipes. Device nodes correspond to resources that an operating systems kernel has already allocated, Unix identifies those resources by a major number and a minor number, both stored as part of the structure of a node. The assignment of numbers occurs uniquely in different operating systems. Generally, the major number identifies the driver and the minor number identifies a particular device that the driver controls, in this case. However, in the presence of number allocation, this may not be the case. As with other file types, the computer system accesses device nodes using standard system calls. Character special files or character devices provide unbuffered, direct access to the hardware device and they do not necessarily allow programs to read or write single characters at a time, that is up to the device in question. The character device for a disk, for example, will normally require that all reads and writes are aligned to block boundaries. Block special files or block devices provide buffered access to hardware devices, unlike character devices, block devices will always allow the programmer to read or write a block of any size and any alignment
12.
Parallel port
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A parallel port is a type of interface found on computers for connecting peripherals. The name refers to the way the data is sent, parallel ports send multiple bits of data at once, in parallel communication, as opposed to serial interfaces that send bits one at a time. To do this, parallel ports require multiple data lines in their cables and port connectors, there are many types of parallel ports, but the term has become most closely associated with the printer port or Centronics port found on most personal computers from the 1970s through the 2000s. Today, the port interface is virtually non-existent because of the rise of Universal Serial Bus devices, along with network printing using Ethernet. The parallel port interface was originally known as the Parallel Printer Adapter on IBM PC-compatible computers and it was primarily designed to operate printers that used IBMs 8-bit extended ASCII character set to print text, but could also be used to adapt other peripherals. Graphical printers, along with a host of other devices, have designed to communicate with the system. An Wang, Robert Howard and Prentice Robinson began development of a low-cost printer at Centronics, the printer used the dot matrix printing principle, with a print head consisting of a vertical row of seven metal pins connected to solenoids. When power was applied to the solenoids, the pin was pulled forward to strike the paper and leave a dot. On their original design, a typical glyph was printed as a matrix seven high and five wide, while the A models used a print head with 9 pins and this left the problem of sending the ASCII data to the printer. While a serial port does so with the minimum of pins and wires, it requires the device to buffer up the data as it arrives bit by bit, a parallel port makes this simpler, the entire ASCII value is presented on the pins in complete form. In addition to the seven pins, the system also needed various control pins as well as electrical grounds. Wang happened to have a stock of 20,000 Amphenol 36-pin micro ribbon connectors that were originally used for one of their early calculators. The interface only required 21 of these pins, the rest were grounded or not connected, the connector has become so closely associated with Centronics that it is now popularly known as the Centronics connector. The Centronics Model 101 printer, featuring this connector, was released in 1970, the host sent ASCII characters to the printer using 7 of 8 data pins, pulling them high to +5V to represent a 1. When the data was ready, the host pulled the STROBE pin low, the printer responded by pulling the BUSY line high, printing the character, and then returning BUSY to low again. The host could send another character. Control characters in the data caused other actions, like the CR or EOF, the host could also have the printer automatically start a new line by pulling the AUTOFEED line high, and keeping it there. The host had to watch the BUSY line to ensure it did not feed data to the printer too rapidly, especially given variable-time operations like a paper feed
13.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
