The Central Processing Unit (CPU) is the part of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical and input/output operations of the system.
The CPU is also known as the brain of the computer. The speed of CPU depends upon the type of microprocessor used and it is measured in Mega Hertz (MHz).
The microprocessor is fabricated on a single IC (Integrated circuit). IC is a piece of silicon,
composed by thousands of transistors.
The first chip, Intel 4004, made by Intel in 1971 by scientist Ted Hoff and engineer Frederica Faggin.
Some of the popular microprocessors are i5. i3, Core 2 Dual Intel, Dual Core, Pentium IV, etc.
Two typical components of a CPU are the Arithmetic Logic Unit (ALU) and the Control Unit (CU):
Arithmetic Logic Unit
In computing, an Arithmetic Logic Unit (ALU) is a digital circuit that performs arithmetic and logical Operations. The ALU is a fundamental building block of the central processing unit of a computer.
An ALU loads data from input registers and control unit tells the ALU that which operation is to be performed on that data and then the ALU stores its result into an output register.
Most ALUs can perform the following operations:
(1) Logical operations (AND, NOT, OR, XOR)
(ii) Arithmetic operations (addition, subtraction, multiplication and division).
(iii) Bit-shifting operations (shifting or rotating a word by a specified number of bits to the left or right, with or without sign extension).
(iv) Comparison operations (=, <, <=, >, >=)
The control unit coordinates the input and output devices of a computer system. It fetches the instructions which are given in the form of microp rograms. It directs the operation of the other units by providing timing and control signals.
In general, a control unit is a central part of the machinery that controls its operation and entire processing.
e.g. in the automobile industry, the control unit helps to maintain various functions of a motor vehicle.
The control unit is the circuit that controls the flow of data through the processor and coordinates the activities of the other units within it. Control unit acts like human nerves system, which does not process data but behaves as a central unit for other data manipulating components.
It is the internal part of CPU. These are used to store intermediate results obtained during the execution of instruction.
This unit is responsible to store programs or data on a temporary or permanent basis. It has primary memory (main memory) and secondary memory (auxiliary memory). The input data which is to be processed is brought into main memory before processing.
The needed instruction for processing and any kind of intermediate results are also stored in primary memory. Together with these, the final output is also stored in primary memory before transferring it to the output unit. Another kind of memory is referred as secondary memory of a computer system. This unit is used to permanently store data, programs and output. This unit does not deal directly with CPU.
An input device is a hardware device that sends data intO the computer system. These devices are used to input (or enter) data and instructions into the computer system. All instructions are accepted by the CPU through electrical pulses from various kinds of input devices.
Some of the input devices are explained as follows:
It is the most commonly used input device which uses an arrangement of buttons and keys to. Both data and program, can be entered into the computer through the keyboard. It is an essential device for interactive processing because the user can easily issue commands to receive the data response immediately on the computer screen.
Types of Keys on Keyboard
(i) Alphanumeric keys All of the letters and numbers on the keyboard are A-Z and 0-9.
(ii) Punctuation keys Such as comma, period, semicolon, brackets, parenthesis and so on.
(iii) Special keys Such as Control keys, Arrow keys, Caps lock key, Delete key, Alt key, Shift key etc.
(iv) Function keys Keys labeled Fl to F12.
These keys have different meaning depends on running program.
A pointing device is used to communicate with the computer by pointing to the locations on the monitor. It can also be used for:
- sending command signals to the computer.
- selecting items on the screen.
- selecting commands from commands menu.
- drawing graphics, sketches, etc.
Some commonly used pointing device are mouse, trackball, joystick, lightpen, graphics tablet, touch screen and touch pad.
The mouse is a pointing device that allows to control the movement of pointer (also known as mouse pointer) on screen. Mouse performs various functions by detecting two-dimensional motion relatively to its supporting surface. A mouse can be of different types like wired, I wireless mouse, optical mouse, mechanical mouse etc. Generally a mouse have two buttons — a right button and left button.
Mouse also include a scroll wheel between the buttons to scroll down the application window and their contents also.
Different types of mouse are:
(a) Mechanical Mouse In this type of mouse, movement of a cursor on the screen is — relative to the movement of the ball available at the bottom of the mouse.
(b) Optical Mouse It uses a Light EmItting Diode(LED) and Photodiodes to detect movement.
(c) Laser Mouse It uses Infrared Laser Diode instead of a normal LED.
(d) Wireless Mouse It communicates with the computer via Radio waves (often using Bluetooth hardware and software) so that a cord is not needed (but such mouse needs internal batteries). A mouse also includes one or more buttons (and possibly a scroll wheel) to allow users to interact with the GUI.