Computer Basics

Computer: A computer is a device that computes or calculates numbers. A computer, however, does more than that. It can edit text, generate pictures or graphs, make animation, translate language and even play games or drive motorcars etc.

Computer System: A system is a set of components that works together to accomplish one or more common goals. A computer system can be said to be a system of three major components.

A. Computer hardware: It includes all mechanical, electrical or electronic parts or components of the computer.
B. Computer software: This includes operating system, programmes or applications that instruct a computer how to process the data and generate required information.
C. Computer personnel: People who prepare data for computerized input write computer programmes, monitor computer operations and distribute the output. There are also end users who use computer resources.

Functional Components:
The hardware of a computer system can be classified into the Central Processing Unit (CPU) and peripherals.
The heart of the computer is called CPU or Processor.
The CPU performs:
i) Arithmetic Operations
ii) Logical Operations
iii) Input-Output Operations
iv) Internal data movements (moving data between various parts of storage)
v) Data manipulation
To perform these operations the CPU has various components:

a. Arithmetic-Logic Unit (ALU): It performs the actual calculations (addition, subtraction, division, multiplication) and comparison (equal to, greater, lesser, positive, negative, zero etc).
b. Control Unit (CU): It coordinates the operation of the hardware, the flow and execution of data and instructions that are fed into the memory or main storage via the CPU.
c. Memory Unit (Main Store): It holds data instructions (that are being interpreted and executed), intermediate results and final results ready for output. The data and instructions are passed from the main store into ALU, or to and from the storage devices under the control of the CU.
Within the CPU there are a number of high speeds, special purpose memory units called registers. These registers carry out critical functions in the execution of programmes. A computer has four basic types of registers:
1) Accumulator register (ACC)
2) Store operand register (SOR)
3) Control register (CR)
4) Instruction address register (IAR).

Buses: The control unit and internal storage are linked together by sets of parallel electrical conducting lines called buses. The buses that carry data are called data buses. The retrieval of data from memory is carried by the memory address bus.
Peripheral Devices:
The peripheral devices can be classified as input devices, output devices and backing storage devices.
Input devices allow the user to get data into the machine. A large range of input, devices are available, e.g. keyboard, mouse.
Output devices are peripherals used to output results to the user. They include printers, plotters and VDUs (Visual Display Units).
Backing storage devices or the secondary storage devices are mainly hard disk, CDS, disk packs, floppy disks, and tapes used to store data and programmes permanently.

Types of computers:
On the basis of their use computers can be classified as:
a) Analog Computers: Analog computers are computers that measure physical quantities (i.e. pressure, temperature, length etc.) and convert them to numeric values. Analog computers are used mainly for scientific and engineering purposes.

b) Digital Computers: Most computers are digital devices, i.e. they count the numbers- -(or digits) that represent numerals, letters, or other special symbols. Special purpose digital computers can be fixed permanently in the machine e.g. processors that are installed in automobiles to control fuel, breaking systems etc.

c) Hybrid Computers: The features of analog and digital machines are combined to create a hybrid computing system. For example analog devices measure a patient's vital signs like temperature, heart functions. These are then converted to numbers and supplied to the digital components that monitor the patient's vital signs. Any fluctuation can thus be noticed immediately.

On the basis of their size computers can be classified as:
i) Micro Computers: It is the smallest type of computer. Inside a Micro computer, the ALU and CU are combined on a single chip called microprocessor. Micro computers contain two types of memory:
A. Random Access Memory (RAM): Where programmes and data are held temporarily during processing. Data stored in RAM is lost when the machine is switched off.
B. Read Only Memory (ROM): Where permanent instructions of data are held. The ROM does not require a continuous supply of power to retain its contents.
Micro computers are used as home computer or by small businessmen or individual professional where volumes of data processing and speed requirements are small. These are also extensively used for computer graphics, Computer Aided Design (CAD) and Computer Assisted Manufacturing (CAM) applications.

Personal Computers (PC): These have slightly better capabilities and are used generally for business applications. These are single user system. Currently IBM PC in, various configurations and IBM - PC compatibles are the most popular small computers.

Mini Computers: Mini computers are more powerful than the micro computers and can support several users. They have larger RAM and backing storage capacity and can process data more quickly. They are basically used for process control systems.

Main frame computers: Main frames are very large computers with very high capacity of main store. They can process large amounts of data very quickly. So they are used by banks, big companies and Govt. departments as their main computer. These can be linked into a network with smaller departmental computers, micro computers or with each other.

Super Computers: Complex scientific applications like weather forecasting require a large amount of data to be manipulated within a very short time. Large super computers with faster processing using multiple processors and superior technology are use for complex tasks requiring a lot of computational power.

The traditional design of a single processor handling data and instructions in a single stream is called the "Von Neumann designs". They typically have multiple ALUs. Each ALU is specialized for a particular operation, and all capable of performing simultaneous or "Parallel" processing of different tasks. Control is maintained at several points, with an overall controller in charge.

Input & output devices:
These are the devices which form an essential link between the user of computer system and computer system itself. There devices from instance between user and the system.
Input devices are used to get raw data into the computer and an output device gives output of the processed information.
The following are the main input devices:
a) Keyboards: The key board resembles a typewriter. But there are additional keys that handle control functions. The computer keyboard has three categories of keys.
- Alphanumeric keys
- Special key
- Function keys
The Alphanumeric Keys comprises of alphabets (A-Z or a-z), numbers (0-9) and other characters, like space, ./ × ' ; : — ~ ! @ # $ % ^ & * ( ) - + = | \ { } [ ].

The Special Keys perform specific tasks. Some of the special keys are, Enter or the Return key, Backspace key, Del key, the Ins key, Shift keys, e Caps lock key, Num Lock key, Ctrl key and the Alt key.

The Function Keys are used to perform a set of operations by a single keystroke. The function keys can be used for various functions. They can be used as short hand for a sequence of keystrokes, configured accordingly.

Mouse: One of the most popular types of specialized input devices for terminals or micro computers is a mouse. Which is used as a pointing device, the mouse is a small box, about the size of a tape cassette with a round ball on the bottom and one or more buttons on the top. The mouse is attached to a terminal or micro computer by a cable. A mouse enables the user to manipulate a pointer or an arrow on a terminal or micro computer screen.

Joystick: Joysticks are designed in the shape of handles that swivel in 360 degree arcs, enabling their users to control screen figures.
Its utilization for commercial data processing applications is limited.

Barcode reader: Data can be coded in the form of light and dark bars with coded spacing and thickness. These are called barcodes which are commonly used to identify items. Each item is labeled with a Universal Product Code (UPC). The code is read by a wand or pen which transmits a laser beam and receives the reflection from the label. These pulses are compared with standard codes stored in the computer. A barcode is commonly seen on the back of any book published in recent times.

OMR: The Optical Mark Reader (OMR) is a device which can detect the presence or absence of a mark on a paper. Light is incident onto the paper and the reflected light is detected. The presence of a mark is detected due to intensity of light being reflected from the mark. OMR is used in reading answer sheets, questionnaires.

OCR: Optical Character Reader (OCR) is an improvement over OMR. This can not. only detect a mark but can also recognize its shape and identify characters directly from source documents. The amount of light reflected differs depending on the shape of the character and the OCR can detect and interpret these minor differences.
MICR: Magnetic Ink Character Recognition (MICR) systems use special ink which can be magnetized, to print characters that can then be read and decoded by special magnetic devices.

This system is widely used by banks for processing cheques. The cheque number, the bank and branch code and the account number are printed with ink containing magnetisable particles of iron oxide