Central processing unit (CPU) :

The part of the computer which executes program instructions is known as the processor or central processing unit (CPU). CPU is over single electronic component like the microprocessor chip, within the system cabinet or system unit in a microcomputer. The system unit also includes memory chips, circuit boards ports and other components. A microcomputer system cabinet will also have hard disks, disk drives etc., but these are considered separate from the CPU. It is principal part of any digital computer system, usually composed of control unit, and arithmetic-logic unit, can say heart of the computer. It consider the physical heart of the entire computer system; to it is linked various peripheral equipment, including auxiliary storage units and input/output devices

• Control Unit is the essential part of a CPU or other device that directs its operation. The control unit command the rest of the computer system how to perform a program's instructions. It controls the movement of electronic signals amongst memory-which temporarily holds data, processed information and instructions -and the ALU. Also it directs these control signals between input/output devices and CPU. The control unit is the circuitry that controls the flow of information through the processor, and set coordinates between the activities of the other units within it. In a method, it is the "brain", as it controls what happening inside the processor, and in turn controls the rest of the PC.
• Arithmetic-Logic Unit typically called the ALU is a digital circuit that performs 2 types of operations -logical and arithmetic.  Arithmetic operations are the fundamental mathematical operations consisting of, subtraction, addition, and division and multiplication. Logical operations consist of comparisons operation. That is, 2 pieces of data are compared to see whether 1 is equal to, less than, or greater than the other. ALU is a basic building block of the   CPU of a computer. Memory: - Memory use in a computer to store, at least temporarily, programs and data. Memory-also known as the main storage or primary memory- it is a part of the microcomputer that holds data for processing, instructions for processing the data (the program) and information (processed data). Part of the contents of the memory is held only temporarily basic, that is, it is stored just till the microcomputer is turned on. When you turn off the machine, the contents are lost. The capacity of the memory to hold data and program instructions vary in different computers. The original IBM PC could only hold about 6, 40,000 characters of data or instructions. But in the modern microcomputers, one can store millions, even billions of characters in their memory.