Classification of computers

According to the technology used, computers can be classified as
1. Digital Computers
2. Analog Computers
3. Hybrid Computers

Digital Computers are the most common computers being used like calculators, digital watches etc. They store data and instructions in the form of binary digits i.e. 0 and 1. These digits are used to denote letters, numerals and symbols.

Analog Computers measure continuous variations in devices like speedometer, thermometer, voltmeter, ammeter etc. (Analog means continuous variation).

Hybrid Computers are the combination of both Digital and Analog Computers. They measure analog quantities and convert them into digital signals for analysis. They can be used in space research and satellites. Computer with multimedia, robot etc. are examples of Hybrid Computers.

Computers can also be classified according to size and storage capacity as

1. Micro Computers
2. Mini Computers
3. Main Frame Computers
4. Super Computers

Micro Computers are small computers used as personal computers, computer notebooks, palmtop, laptop etc. for entertainment, education etc, at home or at office where volume of data is less.

A Mini Computer is a multi user system. It can be used by many users simultaneously. Mini Computers have larger RAM (Random Access Memory) and storage capacity. They can process data more quickly. Reservation system, banking system, etc. are using Mini Computers.


Main Frame Computers are large and powerful. They are used for complex calculations. They can support many input and output devices. They can process large amount of data quickly. They have a high storage capacity.


Super Computers are the largest, fastest, and most expensive computers used in the fields of medicines, industries, space research etc.They have many processing units working simultaneously to perform billions of operations every second.

COMPUTER VIRUS

• Computer virus are programs that spread across computers by attaching a copy of itself to the files on the infected computer.
• When the infected file is run, the virus gets into action.
• A virus is usually harmful and can corrupt data, overwrite files, or use up system resources, and slow it down in the process.
• Some may be merely disturbing like sending email using address book.
• Viruses are written by programmers to cause trouble.

Computer Memory (RAM, ROM, PROM, EPROM, floppy disk, CD ROM, CD writer, DVD, Hard disk, pen drive)

The computer stores the data in an area known as memory. It can be compared to thousands of registers and files maintained in an office. The computer stores data in the forms of binary digits (0s and 1s) or Bits. The units are

• 8 Bits :1Byte
  1024 Bytes :1Kilo Byte (KB)
  1024 KB :1 Mega Byte (MB)
  1024 MB :1 Giga Byte (GB)
  1024 GB :1 Tera Byte (TB)

Memory can be classified into two types, namely

• Primary Memory
• Secondary Memory

PRIMARY MEMORY
Primary Memory or Main Memory is used to hold the program being executed and any other data currently in use. It is of two types namely:

Random Access Memory (RAM). Random access memory is Volatile Memory. It is also called Read/Write Memory. When the computer is switched off, information stored on the RAM is lost. Hence it is also known as Volatile Memory.

Read Only Memory (ROM). There are certain functions that the computer must perform when it is switched on. For example, connections have to be established within the various components if the computer and its peripherals. A series of programs are required to perform these functions. These programs are hardwired into the ROM Chips at the time of manufacture. ROM is non-volatile. When the computer is switched off, the data on these chips is not lost. Hence it is known as Non Volatile memory.

Programmable Read Only Memory (PROM). A variation of the ROM chip is PROM. PROM can be programmed to record information using a facility known as PROM Programmer. If the chip is programmed, the recorded information cannot be changed and PROM becomes ROM. This is also Non-volatile.

Erasable Programmable Read Only Memory (EPROM). Information in these chips can be erased by exposing them to ultra-violet rays. The chip can then be programmed afresh to record different information.


SECONDARY MEMORY

Secondary Memory or Auxiliary Memory is the area in which the processed data or information can be stored. The devices used are known as secondary storage devices.

Floppy Disk. It is a flexible plastic disk coated with a thin layer of Iron Oxide. They are available in three sizes viz. 31/2, 51/4 and 8 inches. The commonly used is the 31/2” floppy disk. The storage capacity of these disks is limited (1.44 MB).

CD ROM. CD ROM (Compact disk- Read Only Memory) has larger storage capacity. However to transfer information from your computer to the CD, you require a device known as a CD Writer. The CD can hold data amounting to 700 MB. A more advanced version is the DVD which can hold data anywhere between 1 GB and 16 GB.

Hard Disk. The Hard Disk is another storage device, which is fitted to the computer so that the processed data can be stored and accessed easily. The software required to run the computer and any additional software or programs are stored in the hard disk. The new version computers are equipped with 40, 80 or 160 Giga Bytes Hard disk.


Pen Drive. It is a small, dust proof, shock proof, very light weight storage device, used to transfer files between USB compatible systems conveniently. It is available in a range of capacities even up to 8 GB or more.

