Internet

Internet is a collection of local, regional and national computer networks that are linked together to exchange data and distribute processing tasks. The Internet evolved over the past thirty years from a fledging experiment with four computers into a vast information network that connects millions of microcomputers, minicomputers and mainframe computers. As of 1998, the Internet had more than 100 million users world wide, and that number is growing rapidly. The Internet is decentralized by design and, remarkably, this anarchy by design works well.

An ISP (Internet Service Provider) is a company that charges an ongoing fee for providing Internet access to businesses, organisations and individuals. The ISP provides the user with the necessary communications software (such as e-mail) and user account. The user supplies a modem that connects the computer to the user’s phone line. The user’s computer dials the ISP’s computer and establishes a connection over the phone line. Once connected the ISP routes data between the user’s computer and the Internet. Most ISPs offer dial-up Internet connections and electronic mail access, along with additional services. Some ISPs offer direct access to the Internet without the use of proprietary software.

World Wide Web is a computer network system that allows users to browse through information available
on computers round the world. The World Wide Web opened the Internet to millions of people interested in finding information. There are over one million Web sites around the world and the number is growing very quickly. The World Wide Web consists of documents called Web pages that contain information on a particular topic. A Web page might also contain one or more links that point to other Web pages. Links make it easy to follow a thread of related information, even if the pages are stored on computers located in different countries. Every Web page is stored as an HTML (HyperText Markup Language) document. An HTML document contains special instructions called HTML tags that tell a Web browser how to display the text, graphics, and background of a Web page. Uniform Resource Locator (URL) is the global address of documents and other resources on the World Wide Web. URLs can point to executable files that can be fetched using FTP (file transfer protocol, ftp://) or a Web page that can be retrieved using HTTP (hypertext transfer protocol, http://). To request a Web page the user either types in the URL address or uses a ‘mouse’ to click on a Web page link. After the http://, the next segment of the address is the server name. The server is the computer and software that make the data available. Most Web servers have domain names prefixed with WWW. By entering the Web server name, one accesses the site’s home page (The main page of a Website. Typically, the home page serves as an index or table of contents to other documents stored at the site). A home page is similar to the title page and table of contents in a book. It identifies the site and contains links to other pages at the site.
The Web browser is the gateway to commercial information services as well as the free sites on the Internet. A commercial information service provides access to computer-based information for a fee. In 1997, approximately 17 million people subscribed to the top four commercial information services: America On-Line, CompuServe, Microsoft Network and Prodigy.
The server sends the data for the Web page over the Internet to the computer. The data includes two things: the information the user wants to view and a set of instructions that tells the browser how to display it. The instructions include specifications for the colour of the background, the size of the text, and the placement of the graphics. Additional instructions tell the browser what to do when the user clicks on a link. The browser’s menu and tool bars help users navigate the Web as they follow the links. The Back and Forward buttons trace and retrace the users’ path through the links being followed from one Web page to another. The browser stores and can display a list of the pages being visited during each session. The browser can also store a list of favourite sites, often called bookmarks, to permit the user to jump directly to the site they wish to see instead of having to enter its URL every time.

Networking Computing

A network computing environment is one in which an organization has linked together personal computers that have been connected into a network. There are a number of types of computer networks.
Local area network: A computer network located within a relatively limited area such as a building, agency or university campus. Also known as a LAN.
Wide area network (WAN): A computer network that covers a large geographical area.
The purpose of networking personal computers and even mainframes together is to permit employees in the organization to
• communicate with one another as well as others outside the organization, normally through the use of electronic messages
• access information and services supported on the World Wide Web
• share documents and data
• support various work processes in the organization based on the automation of specific tasks.
A computer that is not connected to a network is referred to as a stand-alone computer. When a computer is physically connected to a local area network, using a cable or other communications channel, the computer becomes a workstation on the network. Each device on the network including workstations, servers, and printers is referred to as a node.
A workstation normally has all of the usual resources found in the personal computing environment (hard drive, software, data and printer). However, users of workstations will also have access to network resources, which typically include application software, storage space for data files, and printers other than those on the local workstation. On a network, the network server typically provides the applications
software and storage space for data files.
An application server is a computer that runs applications software and runs the results of processing to workstations as requested. An application server makes it possible to use the processing power of both the server and the workstation. Use of an application server splits processing between the workstation client and the network server. The method is also referred to as client/server architecture.
The main advantage of a computer network is that all the users can share resources, rather than have users each maintain his or her own resources. It is not necessary to purchase multiple copies of software; instead a license can be purchased to use the software within the network which allows everyone to use the program at the same time.
An internal network that belongs to an organization and is accessible only by that organization members is often referred to as an Intranet. Intranet is an internal computer network that belongs to an organization and is accessible only by that organization's members.

