People use Input devices to enter data into computers. One of the most common input devices is the computer terminal, which looks like a typewriter keyboard combined with a television screen. Data that are typed on the keyboard appear on the
screen. At the same time, the data go to the memory. The memory also stores a program - the step by -step series of instructions for the computer to follow. The processor manipulate the data according to the program.
The processed information is sent to an output devices, which presents it to the computer user. In many cases, the computer terminal that served as the input device also acts as the output device, and it screen displays the results. Printers are another important kind of output devices. File storage devices are used to save information and programs for the future use.
All data handled by computers, including words, enter the processor in the form of digits. Computers commonly use the digits of the binary numeration system ( see numeration systems (the binary system). Unlike the familiar decimal system, which used 10 digits, the binary system uses only two digits :0 and 1. These digits are called bits. Different combinations of bits represent letters, symbols and decimal numerals. Each such combination of bits is called byte. For example, according to one standard code, the binary representation for the letter A is 100 001, while the binary representation for the letter Z is 101 1010. Each symbol and decimal numeral also is represented by a specific combination of 0's and 1's
Each of a computer's thousands of tiny electronic circuits operates much like an ordinary light switch. When a circuit is off, it corresponds to the binary digits 0. When a circuit is on, it corresponds to the digit 1. Binary digits, like decimal numbers, can be added, subtracted, multiplied and divided. Thus, a computer can perform all the basic arithmetic operations.
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