Printer

Printer, a computerperipheral that puts text or a computer-generated image on paper or on another medium, such as a transparency. Printers can be categorized in any of several ways. The most common distinction is impact vs. nonimpact. Impact printers physically strike the paper and are exemplified by pin dot-matrix printers and daisy-wheel printers; nonimpact printers include every other type of print mechanism, including laser, ink-jet, and thermal printers. Other possible methods of categorizing printers include (but are not limited to) the following: Print technology: Chief among these, with microcomputers, are pin dot-matrix, ink-jet, laser, thermal, and (although somewhat outdated) daisy-wheel or thimble printers. Pin dot-matrix printers can be further classified by the number of pins in the print head: 9, 18, 24, and so on. Character formation: Fully formed characters made of continuous lines (for example, those produced by a daisy-wheel printer) vs. dot-matrix characters composed of patterns of dots (such as those produced by standard dot-matrix, ink-jet, and thermal printers). Laser printers, while technically dot-matrix, are generally considered to produce fully formed characters because their output is very clear and the dots are extremely small and closely spaced. Method of transmission: parallel (byte-by-byte transmission) vs. serial (bit-by-bit transmission). These categories refer to the means by which output is sent to the printer rather than to any mechanical distinctions. Many printers are available in either serial or parallel versions, and still other printers offer both choices, yielding greater flexibility in installation options. Method of printing: Character by character, line by line, or page by page. Character printers include standard dot-matrix, ink-jet, thermal, and daisy-wheel printers. Line printers include the band, chain, and drum printers that are commonly associated with large computer installations or networks. Page printers include the electrophotographic printers, such as laser printers. Print capability: Text-only vs. text-and-graphics. Text-only printers, including most daisy-wheel and thimble printers and some dot-matrix and laser printers, can reproduce only characters for which they have matching patterns, such as embossed type, or internal character maps. Text-andgraphics printers—dot-matrix, ink-jet, laser, and others—can reproduce all manner of images by “drawing” each as a pattern of dots. Dot-Matrix Printer, in computer science, any printer that produces characters made up of dots using a wire-pin print head. The quality of output from a dot-matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot-matrix printers are often categorized by the number of pins in the print head—typically 9, 18, or 24. Laser Printer, an electrophotographic printer that is based on the technology used by photocopiers. A focused laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrical charge is removed from the drum and the excess toner is collected. By omitting this final step and repeating only the toner-application and paper-handling steps, the printer can make multiple copies.

The only serious drawback of a laser printer is that it offers less paper-handling flexibility than do dot-matrix printers. Both multipart forms and wide-carriage printing, for example, are better handled by dot-matrix or daisy-wheel printers. Printer Driver, in computer science, a computer software program designed to enable other programs to work with a particular printer without concerning themselves with the specifics of the printer's hardware and internal “language.” Different printers require different codes and commands to operate properly and to provide access to their special features and abilities. Application programs can communicate properly with a variety of printers by using printer drivers, which handle all of the subtleties of each printer so that the application program doesn't have to. Today, graphical user interfaces offer their own printer drivers, eliminating the need for an application that runs under the interface to have its own printer driver. Interface, the point at which a connection is made between two elements so that they can work with one another. In computing, different types of interfacing occur on different levels, ranging from highly visible user interfaces that enable people to communicate with programs to often invisible, yet necessary, hardware interfaces that connect devices and components inside the computer. At less visible software levels within the computer are other types of interfaces, such as those that enable an application to work with the operating system and those that enable an operating system to work with the computer's hardware. In hardware, interfaces are cards, plugs, and other devices that connect pieces of hardware with the computer so that information can be moved from place to place. There are, for example, standardized data-transfer interfaces, such as RS-232-C and SCSI, that enable connections between computers and printers, hard disks, and other devices. On the conceptual level, networking and communications standards such as the ISO Open Systems Interconnection (OSI) model combine hardware and software guidelines to enable entire systems and their associated devices to connect with one another. Although the ISO/OSI model and other guidelines are not literal, physical interfaces, they define ways for different systems to connect and communicate. Peripheral, in computer science, a term used for devices, such as disk drives, printers, modems, and joysticks, that are connected to a computer and are controlled by its microprocessor. Although peripheral often implies “additional but not essential,” many peripheral devices are critical elements of a fully functioning and useful computer system. Few people, for example, would argue that disk drives are nonessential, although computers can function without them. Keyboards, monitors, and mice are also strictly considered peripheral devices, but because they represent primary sources of input and output in most computer systems, they can be considered more as extensions of the system unit than as peripherals. Disk Drive, in computer science, a device that reads or writes data, or both, on a disk medium. The disk medium may be either magnetic, as with floppy disks or hard disks; optical, as with CDROM (compact disc-read only memory) disks; or a combination of the two, as with magneto-

