Clients and Servers

Client and server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfils the request. Although the client/server idea can be used by programs within a single computer, it is a more important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common. 

Internet servers make the Internet possible. All of the machines on the Internet are either servers or clients. The machines that provide services to other machines are servers. And the machines that are used to connect to those services are clients. There are Web servers, e-mail servers, FTP servers and so on serving the needs of Internet users all over the world. 

When you connect to www.yahoo.com to read a page, you are a user sitting at a client's machine. You are accessing the Yahoo Web server. The server machine finds the page you requested and sends it to you. Clients that come to a server machine do so with a specific intent, so clients direct their request to a specific software server running on the server machine. For example, if you are running a Web browser on your machine, it will want to take to the Web server on the server machine, not the e-mail server.

A server has a static IP address that does not change very often. A home machine that is dialling up through a modem, on the other hand, typically has an IP address assigned by the ISP every time you dial in. That IP address is unique for your session, it may be different the next time you dial in. This way, an ISP only needs one IP address for each modem it supports, rather than one for each customer.

Uniform Resource Locators (URL)

When you use the Web or send an email message, you use a domain name to do it. For example, the Uniform Resource Locator  (URL) "http://www.yahoo.com" contains the domain name yahoo.com.com. So does this email address: abcdf@yahoo.com.com. Every time you use a domain name, you use the Internet's DNS servers to translate the human-readable domain name into the machine-readable IP address.

Top-level domain names, also called first-level domain names,include.COM, .ORG, .NET, .EDU and .GOV. Within every top-level domain there is a huge list of second-level domains. For example, in the .COM first-level domain there is:

* Yahoo

* Microsoft

Every name in the .COM top-level domain must be unique. The left-most word, like www, is the host name. It specifies the name of a specify machine (with a specific IP address) in a domain. A given domain can, potentially, contain millions of host names as long as they are all unique within that domain.

DNS servers accept requests from programs and other name servers to convert domain names into IP addresses. When a request comes in, the DNS server can do one of four things with it.

i. It can answer the request with an IP address because it already knows the IP address for the requested domain.

ii. It can contact another DNS server and try to find the IP address for the name requested. It may have to do this multiple times.

iii. It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a DNS server that knows more than I do."

iv. It can return an error message because the requested domain name is invalid or does not exist.

IP Address

Internet Protocol : IP Addresses

Every machine on the Internet has a unique identifying number, called an IP Address. The IP stands for Internet Protocol, which is the language that computers use to communicate over the Internet Protocol, which is the language that computers use to communicate over the Internet. A protocol is the predefined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a Web browser.

A typical IP address looks like this :

192.168.10.1

To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a dotted decimal number like the one above. But computers communicate in binary form. Look at the same IP address in binary:

11000000.10101000.00001010.00000001

The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32 bit numbers. Since each of the eight positions can have two different states (1 or zero), the total number of possible combinations per octet is 2^8 or 256. So each octet can contain any value between zero and 255. Combine the four octets and you get 2^32 or a possible 4,294,967,296 unique values.

Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts.

The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host action always contain the last octet.

Early Networks

Definition :

A computer network, or simply a network, is a collection of computers and other hardware interconnected by communication channels that allow sharing of resources and information.[1] Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. Simply, more than one computer interconnected through a communication medium for information interchange is called a computer network.

* In 1973, engineers began to look at ways to connect ARPANET to the packet radio network (PRNET). A packnet radio network connects computers through radio transmitters and receivers. Instead of sending data across phone lines, the computers use radio waves. It took three years, but in 1967 engineers successfully connected the two networks.

* Technicians joined the Satellite Network (SATNET) to the other two networks in 1977. They called the connection between multiple networks inter-networking, or the Internet for short. Other early computer networks soon joined. They included USENET, BITNET, CSNET and NSFNET.

* In 1990, Tim Berners-Lee developed a system designed to simplify navigation on the Internet. In time, this system became known as the World Wide Web. It didn't take long for some people to mistakenly identify the Internet and the Web as the same thing. The Internet is a global interconnection of computer networks; the World Wide Web is a way to navigate this massive network. In sailing terms, It's like comparing on ocean to a ship.

