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Essay on “Storage System in Digital Computer” Complete Essay for Class 10, Class 12 and Graduation and other classes.

Storage System in Digital Computer

There are secondary storage devices in a computer which constitute a basic part of the digital systems’ peripheral equipment. They can store much larger amounts of Information than can a main memory, but operate at slower speeds. The most common forms of secondary storage are magnetic tape and disk. Other systems include the magnetic bubble memory and the optical disk memory.

Magnetic tape was introduced as a data-storage medium in 1951. For about the next decade, almost all digital computers used magnetic tape for secondary storage, but by the mid-1960s, magnetic disk and drum devices arrived to augment the tape units in mainframe systems designed for scientific and business data-processing applications, that required rapid retrieval of stored data and programs. The main use of magnetic tape today is for archive and bulk information transfer from one machine to another. With home computers, it is used in audio tape-cassette recorders to provide low-cost auxiliary storage.

Magnetic disk technology was applied to secondary data storage in 1962. A magnetic disk is a flat, circular, metal or plastic plate coated on both sides with iron oxide or other readily magnetisable material. Input signals are recorded on the surface of the disk as magnetic patterns in circular tracks, by a recording head while the disk is rotated by a drive unit. The heads, which are also used to read the magnetic impressions on the disk, can be positioned anywhere on the disk with great precision. A collection of disks (often 11 in number), called a disk pack„ is mounted vertically on the spindle of a drive unit, which is equipped with multiple reading/writing heads. A single disk pack may hold as many as 300,000,000 bytes. Magnetic disk devices have a distinct advantage over tape units. They can directly access a block of data on a precise track without having to pass over a major portion of its contents sequentially, thereby reducing retrieval time to a fraction of a second. Small, flexible plastic disks, commonly called floppy disks, information re developed in the 1970s. Floppy disks cannot store as much n formation or retrieve data as rapidly as conventional rigid disks, but they are adequate for use with personal microcomputers, where low cost and ease of use are often of primary consideration.

 The optical disk mass-storage system, introduced during the early 1980s, developed from videodisc technology. The most sophisticated system of this kind can store up to 4000,000,000 bytes, far more than the highest capacity magnetic disk units. Information, encoded by a laser beam on the metallic recording medium of a videodisc platter, as a pattern of pits.

 For information retrieval, the digitally coded data are tracked by an optical laser scanner.

The operations of a digital computer system are regulated and integrated by a central control unit and, in some cases, several subordinate control elements. The central control unit constitutes a principal component of the CPU. It selects and calls up program -instructions from the memory in proper sequence, and interprets them so as to direct the movement of data through the system for processing and output.

 In a certain sense, the operation of a control unit is analogous to that of a miniature but complete computer whose output signals run the other parts of the system. In effect, each computer instruction is broken into a sequence of small operations known as micro steps for microinstructions. The micro programmed machine has a pleasing simplicity in its structure and is relatively straightforward to understand, build, and extend.

All data in the main memory are transferred to the arithmetic logic unit for processing, which involves basic arithmetic functions and certain logic operations. The latter includes the com-paring of data and the selection of changes to the normal instruction sequencing.

The ALU consists of two basic components: registers and operational circuits. The registers are storage elements that temporarily hold binary digits representing the data being processed. They are composed of flip-flops, circuits capable of assuming either of two stable states representing 0 and 1. The operational circuits include such binary logic coincidence circuits as the AND gate, OR gate, NAND gate, NOR gate, and inverter. These elementary gates are combined in various arrangements to perform the arithmetic and logic operations.

Wide arrays of devices, some of which can also be employed to input information, convert electrical signals from the ALU into a form usable by a human operator, or a machine controlled by the computer.

The most common output devices include video displays, high-Speed printers, and console typewriters. A recent development in our equipment is an audio response’ unit that can convert data into spoken messages. Some of these units construct sentences with human speakers’ words that have been digitalized and stored in a memory device. Others synthesize human speech, providing the appropriate response by generating signals similar to those produced in regular speech.

As has been indicated, the power of the digital computer rests not only. on its speed and capacity for manipulating large quantities of coded data but also on its ability to perform complicated sequences of such actions under control of stored program. This permits the same computer to work at a variety of tasks in sequence, or even intermittently. Before the computer can work at all, however, a program or programs must be prepared in some suitable programming language and introduced into the computer’s memory, to instruct the computer exactly what to do. A computer task is first formulated and then expressed in an appropriate language, presumably one suited to the application and the thought processes of the formulator. The specification thus expressed, is then translated, perhaps in several stages, into a coded program directly executable by the computer on which the task is to be run. The coded program is said to be in “machine code”, or “machine language”, while languages suitable for original formulation are referred to as “problem-oriented languages”, or “high-level languages”.

Computer systems are supplied with a variety of programs designed largely to assist the user to run jobs, or to optimize system performance without unduly penalizing the user running jobs. This collection of programs constituting the operating system is as important to the operation of the computer system as the hardware itself. The operating system is usually supplied by the computer manufacturer, or a firm specializing in program design. Successful operation of a computer system depends on the stable and reliable function of its operating system, which is usually “frozen” and not subject to changes, even to improve performance, until the implications for operation have been first explored. Current technology makes it possible to build some operating characteristics into a processor at the time of manufacture, in the form of fixed programs introduced by customer orders. This leads to a further distinguishing feature known as firmware.

 During normal operation, the operating system is in general, over-all control while user programs are being executed. It decides when a particular program should be run and what to do when a certain process terminates (subject to the ultimate control human operators). In most cases, various utility programs that operate as independent units to facilitate the programming process are also available within the system. In this category are translators’ which transform an entire program from one language to another: interpreters, which execute a program sequentially, translating at each step; editors, which allow text files to be entered or altered or debuggers, which execute a program piecemeal, interpretative or not, and monitor various circumstances to permit the program to check to see whether the operation of the program is correct.


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