مقدمة .. الحاسبات تعمل - جون كلارك

Introduction .. Computers work - John Clark

The computer industry is considered one of the most important and fastest growing modern technological industries, as it started from the testing phase in the early fifties and has spread to various fields today, from scientific, technological, industrial, commercial and even our daily life affairs, and its spread has become a standard for progress among nations.

Electronic computers are of two types, analog computers and digital computers. Analog computers are those in which electrical signals are continuous in time and their intensity is proportional to the amounts of the natural measurements that they represent, such as speed, force, mass, etc. The analog computer consists of a group of electronic circuits, each of which has a specific function, connected in a specific way to simulate, from a mathematical point of view, the problem to be solved. The computer processes the incoming signals, so the outgoing signals are the required answer. The analog computer has lost much of its importance due to the prevalence of the digital computer, and its use at the present time is limited to a few special cases.
In a digital computer, electrical signals are binary, meaning that they range between two specific limits. Since these two limits are fixed in a water circuit, the amounts of natural measurements are represented not by the intensity of the binary signals, but by their sequence or arrangement according to a specific convention or code. The heart of a digital computer is a group of electronic circuits known as the main processor, consisting of a mathematical and logical unit that performs a limited number of simple arithmetic and logical operations, such as addition, for example. From a unit that controls the mathematical and logical unit, the control unit receives instructions in the form of binary signals, and translates these instructions into a series of operations performed by the mathematical and logical unit. If the digital computer is to perform any complex operation, this operation is divided into a group of instructions that the control unit understands and which can then be executed by the mathematical and logical unit. This group of instructions is known as the program.

The program to be executed, as well as any numerical or non-numerical data related to this program, is stored in the form of binary signals in a set of electronic circuits known as the computer's main memory. One of the important characteristics of a digital computer is that the program can be prepared so that what is executed depends on the results of executing other instructions in the program. The main memory may be supported by other storage devices known as cumulative stores, such as magnetic disks, magnetic tapes, paper tapes, etc.

Since the main processor and the memory work with three-way signals, while the information required to be entered into the computer and the expected results from it are not usually in this form, input and output devices are used to facilitate communication with the computer, and these devices differ according to the situation for which the computer is prepared, as will be mentioned later.

The digital computer is characterized by its extreme accuracy, high speed and high degree of reliability, which qualifies it to perform extremely complex calculations. The digital computer executes in a few seconds without error what might require several months of arduous work from the human worker. This is what opened up horizons for the digital computer that were, until a few years ago, closer to dream descriptions. However, the digital computer remains, despite all that it can accomplish, just a flexible tool that accurately and faithfully executes the instructions issued to it.

Computer equipment (A), magnetic tape unit for storing information (B), data entry touch panel (C), paper tape reader and printer (D).