Digital system have such a prominent role in everyday life that we rever to the present technological period as the digital age. Digital system are used in communication, business transactions, traffic control, space guidance, medical treathment, weather monitoring, the internet, and many other commercial, industrial, and sciencetific enterprices. We have digital telephone, digital television, digital versatile dises, digital cameras, handled devices, and of course, digital computer. The most striking property of digital computer its generality. It can follow a sequence of instructions called a program, that operates on given data. The user can specify and change the program or the data according to the specific need. Because of this flexibility, general purpose digital computers can perform a variety of information processing tasks that range ovr wide spectrum of application.
One characteristic of digital system is their ability to represent and manipulate discrete elements of information. Any set that is restricted to a finite numberof element contains discrete information. Examples of discrete sets are the 10 decimal digits, the 26 letters of the alphabet, the 52 playing card, and the 64 squares of a chessboard. Early digital computer were used for numeric computations. In this case, the discrete were the digits. From this applications, the term digital computer emerged. Discrete elements of informations are represented in a digital system by physical quantities called signals. Electrical signals such as voltage and currents are the most common. Electronic devices called transistors predominate inthe circuitry that implement these signals. The signals in most present day electronic digital system use just two discrete values and are therefore said to be binary. A binary digit, called a bit, has two values: 0 and 1. Discrete element of information are represented with groups of bits called binary codes. For example, the decimal digit 0 through 9 are represented in a digital system with code of four bits. Through various techniques groups of bits can be made to represent discrete symbols, which are then used the develop the system in a digital format. Thus, a dgital system that manipulates discrete element of information represented internally in binary form.
Discrete quantities of information either emerge from the nature of the data being processed or may be quantized from the continous process. On the other hand, the payroll schedule is an inherently discrete process that contains employee names, social security numbers, weekly salaries, income taxes and so on. An employee’s paycheck is processed by means of discrete data values such as letter of alphabet (names), digits (salary), and special symbols(such as $). On the other hand, a research scientist may observe a continous process, but record only specific quantities in tabular form. The scientist is thus quantizing continous data, making each number in his or her table a discrete quantity. In many cases, the quantization of a process ca be perform automatically by an analog to digital converter.
The general purpose digital computer is the best known example of a digital system. The major parts of a computer are a memory unit, a central processing unit, and input output units. The memory unit stores program as well as input, output, and intermediet data. The central processing unit performs arithmetic and other data processing operation as specified by the program. The program and data prepared by a user are transferred into memory by means of an input device such as keyboard. An output device, such as a printer, receives the results of the computations, and the printed results are presented to the user. A digital computer can accommodate many input and output devices. One very useful device is a communication unit that provides interaction with other users through the internet. A digital computer is a powerful instrument that can perform not only arithmetic computations, but also logical operations. In addition, it can be programmed to make decisions based on internal and external conditions.
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