Recording and Reproduction of Information
Recording and Reproduction of Information
(also information recording and retrieval), processes by means of which information is entered and stored in a physical object for subsequent reproduction. As human society develops, increasingly wide use is being made of various forms of recording and reproduction of information. Before the 19th century, information was recorded only through graphics, that is, the transformation of information into a system of visually perceived symbols (drawings, hieroglyphs, signs, letters, digits, and so on). All of these forms are still being used extensively today. Printing subsequently developed from such forms. Books, magazines, and newspapers published in millions of copies have become a powerful medium of instruction and mass information.
The invention of photography (the French inventor L. Daguerre, 1839) and the first sound-recording device, the phonograph (the American inventor T. A. Edison, 1877), produced a fundamental revolution in the principles of recording and reproduction of information. The automation of the very processes of recording and reproduction of information became possible; the operator’s role was reduced to the performance of preparatory and subsidiary operations.
The process of recording information is based on the fact that signals representing information are stored in the form of corresponding stable changes in the state or form of a particular body (the data carrier), and the stored information is reproduced by the production of new signals corresponding to the changes. Such changes may be produced simultaneously throughout the entire carrier or successively in its individual parts. Devices of the first type include equipment for photography and filming, which store images “as a whole,” as well as devices based on the principle of holography. Devices of the second type are called data recording and reproduction apparatus. The carrier in such devices may be either fixed or movable relative to the recording and pickup components, by means of which signals act on the carrier (in recording) or are “read” from the carrier (in reproduction).
A fixed carrier has a discrete structure. It consists of components with two or more stable states (relays, ferrite cores, flip-flops, and so on) and is used principally in the memories of electronic computers. A movable carrier is macroscopically continuous. It may be a magnetic tape, motion-picture film, or a flexible disk. Despite differences in equipment, units for recording and reproduction of data with movable carriers have identical block diagrams (see Figure 1). The source (1) of the information being recorded usually creates signals of various physical natures. Electrical signals are most suitable for transmission and transformation. Therefore, in unit (2) the information being recorded is transformed into electrical signals; in unit (3) the signals are amplified and, through a recording component (4) such as a stylus or magnetic head, act on the movable carrier (5), leaving a trace on it, which is called the recording track. The carrier, together with the recording track that has been produced, is called a signal track, in particular cases, a sound track (in sound recording) or video track (in recording image signals). During reproduction the signal track (5), moving with the same speed as during recording and acting directly on the reproducing component (6)—the sound pick-up or magnetic head—produces signals in it that contain the recorded information. The received signals are transformed into electrical signals in unit (7); component (6) and unit (7) are frequently structurally combined. After amplification and further transformation in unit (8), signals arrive at either a device (9) that presents information in a form that may be perceived by man (sound or image), or at an object being controlled (10), such as a metal-cutting machine tool with programmed control. For undistorted reproduction, the speed of motion of the carrier relative to the recording component (recording speed) must equal the speed of motion of the signal track relative to the reproducing element (reproduction speed). However, reproduction at a speed greater or less than the recording speed is sometimes specified. Such a method makes it possible to study a recorded process that has been slowed down or speeded up and to create special sound and other effects (such as those produced by slow-motion or speeded-up filming).
Carriers are divided into reversible and nonreversible types. Reversible carriers, such as magnetic carriers, permit complete or considerable erasure of information contained in the signal track (if it is no longer needed) and the use of the carrier for a new recording (multiple use). Nonreversible carriers, such as film or punched cards, do not permit repeated use for recording.
A distinguishing feature of most automatic recording units is the fact that the stored information is also reproduced automatically. The reproduced information is of the same nature as the original information—for example, sound signals recorded on magnetic tape or a phonograph record are reproduced as sound; an image is reproduced as an image. Mixed information recording and reproduction units, in which recording is nonautomatic but reproduction is automatic, and vice versa, also exist. The equipment used in telegraphy for recording by manual punching of holes in a paper tape (a perforator) is an example of the first type. The recording is subsequently reproduced automatically. Various recording devices and instruments are an example of the second type. Such devices record automatically but reproduce non-automatically, by means of visual examination of a signal track (beam storage tubes and electrochemical, spark, and ferrographic recording methods). A distinction is made between the concept of the method, or the technical devices used to perform fundamental processes (recording, reproduction, and erasure), and that of systems, or aggregates of various methods that have in common essential physical processes that lead to the fundamental processes.
Analog and digital recording methods are used. Analog recording is a method by means of which all values of an input signal may be recorded in a certain range. Analog recording, in turn, is divided into direct and modulated recording. In direct recording, the signals change according to permissible or anticipated distortions rather than undergo radical transformations in form. A sound recording is an example of a direct recording. In modulated recording, the signals are fundamentally transformed in the recording channel through modulation of some auxiliary oscillation (frequency-modulated, amplitude-modulated, and other types). The signals are demodulated in the reproduction channel. Modulation makes possible an increase in the precision of a recording by reducing the effect of interference; in some cases it is used to match the parameters of signals with the parameters of the information recording and reproduction channels. The reverse of an analog recording is the method of digital recording, in which input signals are quantized and are then converted into binary numbers for recording on a carrier as a code. Reconversion (decoding) occurs in the reproduction channel. Digital recording is used principally in computer memory banks.
Mechanical, photographic, and magnetic recording are the most widespread recording systems. Electrostatic and thermoplastic recording are less frequently used. All these systems of recording make possible the production of a large number of copies of the recording (printing) by means of processes unique to each system.
Information recording and reproduction units are used extensively in various fields of technology, including radio and television, in which they are used to prepare programs for broadcast; in communications technology, including space communications, for periodic accumulation and transmission of data; in computer technology, where they are among the most important functional components of any computer; in time-pattern process control; and in scientific research. The scientific development and technical improvement of recording and reproduction of information are designed to increase reliability (precision) and recording density, which is the amount of useful information per unit of length, surface, or volume of the carrier.
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