* Most early Internet users were government and military employees, graduate students and computer scientists. Using the World Wide Web, the Internet became much more accessible. College and universities began to connect to the Internet, and business soon followed. By 1994, Internet commerce had become a reality.

* Today, the Internet is more complex than ever. It connects computers, satellites, mobile devices and other gadgets together in a massive network millions of times more intricate than the original ARPANET. And to thing, we owe it all to a silver beeping ball that once orbited miles above the Earth's surface.

How did the Internet Start

Introduction :

Just imagine all the cities in the world having wonderful streets but no connections between them not even footpaths, it would be very critical existence for everyone. That was the way the computer would was until a few years ago. Now the computer world is rapidly increasing, over the past decades many computers have been linked together in seconds and companies, so users can exchange data over the networks. Over the past few years, the local grouping of computers called Local Area Networks have been connected together into a world wide network by the Internet. This vast electronic web has been named cyber space, which is a world where everyone connected electronically.

How did the Internet Start ?

In the 1950s, computers were enormous devices that filled entire rooms. They had a fraction of the power and processing ability, we can find in a modern PC. Many computers could only read magnetic tape or punch cards, and there was no way to network computers together.

ARPA aimed to change that. It enlisted the help of the company Bolt, Beranek and Newman (BBN) to create a computer network. The network had to connect four computers running on four different operating systems. They called the network ARPANET. It's original purpose was to link several computer sites in the country so that if one was destroyed the others would still function. It became so successful that universities, government departments and large corporations began to link to it also.

Without ARPANET, the Internet would not look or behave the way it does today, it might not even exist. Although other groups were working on ways to network computers, ARPANET established the protocols used on the Internet today. Morever, without ARPANET, it may have taken many more years before anyone tried to find ways to join regional networks together into a larger system.

System Software

A set of program that govern the operation of a computer system and make the hardware to work. It controls internal computer operations of the computer system. System software refers to the files and programs that make up your computer's operating system. System files include libraries of functions, system services, drivers for printers and other hardware, system preferences, and other configuration files. The programs that are part of the system software include assemblers, compilers, file management tools, system utilities, and debuggers. The system software can be divided into two types,

i. Operating System

II. Language Processors

1. Operating System :

An operating system plays an important role in a computer system which controls all other components of the computer system. If there is no operating system, then  there is no computer. It controls the CPU, Memory, Input/Output devices etc. It is responsible for smooth functioning and efficient operation  of the computer system. Some of the popular operating system are DOS,WINDOWS, UNIX and LINUX etc.

2. Language Processor : 

A programmer can write program in high level language because it is much easy to understand by the computer and convert into its own machine language. The system programs which perform on language processors i.e., it converts the high level language program into machine understandable form (Machine language). The language processors are Assembler, Interpreter,Compiler.

Software Development Life Cycle

1. Requirement Analysis :

The objective of the requirement analysis is to identify and document the user requirements for the proposed system. It is also the process of understanding what is needed or wanted, and expressing the result in writing. This is the process of understanding and putting in writing, a statement of what the application is intended to do, once it has been built. This is the first and perhaps the most important step in the software development. The main objective of the requirements analysis is to produce a document that properly specifies all requirements of the customer. That is called the Software Requirement Specifications (SRS) document is the primary output of this phase. This process involves Analysis who meet with interview and observe knowledgeable users to understand what the requirements are, In addition existing system, processes, documents and producers are also reviewed.

2.Design Process:

The design phase is the process of designing exactly how the specifications are to be implemented. It defines specifically how the software is to be written including an object model with properties and methods for each object, Analysis and design are very crucial in the whole development cycle. Any glitch in the design phase could be very expansive to solve in the later stag e of the software development, so much care is taken during this phase.

3. Development or Coding :

The design must be translated into a machine-readable form. The coding or development step performs this task. the development phase involves the actual coding of the entire application. If design is performed in a detailed manner, code generation can be accomplished without much complication programming tools like Compilers, Interpreters, Debuggers are used to generate the code. Different high level languages like C, C++, JAVA, COBOL etc., are used for coding, with respect to the type of application, the right programming language is chosen.

