Anatomy of Digital computer
The two main characteristics of a computer are: (i) it responds to a specific set of instructions in a well-defined manner. (ii) It can execute a pre-recorded list of instructions (a program). Modern computers are electronic and digital. The actual machinery such as wires, transistors and circuits is called hardware and the instructions and data are called software.
The major components of a computer are listed below:
CPU: The CPU has two parts i.e. Control Unit (CU) and Arithmetic Logic Unit (ALU). CPU is called the brain of computer as it executes program instructions.
Control unit: The control unit tells the rest of the computer system how to carry out a program’s instructions. It directs the movement of electronic signals between memory -which temporarily holds data, instructions and processes information - and the ALU. It also directs these control signals between the CPU and input/output devices.
ALU: ALU performs two types of operations - arithmetical and logical. Arithmetical operations are the fundamental mathematical operations consisting of addition, subtraction, multiplication and division. Logical operations consist of comparisons. That is two pieces of data are compared to see whether one is equal to, less than, or greater than the other.
Memory: Computer memory is the working storage area in computer. There are two kinds of computer memory: primary and secondary.
Primary memory: Primary memory is accessible directly by the processing unit. RAM, ROM is the example of primary memory. The contents of the primary memory are lost as soon as the computer is switched off. Primary memory is more expensive than secondary memory.
Secondary Memory: Secondary memory such as floppy disk, magnetic disk, etc., is located outside the computer. The additional memory is required in all the computer systems to store hundreds of millions of bytes of data for the CPU to process. This memory is called auxiliary memory or secondary storage.
Input device: Input devices convert input data and instructions into binary form for acceptance by the computer. The different types of input devices are keyboard, Optical Character Recognition (OCR), Magnetic Ink Character Recognition (MICR), mark sense reader, etc.
Output device: Output devices are the devices that receive information from the CPU and present it to the user in the desired form. Output devices include display screen, loudspeakers, printers, plotters, etc.
Secondary storage: Secondary storage such as floppy disk, magnetic disk, etc., is located outside the computer. The additional memory is required in all the computer systems to store hundreds of millions of bytes of data for the CPU to process. This memory is called auxiliary memory or secondary storage. In this type of memory the cost per bit of storage is low. However, the operating speed is slower than that of the primary memory. Huge volume of data are stored here on permanent basis and transferred to the primary storage as and when required. Most widely used secondary storage devices are magnetic tapes, magnetic disks and floppy disks.