Mainframe computing

Mainframe computing was developed at a time when computational power was an expensive and scarce resource. In order to use the expensive computer technologies efficiently, organizations had to share their resources. Many of computerized such as invoicing, purchasing, payroll, accounting and so on, involved the organization as a whole.
If the original reasons for the mainframe computing model were cost and scarcity of resources, the current reasons for sharing computer power are

• for security: the protection of data from outside or unauthorized access
• for integrity: the guarantee that the data is not corrupted and that repeatability is achievable using the same applications and data
• for system availability: centralized facilities can be operated by teams in shifts 24 hours a day, maximizing the investment in IT equipment and allowing large data processing activities to be carried out efficiently
• for data sharing: data input or created in one part of the organization becomes available to other parts
• for applications: many modern applications, such as personnel management systems, require access to a shared pool of resources.

Nowadays, mainframe computing is no longer an expensive resource, sharing is still a cost-effective means of providing computational power. Recent studies have shown that on a per-user basis, mainframe computing provides the least expensive form of computing.
A large central processor is kept in a purpose-built computer centre staffed by personnel responsible for maintaining it. Individuals in the organisation access the mainframe computer through terminals on their desktops in order to share common organisational resources, such as software programs or electronic data. Nowadays, a mainframe is actually identified more by the ‘environment’ in which the mainframe is operated. In other words, the physical environment: the controlled temperature and humidity and the physical security of having the mainframe behind locked doors.

The mainframe is the data and application repository for most organizations. It is also the hub for most online business activities. It is believed that mainframes still house 90 per cent of the data major organizations rely on to conduct their business. Despite claims that mainframe technology is dying out, sales of mainframe hardware and software remain steady. The term ‘mainframe’ has always had the image of being something large in size. Yet, however big the early ‘room-filling’ mainframes were, today’s modern versions are no bigger than the size of a household refrigerator. The level of mainframe sophistication has grown over the more than thirty years of its evolution; organizations still recognize its advantages in terms of performance, reliability and security.

Virus

It is a computer program that is planted in one computer and then transferred, hidden in useful information, to one or more other computers with the intention of corrupting or wiping out information in the recipient computer. Many different types of viruses exist, ranging from ones that prevent us from opening up word-processed documents through to ones that destroy the entire contents of a hard drive. Viruses can be caught in several ways, for example by exchanging floppy disks, by electronic mail messages and through downloading documents from the Web. Networks make it much easier for viruses to move around. Once a virus gets into computer system it can spread very quickly. New viruses appear each week, so it is essential that users have up-to date anti-virus software to combat this problem.

Documentation

Documentation explains how the various systems or programs operate and accompany computer hardware, software and peripherals. It is the information needed to develop, use or maintain computer hardware and software and to permit access and retrieval of the data. Although documentation usually comes in the form of printed manuals, guide books, it may also come in electronic form, such as in ‘help screens’ contained within the computer software or documentation in data dictionaries and so on. Mostly, it is created when a specific computer application is used. This documentation can be critical to understanding the database system, particularly if it is being managed in an archival environment long after the creators of the system have left.

How are data stored?

