Types of Operating Systems

           Operating system can be broadly classified into two categories based on the type of interface provided to the user. Command Line Interface          In these types of operating systems the user can enter commands through the keyboard and each command will perform a specific action. But this type of interface is very difficult for a beginner to use, because the commands have to be remembered.           MS-DOS is such a Operating System. Dos stands for Disk Operating system. It was developed by Microsoft as an operating system in the 1980s. Windows 3x needed DOS to run, but the later versions...

Read more »

Operating System

         An Operating System or OS is a software program that enables the computer hardware to communicate and operate with the computer software. Without an Operating System, a computer would be useless. Features Expected of an Operating System To Startup and Shutdown the computer.  To act as an interface between the user and the hardware. To perform house keeping tasks such as file handling, disk/ memory management. To be able to allow the user to configure the system. This includes changing the types of printers, adding new hardware (such as sound cards), etc. ...

Read more »

The Internet

   The Internet is a network of autonomous computer networks that spans the globe. It provides an infrastructure for global electronic information exchange. Today the Internet is used by millions of people of facilitate various activities such as business, education and plain communication.    The Internet grew out of a United States Department of Defense project, the ARPANET (Advanced Research Project Agency Network) started in late 1960s. Its main objective was to provide network links between universities, research organizations and remote computer centers.             The following figure shows how the Internet is structured. At the bottom level are the...

Read more »

How to Protect a Computer from Computer Viruses

        There are many ways of preventing a computer from virus attack. Some of these precautions are listed below. Verbal Warning Avoiding the use of unchecked disks Avoiding the use of unauthorized or unchecked software Anti-virus Software         Anti-virus software contains anti-virus scanners, which look for viruses. On-access scanners - Automatically check the hard disk and diskette each time the system starts up. On-demand scanners - Executes only on users demand and can be scheduled to run at various times        Most commercial anti-virus software provides both types of scanners. It will take some time for an anti-virus software designer get to know about a new type of...

Read more »

Main Types of Virus

Boot Virus           Boot virus infects the boot sector of the hard disk and is activated every time the computer is switched on. Once infected, the computer may fail to start properly. Usually boot viruses spread from the boot sectors in floppy diskettes to the boot sector of the hard disk. When you start up the system with an infected diskette in the diskette drive, the virus transfers from the diskette to the boot sector of the hard disk. Once infected, the virus may remain in the main memory and infect other diskettes. File Virus (Parasitic Virus)          File viruses are virus programs attached to executable files. They become active every time the program is executed. Macro Virus         ...

Read more »

Main Phases of Virus Activity

The main phases of virus generally follows are; Gains access to the system Lies dormant Propagates Virus is triggered by some event Virus Action ...

Read more »

Popular Viruses and Worm Programmes

2000            May : The VBS/Loveletter ('ILOVEYOU') worm appeard. As of 2004 this is the most costly virus to business, causing upwards of 10 billion dollars in damage.   2001             January : A worm strikingly similar to the Morris worm, names the Ramen worm infected only Red Hat Linux machines running version 6.2 and 7.                July 13 : The Code Red worm attacking Microsoft Internet Information Services.                October 26 : The Klez worm is first identified.    2003              January 24 : The SQL slammer worm also known as the Sapphire...

Read more »

Components of a Virus

A virus comprises of four general components. The replicator (or Engine) : Replicates the virus. The safeguard : Prevents the detection and the removal of the virus. The trigger monitor : Monitors for a specific condition to deliver payload. These specific conditions may be the arrival of a particular date, time, keyboard stroke, etc. The payload : the action it does apart from propagation. This action may be an amusing or malicious action resulting in distraction from the current work or destruction of data....

Read more »

Computer Viruses

Some of the main reasons for writing viruses are; Hacking. To prevent copying software. Revenge - Employees may plant "Time Bombs" in programs. Fraud - Viruses may allow access to an otherwise secure system. Political and terrorist motives. Commercial sabotage - Damage the reputation of a competitor. Warfare - Incorporate a virus to an enemy's computer. Viruses can be transmitted from one system to another through various media types such as; Floppy disks. Tape backups. Internet. Software. Some of the symptoms that a computer will show up when infected with a virus are listed below. Programs take long time to lead than normal. The floppy disk drive or hard drive runs when you are not using it. New files keep appearing on the system and you do not know where they come from. Strange...

Read more »

Network Protocols

           A network protocol is "an agreement on how to converse". The four most commonly used network protocols are TCP/IP, IPX/SPX, X.25 and SNA. Each protocol performs essentially the same functions, but each protocol is incompatible with other unless there is a special device to translate between them. TCP/IP Network Addressing               TCP/IP protocol uses 3 different types of addressing to move data between computers: Physical, Logical and Port addresses. The physical addresses (MAC addresses) are utilized to move data within a single LAN, logical addresses (IP addresses) are used to move data from one LAN to another LAN across the network and the port address...

Read more »

Backbone Network Components

         A backbone network is a network that connects many networks in a single site. There are many backbone network components. Router - A router is a special device that enables the connection of two or more networks so that the computers in different networks can communicate with each other. A router may be a special device, a computer with several network interface cards or a special network module in a computer or other network device. Routers also allow a network to be segmented into smaller logical networks or subnets. Bridge - A Bridge is an interface that enables similar networks to communicate. Gateway - A Gateway is an interface that enables dissimilar networks to...

Read more »

Data Transmission Types

       In a network data can be transmitted in two different ways, serial transmission and in parallel transmission. Serial Data Transmission - Bits are transmitted sequentially, one after the other. Parallel Data Transmission - Bits are transmitted through separate channels simultaneously.      The standard unit of measure used to specify the speed of the data flow through a network is bits per second (bps). Network Interface Card (NIC)  A network Interface Card provides the physical connection between the computer and a network cable and enables access to a network. Most modern computers come with NIC cards pre-installed, and ready to be connected to networks.  Types...

