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 personal computers, data was transferred through serial ports to devices such as modems and various peripherals. While such interfaces as Ethernet, FireWire, USB all send data as a serial stream, the term "serial port" identifies hardware more or less compliant to the RS-232 standard, intended to interface with a modem or with a similar communication device. Modern computers without serial ports may require USB-to-serial 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 serial port as a control console for diagnostics. Network equipment use serial console for configuration. Serial ports are still used in these areas as they are simple and their console functions are standardized and widespread.
A serial port requires 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. 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. Before large-scale integration UART integrated circuits were common, a minicomputer would have a serial port made of multiple small-scale integrated circuits to implement shift registers, logic gates and all the other logic for a serial port. Early home computers had proprietary serial ports with pinouts and voltage levels incompatible with RS-232. Inter-operation with RS-232 devices may be impossible as the serial port cannot withstand the voltage levels produced and may have other differences that "lock in" the user to products of a particular manufacturer. 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 mass storage and video devices. Many personal computer motherboards still have at least one serial port if accessible only through a pin header. 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 cheap and exist on a single chip, sometimes 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, 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 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, must be used. 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, female connectors have corresponding round sockets. Either type of connector can be mounted on a panel. Connectors mounted on DTE are to be male, those mounted on DCE are to be female. However, this is far from universal. While the RS-232 standard specified a 25-pin D-type connector, many designers of personal computers chose to implement only a subset of the full standard: they traded off compatibility with the standard against the use of less costly and more compact connectors; 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 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 and space. However, presence of a 9-pin D-subminiature connector is not sufficient to indicate the connection is in fact a serial port, since this connector is used for video and other purposes; some miniaturized electronics graphing calculators and hand-held amateur and two-way radio equipment, have serial ports using a phone connector the smaller 2.5 or 3.5 mm connectors and use the most basic 3-wire interface. Many models of Macintosh favor the related RS-422 standard using German mini-DIN connectors, except in the earliest models; the Macintosh included a standard set of two ports for connection to a printer and a modem, but some PowerBook laptops had only one combined port to save space. Since most devices do not use all of the 20 signals that are defined by the standard, smaller connectors are used. For example, the 9-pin DE-9 connector is used by most IBM-compatible PCs since the IBM PC AT, has been standardized as TIA-574.
More modular connectors have been used. Most comm
The Pilot 1000 and Pilot 5000 were the first generations of PDAs produced by Palm Computing. It was introduced in March 1996; the Pilot uses a Motorola 68328 processor at 16 MHz, had 128 kB or 512 kB built in Random-access memory. The PDA has a plastic case, its dimensions are 120x80x18 weight is 160 grams. The Pilot has a 160x160 pixel monochrome LCD tactile panel, with a "Graffiti input zone" presented in the bottom third of the screen. Underneath the screen sits four applications buttons and two scroll buttons. At left, contrast control. At right top, stylus slot. On the back of the device there is a Memory Slot door, Reset button, battery compartment and Serial Port. Memory is kept in a "memory slot" under a plastic cover at the back top of the PDA. A 512 kB ROM chip stores resident applications. RAM is available in 128 kB, 512 kB or 1 MB. Hardware limit is 12 MB of RAM and 4 MB of ROM. After a calibration test presented during the initial power up, the Pilot would boot and be ready for use and synchronization.
Connecting and synchronizing the PDA was done through a utility called Pilot Desktop. For the PC, Pilot Desktop was distributed either on 3½ inch disk or on CD-ROM. A version of Pilot Desktop now exists for use with the Mac platform and open source support exists for use on Linux distributions, as well. Palm, Inc. was sued by the Pilot pen company for using the name "Pilot". Palm was involved in a legal battle where Xerox filed suit for David Goldberg's "Unistroke" patent. Palm 3Com Palm Pilot Hardware Book 3Com Mac Desktop Handbook Palm Pilot 1000 Retrospective Memory Modules Pilot Desktop 1.0
The Hewlett-Packard Company or Hewlett-Packard was an American multinational information technology company headquartered in Palo Alto, California. It developed and provided a wide variety of hardware components as well as software and related services to consumers, small- and medium-sized businesses and large enterprises, including customers in the government and education sectors; the company was founded in a one-car garage in Palo Alto by Bill Hewlett and David Packard, produced a line of electronic test equipment. HP was the world's leading PC manufacturer from 2007 to Q2 2013, at which time Lenovo ranked ahead of HP. HP specialized in developing and manufacturing computing, data storage, networking hardware, designing software and delivering services. Major product lines included personal computing devices and industry standard servers, related storage devices, networking products, software and a diverse range of printers and other imaging products. HP directly marketed its products to households, small- to medium-sized businesses and enterprises as well as via online distribution, consumer-electronics and office-supply retailers, software partners and major technology vendors.