Input and output devices of a computer

The devices that help the user to communicate with the computer are input devices. Once the data is fed into the computer, it works on the data, processes it and provides the results to the user. The devices that help the user to get the output from the computer are output devices.

Input devices
Input devices are those devices that are used to feed data and programs into a computer.

• Keyboard: the keyboard of a computer resembles a typewriter with a few additional keys to handle various functions. A computer keyboard has three categories of keys:
  Alphanumeric keys: Alphabets, numbers, characters.
  Special keys: enter, backspace, Del, esc, Ctrl, alt.
  Function keys: (f1 to f 12) for selected operations.
• Mouse: the mouse is one of the most popular input devices. This device helps you to manipulate a pointer or an arrow on the screen. The pointer moves according to the movement of the mouse on a flat surface.
• Light pen: helps in identifying bar codes.
• Scanner: scans documents and photos and transmits them to the computer.
• Microphone: helps to record sounds to the computer and extensively used to talk through the internet.
• Web camera: Also called webcam is a small low resolution digital video camera. Web accessible cameras upload images to a web server.
• Joystick: used mainly to play games.

Output devices
These are the devices that are useful in receiving information or processed data from the computer. Some of the commonly used output devices are

• Visual display unit: the unit that resembles a TV screen and commonly referred to as ‘Monitor’. This unit informs us about the activities performed by the computer.
• Printers: printers are the primary output device used to prepare permanent documents. The printers that are widely used are Dot Matrix, LaserJet and Inkjet.
• Plotters: plotters are used for high quality diagrams. A pen is mounted on an arm, which moves along the paper with the help of motors. This is used in making high-resolution sketches and maps.
• Speakers: helps in listening to music and soundtracks of applications.

Input/output devices
The information in the disks is read by a disk drive. It is this same drive, which helps in writing or recording information to the disks (hard disk, floppy disk, CD R/RW). Hence, the disk drive is called an input/output device.

HARDWARE AND SOFTWARE OF A COMPUTER

HARDWARE:
The components of the computer, which we can see, feel and touch, are known as the hardware.
Hardware comprises all the peripherals, which are associated with the computer.

SOFTWARE:
Software is a collection of Programs and instructions, which handle the different components of your computer and help them to interact in a hassle-free manner. Without software, a computer is nothing but a box with components that does not serve any purpose.
Computer software can be broadly classified into two categories viz:
(a) system software (operating system)
(b) application software(utility software)

SYSTEM SOFTWARE :
System software is the collection of programs and instructions designed to control, co-ordinate and extend the processing capabilities of a computer system. These programs act as an interface between the user and the computer.

APPLICATION SOFTWARE:
Application software are programs designed to use computer for a specific task. These programs are written to meet the needs of the user as the demand arises. Application software cannot function without system software. They give the user the flexibility to use the computer for special applications by providing with tools, which are otherwise not available with the system software. Examples of application software include Microsoft office, office XP, Adobe package, flash etc.

DISK OPERATING SYSTEMS:
Disk operating system is the operating system for personal computers (PCs).DOS provides a set of commands that enable to access or manipulate information on disks as well as simply interact with the PC. DOS manages file operations (copying, printing, viewing etc) disk storage organization, screen displays and other routine tasks that help make a PC easier to use. Software itself is contained on a disk and generally is loaded from that disk each time the computer starts up or boots.

Peripheral, Universal Serial Bus (USB) and Drivers

Peripheral

Hardware you add to your computer other than processors and memory is called a peripheral. Computers generally include a parallel port, one or two serial ports, two PS/2 ports, two universal serial bus(USB) ports, controllers for up to two floppy disk drives and four IDE devices(typically hard drives, CD-ROM drives, CD-R drives, or DVD drives), a modem and sound and video adapters on the motherboard. Windows can’t usually tell whether these items are built-in or on separate cards. It treats them all as separate peripherals.

Universal Serial Bus (USB)

USB is a new connector, intended to be a faster and simpler replacement for serial and parallel ports, as well as for low to moderate speed devices such as modems, printers, sound cards and back-up tapes.

Drivers

Windows comes with standard drivers for a wide range of monitors, printers, modems, and other devices. When you buy hardware, you usually receive a floppy disk or CD- ROM that contains the driver for the device which you need to install during the configuring process to get the device work with windows.

COMPUTER LANGUAGES

BINARY NUMBERS:

Computers can understand only binary numbers which are 0 and 1.


Any number or character can be operated by the computer in the binary format only.


The number 10 in binary number system is 1010.


The decimal number is representated in (base 10) and binary number is representated in (base 2).


eg. (10)10 = (1010)2


How to convert a decimal number to a binary number?

The following is a method to convert a decimal number to a binary one:


1) Divide the decimal number by 2.


2) Mark the reminder as the right most digit of the binary number.


3) Repeat the step 1 till the divident becomes 1. This 0 is the left most digit of the binary number.