A storage device is anything which is used to store computer data. Floppy disks, hard disks, optical disks,
CDs and magnetic tapes are types of storage device.
Physical storage refers to how data are actually kept on the storage disk. The most commonly used medium for storage is magnetic storage. With magnetic storage the computer stores data on disks and tape by magnetising selected particles of an oxide-based surface coating. The two most popular types of magnetic storage media are hard disks and diskettes.

Hard drive or hard disk storage provides faster access to files than a diskette. It is the storage area within the computer itself, where megabytes of space are available to store bits of information. A hard disk platter is a flat, rigid disk made of aluminium or glass and coated with a magnetic oxide. A hard disk consists of one or more platters and their read-write heads. A read-write head is the device that reads the data from the disk platter into the computer. It also writes data onto the platters. Hard disk platters in microcomputers are typically 3½ inches (about 10 centimetres) in diameter: the same size as the circular mylar disk in a diskette. However, the storage capacity of a hard disk far exceeds that of a floppy disk. The access time of a hard disk is also significantly faster than a diskette. Like diskettes, hard disks provide random access to files by positioning the read-write head over the sector that contains the requested data.

Diskette is a small, removable, flexible mylar plastic disk covered with a thin layer of a magnetizable substance, onto which digital data can be recorded and stored. Diskettes are also called floppies. Although today’s microcomputers typically use 3½ inch (about 10 centimetre) disks, we may still find 5¼ inch (about 15 centimetre) disks that were popular many years ago. Finding a disk drive to read 5¼ inch disks may be very difficult. Diskettes are generally used for transporting or shipping data files or for making duplicate copies of data files for back-up purposes. The storage capacity of a diskette varies but is considerably smaller than that of a hard drive.
Other types of storage devices are:
Magnetic tape: It is a continuous plastic strip covered with magnetic oxide, the tape is divided into parallel tracks onto which data may be recorded by selectively magnetising parts of the surface, or spots, in each of the tracks. The data can then be stored and reused.
Back up: It is used to copy a computer files to another medium, usually on a diskette or magnetic tape, so that the data are safe in case the original file is damaged or lost. Backups are usually copied to storage devices that can be removed from the computer and kept separately from the original.
Optical disk: A storage device that uses reflecting surfaces and laser technology to read and write data on a disk is optical disk which is also known as a laser disk. Some types of optical disks are CD-ROM, CD-RW.

How a computer processes information.

When data is input into a computer, the numbers or words we understand are translated into a binary numbers system. Binary is the language of computers. Everything we type, input, output, send, retrieve, draw and so on is converted to the computer’s native language: binary ( it uses only two symbols 0 and 1 to represent values).

In the binary system, each digit position represents a value of 2. Because computers use the binary system, powers of 2 play an important role. This is why everything in computers seems to come in 8s (2 to the 3rd power), 64s (2 to the 6th power), 128s (2 to the 7th power), and 256s (2 to the 8th power).

The work of manipulating, storing and processing the data takes place in the Central Processing Unit, the computer’s main memory. The CPU consists of an arithmetic and logic unit, or ALU, a control unit, and a set of registers.

1. The arithmetic and logic unit is the portion of the CPU where arithmetic and logical operations take place.
2. The control unit is the part of the CPU that supervises the general operations of the computer.
3. The registers are devices that hold data inside the computer’s memory long enough to execute a particular function, such as indexing, calculating, sorting or otherwise manipulating data. They are the CPU’s own internal memory.

The medium through which the data are transferred from one part of computer to another is called bus. The data are input into the computer and processed in the CPU. They travel along the bus to be stored in the computer’s memory. The amount of memory available is described in bytes of information, referring to the combination of bits representing characters. The higher the number of bytes the more memory the computer has. Today’s computers hold ‘megabytes’ or even ‘gigabytes’ of data. A megabyte is a unit of one million bytes; a gigabyte is one billion bytes, and a terabyte is one trillion bytes. If a computer has a memory of 64 megabytes, then it can hold 64 million bytes of information.