HP had services and consulting business around its products and partner products. Hewlett-Packard company events included the spin-off of its electronic and bio-analytical measurement instruments part of its business as Agilent Technologies in 1999, its merger with Compaq in 2002, the acquisition of EDS in 2008, which led to combined revenues of $118.4 billion in 2008 and a Fortune 500 ranking of 9 in 2009. In November 2009, HP announced the acquisition of 3Com, with the deal closing on April 12, 2010. On April 28, 2010, HP announced the buyout of Inc. for $1.2 billion. On September 2, 2010, HP won its bidding war for 3PAR with a $33 a share offer, which Dell declined to match. Hewlett-Packard spun off its enterprise products and services business as Hewlett Packard Enterprise on November 1, 2015. Hewlett-Packard held onto the PC and printer businesses, was renamed to HP Inc. Bill Hewlett and David Packard graduated with degrees in electrical engineering from Stanford University in 1935; the company originated in a garage in nearby Palo Alto during a fellowship they had with a past professor, Frederick Terman at Stanford during the Great Depression.
They considered Terman a mentor in forming Hewlett-Packard. In 1938, Packard and Hewlett begin part-time work in a rented garage with an initial capital investment of US$538. In 1939 Hewlett and Packard decided to formalize their partnership, they tossed a coin to decide whether the company they founded would be called Hewlett-Packard or Packard-Hewlett. HP incorporated on August 18, 1947, went public on November 6, 1957. Of the many projects they worked on, their first financially successful product, was a precision audio oscillator, the Model HP200A, their innovation was the use of a small incandescent light bulb as a temperature dependent resistor in a critical portion of the circuit, the negative feedback loop which stabilized the amplitude of the output sinusoidal waveform. This allowed them to sell the Model 200A for $89.40 when competitors were selling less stable oscillators for over $200. The Model 200 series of generators continued production until at least 1972 as the 200AB, still tube-based but improved in design through the years.
One of the company's earliest customers was Walt Disney Productions, which bought eight Model 200B oscillators for use in certifying the Fantasound surround sound systems installed in theaters for the movie Fantasia. They worked on counter-radar technology and artillery shell fuses during World War II, which allowed Packard to be exempt from the draft. HP is recognized as the symbolic founder of Silicon Valley, although it did not investigate semiconductor devices until a few years after the "traitorous eight" had abandoned William Shockley to create Fairchild Semiconductor in 1957. Hewlett-Packard's HP Associates division, established around 1960, developed semiconductor devices for internal use. Instruments and calculators were some of the products using these devices. During the 1960s, HP partnered with Sony and the Yokogawa Electric companies in Japan to develop several high-quality products; the products were not a huge success, as there were high costs in building HP-looking products in Japan.
HP and Yokogawa formed a joint venture in 1963 to market HP products in Japan. HP bought Yokogawa Electric's share of Hewlett-Packard Japan in 1999. HP spun off Dynac, to specialize in digital equipment; the name was picked so that the HP logo "hp" could be turned upside down to be a reverse reflect image of the logo "dy" of the new company. Dynac changed to Dymec, was folded back into HP in 1959. HP experimented with using Digital Equipment Corporation minicomputers with its instruments, but after deciding that it would be easier to build another small design team than deal with DEC, HP entered the computer market in 1966 with the HP 2100 / HP 1000 series of minicomputers; these had a simple accumulator-based design, with two accumulator registers and, in the HP 1000 models, two index registers. The series was produced for 20 years, in spite of several attempts to replace it, was a forerunner of the HP 9800 and HP 250 series of desktop and business computers; the HP 3000 was an advanced stack-based design for a business computing server redesigned with RISC technology.
