INTRODUCTION TO PC

Computer is the most powerful tool man has ever created. Computers are used in almost every working place in the modern times that is school, colleges, offices, railways, banks, industries, hospitals etc. The word “computer” comes from the word “compute” which means to calculate. So a computer can be considered as a calculating device that can perform arithmetic operations at a high speed but more accurately.

Computer is a digital electronic storage device, which accepts data and set of instructions, manipulates it, and retrieves the information at very high speed. In other wards we can say that a computer is a data processing device which following specific instructions, perform a sequence of operations to achieve a desired result. In this unit we will discuss about personal computer (PC) and its components. From here onward, the words PC and computer are used interchangeably.

The word “computer” comes from the word “compute” which means to calculate. So a computer can be considered as a calculating device that can perform arithmetic operations at a high speed but more accurately.

Every Computer has the general structure shown in this Figure

A computer receives input (data or/and instructions) through the input devices (such as keyboard or mouse), process the data according to the specified instructions (via CPU) and then presents the output (results) in a readable form on its output device, i.e., either on its screen/monitor or on paper through the printer attached to it.

A computer consists of a Central Processing Unit (CPU), memory and various devices which can be categorized as Input/Output Devices. Information is communicated between these separate units by the Systems Bus.

The Central Processing Unit (CPU) performs the actual processing of data. The data it processes is obtained, via the system bus, from the main memory. Results from the CPU are then sent back to main memory via the system bus.

In addition to computation the CPU controls and co-ordinates the operation of the other major components. The CPU has two main components, namely: Control Unit (CU) and an Arithmetic/Logic Unit (ALU).

The Control Unit : controls the fetching of instructions from the main memory and the subsequent execution of these instructions. The control unit also controls the operation of the peripheral devices (keyboard, monitor or printers etc.) and the transfer of information between the units that make up the computer.

The Arithmetic/Logical Unit (ALU): carries out arithmetic operations on integer (whole number) and real (with a decimal point) operands. It can also perform simple logical tests for equality and greater than and less than between operand.

The memory of the computer is split into main memory and external (secondary/auxiliary) memory.

Main memory is fast and limited in capacity. The CPU can only directly access information in main memory. Main memory cannot retain information when the computer is switched of. Main memory consists of a series of numbered locations called bytes, each byte equals eight bits.

Secondary memory is slow and virtually unlimited in capacity information remain in it, even when the computer is switched off.

Information on external memory cannot directly access by the CPU. The information stored on external memory is first transferred to main memory, and then can be accessed by the CPU.

The internal representation of information in the computer and on external memory is in terms of the Binary system using only the basic symbols 0 and 1.

Programs to be executed by the computer are placed in main memory and the CPU fetches each instruction in turn from memory and executes it.

The memory unit that directly communicated with the CPU is called the primary memory or main memory

There are two types of computer (main) memory inside the computer i.e., RAM (Volatile) and ROM (Non-volatile).

ROM chips are supplied by computer manufacturer and it is not possible for a user to modify the programs stored inside the ROM chip. However, in case of PROM (non-volatile), it is possible for a user to customize a system by storing own program in a PROM chip.

The basic difference between PROM and a ROM is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process.

Once the information is stored in a ROM chip or a PROM chip it cannot be changed. However, there is another type of memory chip called Erasable Programmable Read-Only Memory (EPROM) that overcomes this problem.

Secondary memory (Auxiliary memory) provides a place where data can be permanently stored and transferred to and from main memory (RAM). Such as Hard Disk, Floppy Disk, Pen Drive, CD-ROM, DVD, Zip-Drive, magnetic tape.

Input devices (such as keyboard, mouse, joystick etc.) are used to enter data into primary storage (or primary memory) or a hardware device that sends information into the CPU.

The output generated by a computer can be transmitted to the user via some devices or media. These devices are called output devices such as monitor, printer etc.