Dictionary of Information Technology

In library science, a summary of a book, periodical feature, report or learned paper. AC See alternating current, accumulator. academy aperture In cinematography, the size of the frame mask in 35mm cameras and projectors as standardized by the Academy of Motion Picture Arts and Sciences. See mask. academy leader In filming, special motion picture leader with numbered frames spaced one second apart, for cueing film for projection and television broadcasting. See leader. academy standards In cinematography, standards established by the Academy of Motion Picture Arts and Sciences for film leaders, projectors and camera apertures. See film leader. accelerated motion In cinematography, pertaining to action photographed while the camera filming rate was progressively reduced. acceleration potential In electronics, the voltage between the cathode in a cathode ray tube, CRT, and the face of the tube which attracts the beam of focused electrons causing them to impinge on the phosphor dots. See CRT, phosphor dots. acceleration time In computing, that part of access time required to bring an auxiliary storage device, typically a tape drive, to the speed at which data can be read or written. See access time, tape drive. accent In typesetting, a mark used to indicate a specific sound value, stress or pitch, or to indicate that an ordinarily mute vowel should be pronounced. acceptance angle In photography, the angle in two dimensions covered by a lens or light meter. acceptance testing In computing, a series of tests designed to demonstrate the functional capabilities of a new computer system. It is usually conducted by the manufacturer to show the customer that the system is in working order. access (1) In computing, the manner in which files or data sets are referred to by the computer. (2) In communications, the public availability of cable broadcasting time in the US. See direct access, sequential access. access arm In computing, a mechanical device in a disk drive that positions the reading and writing mechanisms. See disk drive, head. access barred In data communications, a data facility which permits a terminal installation to make outgoing, or receive incoming, calls but not both. access charge In communications, a charge made by a common carrier for the use of its local exchange facilities. See common carrier, local exchange. access control In computer networks, the control of system usage, imposed by hardware, software and administrative controls. Such controls include system monitoring, user identification, ensuring data integrity, recording system access and changes and methods for granting user access. See hardware, software. accession number In library science, an arbitrary serial number given to each item as it enters a collection. See aspect card. access line In communications, a telecommunication line that continuously connects a remote station to a switching exchange. A telephone number is associated with such lines. access mechanism In computing, a mechanism for moving read and write heads to the requisite position on the storage device, or moving the storage medium to the heads, so that data may be accessed. access time (1) In computing, the time interval from the instant that data is requested from a storage device to the instant it is delivered to the CPU, and vice versa. (2) In recording, the time interval between the moment that information is requested in playback to the moment that it is delivered. See CPU. accordion fold In computing, a method of folding paper in which each fold is in the opposite direction to the previous one. A printer or paper tape reader can be fed with accordion folded paper without continuous operator intervention. Synonymous with concertina fold, fanfold. accumulator In computing, a device that functions as a holding register for arithmetic, logical and input output acknowledgement 3 operations. Normally data words fetched from memory are loaded into the accumulator and words to be stored into memory are first loaded into this register. See input output, register. accuracy The degree of exactness of an approximation or measurement. It denotes the absolute quality of the result with respect to its true value, as compared with precision which is concerned with the amount of detail used in specifying a result. Thus a two digit result may be ntore accurate than an incorrect three digit result, but it will be less precise. See precision. acldc ringing In telephony, a method of telephone ringing that uses alternating current to operate a ringer and direct current to activate a relay that stops the ringing when the called party answers. See relay. ACE Association of Cinema Editors. acetate base In cinematography, the modern, slow burning base material used for motion picture films, and, in sheet form, for eels in animation work. See eel. acetone In cinematography, an organic liquid chemical used in the manufacture of some types of film cement and used to clean film splicing equipment. achromatic In optics, pertaining to an optical device, e.g. a lens, which has been corrected in manufacture for chromatic aberration. See chromatic aberration. ACK See acknowledge character. acknowledge character In data communications, a transmission character transmitted by a station as an affirmative response to the station with which the connection has been set up. Compare negative acknowledgement. See acknowledgement, station. acknowledgement In data communications, the transmission by a receiver of acknowledge characters as a response to a sender. See affirmative acknowledgement, negative acknowledgement.