computed axial tomography \t3-'mag-r3-fe\ (CAT) or com¬ puted tomography (CT) Diagnostic imaging method using a low-dose beam of X-rays that crosses the body in a single plane at many different angles. Conceived by William Oldendorf and developed independently by Godfrey Hounsfleld (b. 1919) and Allan M. Cormack (b. 1924), who shared a 1979 Nobel Prize for their inventions, this major advance in imaging technology became generally available in the early 1970s. Detec¬ tors record the strength of the exiting X-rays; this information is then pro¬ cessed by computer to produce a detailed two-dimensional cross-sectional image of the body. A series of such images in parallel planes or around an axis can show the location of abnormalities (especially tumours and other masses) more precisely than can conventional X-ray images.
computer Programmable machine that can store, retrieve, and process data. Today’s computers have at least one CPU that performs most cal¬ culations and includes a main memory, a control unit, and an arithmetic logic unit. Increasingly, personal computers contain specialized graphic processors, with dedicated memory, for handling the computations needed to display complex graphics, such as for three-dimensional simulations and games. Auxiliary data storage is usually provided by an internal hard disk and may be supplemented by other media such as floppy disks or CD-ROMs. Peripheral equipment includes input devices (e.g., keyboard, mouse) and output devices (e.g., monitor, printer), as well as the circuitry and cabling that connect all the components. Generations of computers are characterized by their technology. First-generation digital computers, developed mostly in the U.S. after World War II, used vacuum tubes and were enormous. The second generation, introduced c. 1960, used transis¬ tors and were the first successful commercial computers. Third-generation
computers (late 1960s and 1970s) were characterized by miniaturization of components and use of integrated circuits. The microprocessor chip, introduced in 1974, defines fourth-generation computers. See illustration on following page.
computer, analog See analog computer computer, digital See digital computer
computer-aided software engineering See CASE
computer animation also known as computer generated images (CGI) Form of animated graphics that has replaced “stop- motion” animation of scale-model puppets or drawings. Efforts to lessen the labour and costs of animation have led to simplification and comput¬ erization. Computers can be used in every step of sophisticated animation—for example, to automate the movement of the rostrum cam¬ era or to supply the in-between drawings for full animation. When a three-dimensional figure is translated into computer terms (digitized), the computer can generate and display a sequence of images that seem to move or rotate the object through space. Hence computer animation can simulate highly complex motion for medical and other scientific research¬ ers, as well as for feature films.
computer architecture Internal structure of a digital computer, encompassing the design and layout of its instruction set and storage reg¬ isters. The architecture of a computer is chosen with regard to the types of programs that will be run on it (business, scientific, general-purpose, etc.). Its principal components or subsystems, each of which could be said to have an architecture of its own, are input/output, storage, communica¬ tion, control, and processing.
computer art Manipulation of computer-generated images (pictures, designs, scenery, portraits, etc.) as part of a purposeful creative process. Specialized software is used together with interactive devices such as digital cameras, optical scanners, styli, and electronic tablets. Because graphic images require large programs, the computers used in such work are generally among the fastest and most powerful available. Computer art has wide applications in advertising, publishing, and film.
computer-assisted instruction Use of instructional material pre¬ sented by a computer. Since the advent of microcomputers in the 1970s, computer use in schools has become widespread, from primary schools through the university level and in some preschool programs. Instructional computers either present information or fill a tutorial role, testing the stu¬ dent for comprehension. By providing one-on-one interaction and pro¬ ducing immediate responses to input answers, computers allow students to demonstrate mastery and learn new material at their own pace. A dis¬ advantage is that computerized instruction cannot extend the lesson beyond the limits of the programming.
computer chip or chip Integrated circuit or small wafer of semicon¬ ductor material embedded with integrated circuitry. Chips comprise the processing and memory units of the modem digital computer (see micro¬ processor; RAM). Chip making is extremely precise and is usually done in a “clean room,” since even microscopic contamination could render the chip defective. As transistor components have shrunk, the number per chip has doubled about every 18 months (a phenomenon known as Moore’s law), from a few thousand in 1971 (Intel Corp.’s first chip) to millions by 1989. Nanotechnology is expected to make transistors even smaller and chips correspondingly more powerful in the 21st century.
computer circuitry Complete path or combination of interconnected paths for electron flow in a computer. Computer circuits are binary in concept, having only two possible states. They use on-off switches (tran¬ sistors) that are electrically opened and closed in nanoseconds and pico¬ seconds (billionths and trillionths of a second). A computer’s speed of operation depends on the design of its circuitry. Faster rates are achieved by shortening the time it takes to open and close the switches and by developing circuit paths that can handle the increased speeds.
computer graphics Use of computers to produce visual images, or the images so produced. Creating computer graphics requires a digital computer to store and manipulate images, a display screen, input/output devices, and specialized software that enables the computer to draw, colour, and manipulate images held in memory. Common computer graphic formats include GIF and JPEG, for single images, and MPEG and Quicktime, for multiframe images. The field has widespread use in business, scientific research, and entertainment. Monitors attached to CAD/CAM systems
© 2006 Encyclopaedia Britannica, Inc.
444 I computer-integrated manufacturing ► computer science
computer tower
monitor
power supply
cooling fan
external
speaker
CD/DVD- ROM drive
ribbon cable
battery
keyboard
scroll wheel
expansion slots ——
_micro¬ processor
cooling
blades
video card
mouse
mechanical mouse
(bottom view)
network card
right click switch scroll wheel —
USB
connector
motherboard
roller
internal speaker
cooling fan
encoder
left x
click
switch
ball
(rolls on surface)
read/write head
cable
hard drive
spindle.
PS/2
connector
circuit
board
saved file
optical mouse
(bottom view)
actuator
outer/
casing
camera
light beam (reflects from surface)
prism
circuit board
A typical personal computer system consists of the computer itself, a video monitor, a keyboard, a mouse, and speakers. Other peripheral devices may include a printer, scanner, camera, microphone, or external storage device. Chips and circuit boards ("cards") are plugged into the motherboard. Other components, such as disk drives, are housed in the computer case and controlled by a card called a controller. The microprocessor directs the computer's activity via the motherboard and processes data with its millions of transistors. Data and programs in use are stored in the RAM chips. The floppy and hard drives store data not in immediate use on magnetic disks. Opti¬ cal disks, such as CD-ROMs and DVDs, may store data as well. Some circuit boards are dedicated to specific functions; the sound card, for example, generates sounds and music. Additional boards, such as a modem, may be added by inserting them into an expansion slot, a row of electrical connectors into which the board is plugged. The mouse is an input device used to position a pointer on the computer's screen. On-screen selections are made by "clicking" one of the mouse's buttons, sending a signal to the computer.