The HP 2640 series of smart and intelligent terminals introduced forms-based interfaces to ASCII terminals, introduced screen labeled functio
Infrared Data Association
The Infrared Data Association is an industry-driven interest group, founded in 1993 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, the name "IrDA" refers to that set of protocols; the main reason for using IrDA had been wireless data transfer over the "last one meter" using point-and-shoot principles. Thus, it has been implemented in portable devices such as mobile telephones, cameras and medical devices. Main characteristics of this kind of wireless optical communication is physically secure data transfer, line-of-sight and low bit error rate that makes it efficient; the mandatory IrPHY is the physical layer of the IrDA specifications. It comprises optical link definitions, coding, cyclic redundancy check and the framer. Different data rates use different modulation/coding schemes: SIR: 9.6–115.2 kbit/s, asynchronous, RZI, UART-like, 3/16 pulse MIR: 0.576–1.152 Mbit/s, RZI, 1/4 pulse, HDLC bit stuffing FIR: 4 Mbit/s, 4PPM VFIR: 16 Mbit/s, NRZ, HHH UFIR: 96 Mbit/s, NRZI, 8b/10b GigaIR: 512 Mbit/s – 1 Gbit/s, NRZI, 2-ASK, 4-ASK, 8b/10bFurther characteristics are: Range: standard: 1 m.
The 10 GigaIR define new usage models that supports higher link distances up to several meters. Angle: minimum cone ±15° Speed: 2.4 kbit/s to 1 Gbit/s Modulation: baseband, no carrier Infrared window Wavelength: 850–900 nmThe frame size depends on the data rate and varies between 64 B and 64 kB. Additionally, bigger blocks of data can be transferred by sending multiple frames consecutively; this can be adjusted with a parameter called "window size". Data blocks up to 8 MB can be sent at once. Combined with a low bit error rate of <10−9, that communication could be efficient compared to other wireless solutions. IrDA transceivers communicate with infrared pulses in a cone that extends at least 15 degrees half angle off center; the IrDA physical specifications require the lower and upper limits of irradiance such that a signal is visible up to one meter away, but a receiver is not overwhelmed with brightness when a device comes close. In practice, there are some devices on the market that do not reach one meter, while other devices may reach up to several meters.
There are devices that do not tolerate extreme closeness. The typical sweet spot for IrDA communications is from 5 to 60 cm away from a transceiver, in the center of the cone. IrDA data communications operate in half-duplex mode because while transmitting, a device’s receiver is blinded by the light of its own transmitter, thus full-duplex communication is not feasible; the two devices that communicate simulate full-duplex communication by turning the link around. The primary device controls the timing of the link, but both sides are bound to certain hard constraints and are encouraged to turn the link around as fast as possible; the mandatory IrLAP is the second layer of the IrDA specifications. It lies below the IrLMP layer, it represents the data link layer of the OSI model. The most important specifications are: Access control Discovery of potential communication partners Establishing of a reliable bidirectional connection Distribution of the primary/secondary device roles Negotiation of QoS parametersOn the IrLAP layer the communicating devices are divided into a "primary device" and one or more "secondary devices".
The primary device controls the secondary devices. Only if the primary device requests a secondary device to send, is it allowed to do so; the mandatory IrLMP is the third layer of the IrDA specifications. It can be broken down into two parts. First, the LM-MUX, which lies on top of the IrLAP layer, its most important achievements are: Provides multiple logical channels Allows change of primary/secondary devicesSecond, the LM-IAS, which provides a list, where service providers can register their services so other devices can access these services by querying the LM-IAS. The optional Tiny TP lies on top of the IrLMP layer, it provides: Transportation of large messages by SAR Flow control by giving credits to every logical channel The optional IrCOMM lets the infrared device act like either a serial or parallel port. It lies on top of the IrLMP layer; the optional OBEX provides the exchange of arbitrary data objects between infrared devices. It lies on top of the Tiny TP protocol, so Tiny TP is mandatory for OBEX to work.
