Code

Code is a system of symbols and rules used for expressing information according to an unvarying rule for replacing a piece of information from one system, such as a letter, word, or phrase, with an arbitrarily selected equivalent in another system. Substitution ciphers are similar to codes except that the rule for replacing the information is known only to the transmitter and the intended recipient of the information. Binary code and other machine languages used in digital computers are examples of codes. Elaborate commercial codes were developed during the early 20th century. In recent years more advanced codes have been developed to accommodate computer data and satellite communications.
Binary code is the code used in digital computers, based on a binary number system in which there are only two possible states, off and on, usually symbolized by 0 and 1. Whereas in a decimal system, which employs 10 digits, each digit position represents a power of 10 (100, 1,000, etc.), in a binary system each digit position represents a power of 2 (4, 8, 16, etc.). A binary code signal is a series of electrical pulses that represent numbers, characters, and operations to be performed. A device called a clock sends out regular pulses, and components such as transistors switch on (1) or off (0) to pass or block the pulses. In binary code, each decimal number (0–9) is represented by a set of four binary digits, or bits. The four fundamental arithmetic operations (addition, subtraction, multiplication, and division) can all be reduced to combinations of fundamental Boolean algebraic operations on binary numbers.
Numerical control is control of a system or device by direct input of data in the form of numbers, letters, symbols, words, or a combination of these forms. It is a principal element of computer-integrated manufacturing, particularly for controlling the operation of machine tools. NC is also essential to the operation of modern industrial robots. The two basic types of NC systems are point-to-point, in which a device is programmed to perform a series of motions with fixed starting and stopping points, and continuous-path, in which a point-to-point programmed device has sufficient memory to be “aware” of its former actions and their results and to act in accordance with this information.
Client –server architecture is the architecture of a computer network in which many clients (remote processors) request and receive service from a centralized server (host computer). Client computers provide an interface to allow a computer user to request services of the server and to display the results the server returns. Servers wait for requests to arrive from clients and then respond to them. Ideally, a server provides a standardized transparent interface to clients so that clients need not be aware of the specifics of the system (i.e., the hardware and software) that is providing the service. Today clients are often situated at workstations or on personal computers, while servers are located elsewhere on the network, usually on more powerful machines. This computing model is especially effective when clients and the server each have distinct tasks that they routinely perform. In hospital data processing, for example, a client computer can be running an application program for entering patient information while the server computer is running another program that manages the database in which the information is permanently stored. Many clients can access the server's information simultaneously, and, at the same time, a client computer can perform other tasks, such as sending e-mail. Because both client and server computers are considered intelligent devices, the client-server model is completely different from the old “mainframe” model, which utilized a centralized mainframe computer that performed all the tasks for its associated “dumb” terminals.