Read more »

Communication Media

           The communication media is the matter or substance that carries the voice or data. Many different types of transmission media are currently in use. All these different media types can be grouped into two categories: Guided media and Radiated media. Guided Media           The guided media are those in which the data flows through physical media. Twisted-pair Wire - A twisted-pair wire consists of two insulated copper wires, twisted around each other and covered in another layer of plastic insulation. Coaxial Cable - A coaxial cable consists of insulated copper wire wrapped in a metal shield, which is then wrapped in an outer external...

Read more »

Network Topologies

           Networks can be laid out in a number of different ways. The physical layout of a network is called its topology. The basic network topologies are Star, Ring, Bus. These basic topologies can be combined in a variety of ways to build complex hybrid network topologies. Star Topology            In a star network all computers and other communications devices are connected to a central point such as a hub, file sever or a host computer. Ring Topology             In a ring network all communications devices are connected in a continuous ring. Messages are passed around the ring until...

Read more »

Data Communications

           Data Communication is the process of moving information from one point to another by means of some transmission system. Network           A network is a collection of entities that exchange information or good. Few examples of networks are railway system, nervous system of animals, telephone system. Communications Network           A communications network is a system of interconnected computers, and communication devices that can communicate with one another and share resources. At the most elementary level, a computer network consists  of two computers connected with...

Read more »

Application Software

               Application software is designed to perform useful general-purpose tasks. For example, an application program called Solitaire is a single program that lets you play a card game. Application software can be grouped as customized software or as application packages. Customized software is generally designed for a particular customer whereas application packages are "off the shelf" programmes designed for the general public. Common types of application software are: Word Processing Spreadsheet Database Management System Presentation Software Desktop Publishing and Graphic Design Web Design and Development Device Drivers               ...

Read more »

System Software

Software           Software refers to instructions which are used by  the computer to perform various tasks. The word programme is synonymous with software. Software is created with programming languages and related utilities. Software is generally classified into two types: System Software and Application Software. System Software           System software is responsible for controlling, integrating and managing the individual hardware components of a computer system so that other software and the users of the system see it as a functional unit without having to be concerned with the low-level details of the computer hardware. System software can be further classified as: Operating Systems. Utilities...

Read more »

Different Types of Printers

            Many different types of printers are in use today. Two primary technologies used for printing are impact printing and non-impact printing. Impact Printers use a print head containing a number of metal pins which strike an inked ribbon placed between the print head and the paper. The non-impact printers are much quieter than impact printers as their printing heads do not strike the paper. The Most Common Printer Types Are: Dot matrix printers, Ink-jet printers, Laser printers.  Dot Matrix Printers               These printers work by firing a matrix of tiny pins (which are located in the...

Read more »

Different Types of Display Screens

CRT Monitor                   A cathode-ray tube and associated electronics connected to the video output of a computer. These have higher resolution than TVs. Lager monitors with high resolution are used for specialized application such as desktop publishing and CAD. LCD (Liquid Crystal Display) Monitor                LCDs are screens made from two glass/plastic plates with liquid in between. LCDs are commonly used for calculators and laptop computers, as they are far flatter than is possible with cathode ray screens used in TVs and Standard computer monitors. Main difference...

Read more »

Different Types of Output Devices

             Output devices translate information processed by the computer into a form that either humans or other machines can understand. There are a variety of output devices, which can be connected to a computer. Some of the common output devices are explained in the following sections. Monitor             The most common form of output is the computer screen. It is more correctly called 'monitor' and sometimes referred to as the visual display or VDU.              The quality of a computer monitor is based on the following properties: Resolution: Resolution is the number of pixels, which the screen can display. A 'pixel' is the...

Read more »

Different Types of Input Devices

Formatting             Hard disks and Diskettes must be formatted before saving data on them. Formatting can be considered as an initialization process that prepares the disk or diskette electronically so that it can store data or programs. Input Devices             Input devices enable data to be fed into the computer in a form that the computer can use. Input devices are categorized into two types: keyboard entry devices and direct entry devices. A devices through which data can be entered to the computer by pressing keys is called a keyboard entry device whereas all the other types of input devices are called direct entry...

Read more »

Different Types of Memory

Floppy Disk            A floppy disk or a diskette is a round flat removable piece of plastic coated with a Ferric Oxide layer, and encased in a protective plastic cover, called the disk jacket. The Ferric Oxide layer is capable of holding a magnetic field. Data is stored on a floppy disk by means of a disk drive, which alters the magnetic orientation of the particles in the Ferric Oxide layer. Reading data from a diskette means that the data stored as a magnetic pattern on a diskette is converted to electronic signals and transmitted to the memory of the computer. Writing data on a diskette means electronic information is transformed into magnetic patterns and recorded magnetically on...

Read more »

Components of a Computer System

                  By considering the functions performed by various components, a computer can be represented as a collection of logical components as in Figure 1.3. The main hardware components of a modern computer system are the central processing unit (CPU), the main memory, the secondary storage and the In put-Out put devices.   System Unit                   The system unit, or the cabinet houses most of the essential components of the computer system such as the power supply, the motherboard, the CPU chip, specialized chips, the system clock, RAM,...

Read more »

Data Representation

             Computers use the two-state system to represent data. Such a two state system is referred to as a binary system. In computers these two states are denoted by the digits 0 and 1 and any such value is called a binary digit or bit. In side the computer these two states are typically implemented by using two different voltages.              The smallest unit of data that can be stored in a computer is a bit. A bit will have the value '0' or '1' . A large collection of such '0's or '1's is what makes up data in a computer. Smallest Unit           = 1 bit8 bits                 ...

Read more »