optical disks. Nearly all computers come equipped with drives for these types of disks, and the drives are usually inside the computer, but may also be connected as external, or peripheral, devices. The main components of a disk drive are the motor, which rotates the disk; the read-write mechanism; and the logic board, which receives commands from the operating system to place or retrieve information on the disk. To read or write information to a disk, drives use various methods. Floppy and hard drives use a small magnetic head to magnetize portions of the disk surface, CD-ROM and WORM (Write-Once-Read-Many) drives use lasers to read information, and magneto-optical drives use a combination of magnetic and optical techniques to store and retrieve information. Floppy and hard disk drives store information on magnetic disks. The disk itself is a thin, flexible piece of plastic with tiny magnetic particles imbedded in its surface. To write data to the disk, the read-write head creates a small magnetic field that aligns the magnetic poles of the particles on the surface of the disk directly beneath the head. Particles aligned in one direction represent a 0 while particles aligned in the opposite direction represent a 1. To read data from a disk, the drive head scans the surface of the disk. The magnetic fields of the particles in the disk induce an alternating electric current in the read-write head, which is then translated into the series of 1s and 0s that the computer understands. Unlike hard or floppy disks, most CD-ROM drives are unable to write data to the CD. Data is initially written to CD-ROM discs by burning microscopic pits into the disc's reflective surface with a laser. To read the information contained on the disc, the drive shines a low-power laser beam onto the surface. When the laser light hits flat spots on the reflective surface of the CD, it bounces back to a photo detector, which records the impulse as a 0. When the laser light hits pits in the surface, it does not reflect light back to the photo detector, and this absence of light corresponds to a 1. Most CD-ROM drives are only capable of reading data and cannot write data to the CD. WORM drives, however, are able to both etch blank CDs and to read data from them. Magneto-optical (MO) drives combine optical and magnetic technology to read from and write to disks that have the appearance of CD-ROMs in plastic, floppy-disk cases. MO drives can rewrite the MO disks without limitation just as magnetic drives rewrite magnetic media. Although more expensive than standard magnetic or optical drives, MO drives combine speed, large capacity, and high durability of data Input/Output Device, in computer science, a piece of hardware that is used for both providing information to the computer and receiving information from it. An input/output device thus transfers information in one of two directions depending on the current situation. A disk drive is an example of an input/output device. Some devices, called input devices, can be used only for input —for example, a keyboard, a mouse, a light pen, and a joystick. Other devices, called output devices, can be used only for output—for example, a printer and a monitor. Most devices require the installation of software routines called device drivers, which allow the computer to transmit and receive information to and from the device. Mouse (computer), a common pointing device, popularized by its inclusion as standard equipment with the Apple Macintosh. With the rise in popularity of graphical user interfaces (Graphical User Interface) in MS-DOS; UNIX, and OS/2, use of mice is growing throughout the

personal computer and workstation worlds. The basic features of a mouse are a casing with a flat bottom, designed to be gripped by one hand; one or more buttons on the top; a multidirectional detection device (usually a ball) on the bottom; and a cable connecting the mouse to the computer. See the illustration. By moving the mouse on a surface (such as a desk), the user typically controls an on-screen cursor. A mouse is a relative pointing device because there are no defined limits to the mouse's movement and because its placement on a surface does not map directly to a specific screen location. To select items or choose commands on the screen, the user presses one of the mouse's buttons, producing a “mouse click Keyboard, in computer science, a keypad device with buttons or keys that a user presses to enter data characters and commands into a computer. Keyboards emerged from the combination of typewriter and computer-terminal technology. They are one of the fundamental pieces of personal computer (PC) hardware, along with the central processing unit (CPU), the monitor or screen, and the mouse or other cursor device. Floppy Disk, in computer science, a round, flat piece of Mylar coated with ferric oxide, a rustlike substance containing tiny particles capable of holding a magnetic field, and encased in a protective plastic cover, the disk jacket. Data is stored on a floppy disk by the disk drive's read/write head, which alters the magnetic orientation of the particles. Orientation in one direction represents binary 1; orientation in the other, binary 0. Typically, a floppy disk is 5.25 inches in diameter, with a large hole in the center that fits around the spindle in the disk drive. Depending on its capacity, such a disk can hold from a few hundred thousand to over one million bytes of data. A 3.5-inch disk encased in rigid plastic is usually called a microfloppy disk but can also be called a floppy disk Hard Disk Hard disks are used to record computer data magnetically. A hard disk drive consists of a stack of inflexible magnetic disks mounted on a motor. As the disks spin at high speeds, read/write heads at the end of a metal fork swing in and out to access sectors of the disks.

Hard Disk, in computer science, one or more inflexible platters coated with material that allows the magnetic recording of computer data. Hard disks provide faster access to data than floppy disks and are capable of storing much more information. Because platters are rigid, they can be stacked so that one hard-disk drive can access more than one platter. Most hard disks have from two to eight platters. .