The optional IrLAN provides the possibility to connect an infrared device to a local area network. There are three possible methods: Access point Peer-to-peer HostedAs IrLAN lies on top of the Tiny TP protocol, the Tiny TP protocol must be implemented for IrLAN to work. IrSimple achieves at least 4 to 10 times faster data transmission speeds by improving the efficiency of the infrared IrDA protocol. A 500 KB normal picture from a cell phone can be transferred within 1 second. One of the primary targets of IrSimpleShot is to allow the millions of IrDA-enabled camera phones to wirelessly transfer pictures to printers, printer kiosks and flat-panel TVs. Infrared Financial Messaging is a wireless payment standard developed by the Infrared Data Association. IrDA was popular on PDAs, laptops and some desktops from the late 1990s through the earl
Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Toshiba developed flash memory from EEPROM in the early 1980s and introduced it to the market in 1984; the two main types of flash memory are named after the NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates. While EPROMs had to be erased before being rewritten, NAND-type flash memory may be written and read in blocks which are much smaller than the entire device. NOR-type flash allows a single machine word to be written – to an erased location – or read independently; the NAND type is found in memory cards, USB flash drives, solid-state drives, similar products, for general storage and transfer of data. NAND or NOR flash memory is often used to store configuration data in numerous digital products, a task made possible by EEPROM or battery-powered static RAM. One key disadvantage of flash memory is that it can only endure a small number of write cycles in a specific block.
Example applications of both types of flash memory include personal computers, PDAs, digital audio players, digital cameras, mobile phones, video games, scientific instrumentation, industrial robotics, medical electronics. In addition to being non-volatile, flash memory offers fast read access times, although not as fast as static RAM or ROM, its mechanical shock resistance helps explain its popularity over hard disks in portable devices, as does its high durability, ability to withstand high pressure and immersion in water, etc. Although flash memory is technically a type of EEPROM, the term "EEPROM" is used to refer to non-flash EEPROM, erasable in small blocks bytes; because erase cycles are slow, the large block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2013, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage.
Flash memory was invented by Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the name "flash" was suggested by Masuoka's colleague, Shōji Ariizumi, because the erasure process of the memory contents reminded him of the flash of a camera. Masuoka and colleagues presented the invention at the IEEE 1987 International Electron Devices Meeting held in San Francisco. Intel Corporation introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location; this makes it a suitable replacement for older read-only memory chips, which are used to store program code that needs to be updated, such as a computer's BIOS or the firmware of set-top boxes. Its endurance may be from as little as 100 erase cycles for an on-chip flash memory, to a more typical 10,000 or 100,000 erase cycles, up to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media.
NAND flash has reduced erase and write times, requires less chip area per cell, thus allowing greater storage density and lower cost per bit than NOR flash. However, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits; this makes NAND flash unsuitable as a drop-in replacement for program ROM, since most microprocessors and microcontrollers require byte-level random access. In this regard, NAND flash is similar to other secondary data storage devices, such as hard disks and optical media, is thus suitable for use in mass-storage devices, such as memory cards; the first NAND-based removable media format was SmartMedia in 1995, many others have followed, including: MultiMediaCard Secure Digital Memory Stick, xD-Picture Card. A new generation of memory card formats, including RS-MMC, miniSD and microSD, feature small form factors. For example, the microSD card has an area of just over 1.5 cm2, with a thickness of less than 1 mm.
As of August 2017 microSD cards with capacity up to 400 GB are available. Flash memory stores information in an array of memory cells made from floating-gate transistors. In single-level cell devices, each cell stores only one bit of information. Multi-level cell devices, including triple-level cell devices, can store more than one bit per cell; the floating gate may be non-conductive. In flash memory, each memory cell resembles a standard metal-oxide-semiconductor field-effect transistor except that the transistor has two gates instead of one; the cells can be seen as an electrical switch in which current flows between two terminals and is controlled by a floating gate and a control gate. The CG is similar to the gate in other MOS transistors, but below this, there is the FG insulated all around by an oxide layer; the FG is interposed between the MOSFET channel. Because the FG is electrically isolated by its insulating layer, electrons placed on it are trapped; when the FG is charged with electrons, this charge screens the electric field from the CG, inc
Personal digital assistant
A personal digital assistant known as a handheld PC, is a variety mobile device which functions as a personal information manager. PDAs were discontinued in the early 2010s after the widespread adoption of capable smartphones, in particular those based on iOS and Android. Nearly all PDAs have the ability to connect to the Internet. A PDA has an electronic visual display. Most models have audio capabilities, allowing usage as a portable media player, enabling most of them to be used as telephones. Most PDAs can access intranets or extranets via Wi-Fi or Wireless Wide Area Networks. Sometimes, instead of buttons, PDAs employ touchscreen technology; the technology industry has recycled the term personal digital assistance. The term is more used for software that identifies a user's voice to reply to the queries; the first PDA, the Organizer, was released in 1984 by Psion, followed by Psion's Series 3, in 1991. The latter began to resemble the more familiar PDA style, including a full keyboard; the term PDA was first used on January 7, 1992 by Apple Computer CEO John Sculley at the Consumer Electronics Show in Las Vegas, referring to the Apple Newton.
