A digital computer may be divided into the following fundamentals units:
1) Input Devices,
2) Output devices,
3) Peripherals (C.P.U. Storage devices, etc)
User gives instructions and command to the computer in the form of signals through input devices and the signals are recieved by C.P.U which has three Parts;
a) A.L.U b) C.U c) M.U
Input: The Input devices read the necessary data into the machine. In most General-purpose computers, the instructions that constitute the program must be read into the machine along with all the data to be used in the computations. Some of the more common input devices are Keyboard, punched-card and punched paper-tape readers, magnetic-tape readers and various manual input devices such as toggle switches and push buttons.
Control: The control section of a computer sequences the operation of the computer, controlling the actions of all other units. The control circuitry interprets the instructions which constitute the program and then directs the rest of the machine in its operation.
Memory: The memory, or storage, section of the computer consists of the devices used to store the information that will be used during the computations The memory section of the computer is also used to hold both intermediate and final results as the computer proceeds through the program memory devices are constructed so that it is possible for the control unit to contain any information in the memory. The time required to obtain information may vary some what, how-ever, and is determined by the type of device used to store the information Common storage devices are integrated-circuit memories, magnetic tape, and magnetic disks.
Arithmetic Logic Unit: The arithmetic logic units of most computers are capable of performing addition, subtraction, division, and multiplications as well as some "logical operations" which are described later. The control unit tells the Arithmetic Logic Unit which operation to perform and then sees that the necessary numbers are supplied the arithmetic element can be compared to the calculating machines described previously in that the numbers to be used are inserted, and it is then directed to perform the necessary operations.
Output: The output devices are used to record the results obtained by the computer and present them to the outside world. Most output devices are directed by the control element, which also causes the necessary information to be supplied to them common output devices are CRT displays, printers, card-punching machines, and magnetic tape drives. There are also many other types of output devices, such as lights, buzzers, and loudspeakers.
Arithmetical and logical unit does the processing on the data and instructions given by user. Control unit the flow of signals within the computer. It recieves the signals from input devices, gives it to ALU to perform processing and memory unit to store. It also give the processed information to output units. Memory unit stores the information. primary memory can be accessed directly by the processor whereas secondary memory can be used through primary memory. Output devices are used to display or print the output(processed information).