In 1994, IBM introduced the first PDA with full telephone functionality, the IBM Simon, which can be considered the first smartphone. In 1996, Nokia introduced a PDA with telephone functionality, the 9000 Communicator, which became the world's best-selling PDA. Another early entrant in this market was Palm, with a line of PDA products which began in March 1996. A typical PDA has a touchscreen for navigation, a memory card slot for data storage, IrDA, Bluetooth and/or Wi-Fi. However, some PDAs may not have a touchscreen, using softkeys, a directional pad, a numeric keypad or a thumb keyboard for input. To have the functions expected of a PDA, a device's software includes an appointment calendar, a to-do list, an address book for contacts, a calculator, some sort of memo program. PDAs with wireless data connections typically include an email client and a Web browser, may or may not include telephony functionality. Many of the original PDAs, such as the Apple Newton and Palm Pilot, featured a touchscreen for user interaction, having only a few buttons—usually reserved for shortcuts to often-used programs.
Some touchscreen PDAs, including Windows Mobile devices, had a detachable stylus to facilitate making selections. The user interacts with the device by tapping the screen to select buttons or issue commands, or by dragging a finger on the screen to make selections or scroll. Typical methods of entering text on touchscreen PDAs include: A virtual keyboard, where a keyboard is shown on the touchscreen. Text is entered by tapping the on-screen keyboard with stylus. An external keyboard connected via Infrared port, or Bluetooth; some users may choose a chorded keyboard for one-handed use. Handwriting recognition, where letters or words are written on the touchscreen with a stylus, the PDA converts the input to text. Recognition and computation of handwritten horizontal and vertical formulas, such as "1 + 2 =", may be a feature. Stroke recognition allows the user to make a predefined set of strokes on the touchscreen, sometimes in a special input area, representing the various characters to be input.
The strokes are simplified character shapes, making them easier for the device to recognize. One known stroke recognition system is Palm's Graffiti. Despite research and development projects, end-users experience mixed results with handwriting recognition systems; some find it frustrating and inaccurate, while others are satisfied with the quality of the recognition. Touchscreen PDAs intended for business use, such as the BlackBerry and Palm Treo also offer full keyboards and scroll wheels or thumbwheels to facilitate data entry and navigation. Many touchscreen PDAs support some form of external keyboard as well. Specialized folding keyboards, which offer a full-sized keyboard but collapse into a compact size for transport, are available for many models. External keyboards may attach to the PDA directly, using a cable, or may use wireless technology such as infrared or Bluetooth to connect to the PDA. Newer PDAs, such as the HTC HD2, Apple iPhone, Apple iPod Touch, Palm Pre, Palm Pre Plus, Palm Pixi, Palm Pixi Plus, Google Android include more advanced forms of touchscreen that can register multiple touches simultaneously.
These "multi-touch" displays allow for more sophisticated interfaces using various gestures entered with one or more fingers. Although many early PDAs did not have memory card slots, now most have either some form of Secure Digital slot, a CompactFlash slot or a combination of the two. Although designed for memory, Secure Digital Input/Output and CompactFlash cards are available that provide accessories like Wi-Fi or digital cameras, if the device can support them; some PDAs have a USB port for USB flash drives. Some PDAs use microSD cards, which are electronically compatible with SD cards, but have a much smaller physical size. While early PDAs connected to a user's personal computer via serial ports or another proprietary connection, many today connect via a USB cable. Older PDAs were unable to connect to each other via USB, as their implementations of USB didn't support acting as the "host"; some early PDAs were able to connect to the Internet indirectly by means of an external modem connected via the PDA's serial port or "sync" connector, or directly by using an expansion card that provided an Ethernet port.
Most modern PDAs have a popular wireless protocol for mobile devices. Bluetooth can be used to connect keyboards, headsets, GPS receiver