4. Testing :

Testing is the process of executing the proposed software with sample or test data and put it into regular use. Once the code is generated, the program testing begins. There are different testing methodologies are available to unravel the bugs that were committed during the previous phases. Different testing tools and methodologies are already available some companies built their own testing tools that are tailor made for their own development operations.

5. Implementation and maintenance :

The implementation phase is a staged roll out of the new application. This involves installation and initial training and may involve hardware and network upgrades. Software will definitely undergo changes once it is delivered to the customer. Thus are many reasons for the change. Changes could happen because of some unexpected input values into the system. In addition, the changes in the system could directly affect the software operations. The software should developed to accommodate changes that could happen during the post implementation period. The maintenance phase of the project is the last component and it continues as long as a warranty, extended warranty or support contract is in  place.

System Development Life Cycle

These are the sequence of events considered by the system analyst, or designer to built the new system or to replace the old system. The development of an information system throughout the system development life cycle involves continual and clean communication among the user and system personal and the people responsible for designing and implementing the system.

1. User :

The user is the person or persons, who will use the system or software once it has been installed.

Eg: Users include the operators, who run the computers and managers who require information from the system.

2. System Personal :

The system personal include system Analysts, System Designers and Programmers.

3. System Analyst :

A system analyst is the person, who works with users to determine their information needs or a System Analyst is the person who is having central control over the system.

4. System Designer :

A system designer is the specialist, who designs a system or software to fulfil the users information needs.

5. Programmer :

A programmer is the person, who codes the instructions that solve a problem in a programming language, so that, they can be used by the computer. In developing the system or software, to make the communication process easier and more efficient. A Project Management Team is oftenly established.

6. Project Management Team :

The Project Management Team usually consists of a Project Manager and depending on the size of the project, various number of users, system personnel, programms and other specialists.

Application Software

1. Word Processing (MS-Word) :

MS-Word is a Word processing program which involves the transformation of written text into a form, that gives it a format, systematic look that facilities easy reading.

A Word is a Computer based program, that 

* Is used to type text.

* Correct Spelling and Grammar errors as we type.

* Let us Preview the complete text before it can be printed and we can organize the data into lists and then summarize,    compare and present the data graphically.

* Let us change a variety of characters and fonts.

* Allows us to add Headers and Footers.

* Allows us to produce personalized letters through Mail Merge.

* Allows us to share resources available to all office programs, such as Clip Arts, Drawing tolls etc.,

2. Spread Sheet Package (MS-Excel) :

Excel is a spreadsheet program, and is used to present financial data such as budget or sales report etc.

Excel allows : 

* To enter and edit data in a Worksheet.

* To use functions and Formulae to calculate and analyze data.

* To create colourful Charts and Graphs.

* To save time by combining a series of commands into a single command by using MACROS.

* To manage and analyze a large amount of data in to a list.

3. Presentation Package (MS-PowerPoint) :

PowerPoint is a program that helps us to plan, organize and design professional presentations. We can use our computer screen for 35mm slides or overhead projectors to deliver a presentation. We can also print handouts to help the audience to follow the presentation.

PowerPoit allows :

* To edit and organize text in a Presentation.

* To add objects to the slides in a presentation (such as, Shapes, Pictures, Clip Arts, and Charts).

* To change the colour schemes in presentation.

* To Animate the presentation.

* To add slide Transition.

4. Database Management System (MS-Access) :

Access is a full featured Relational Database Management System (RDBMS) that allows us to store and manage large volume of information.

By using Access :

* We can store large volumes of information in the form of tables.

* We can print reports as per our requirements.

* We can create Forms (Forms helps us to quickly view, enter and change information in a database).

* We can create queries (Queries help us to find specific information in a database).

Access uses a number of shared office resources as do the other applications. These includes Fonts, ClipArt, Spelling resources, AutoCorrect, etc.

5. Communication Package (MS-Outlook) :

Outlook is a full featured desktop communication information program,that helps to manage information and time more efficiently and enables us to share information.

The features in Outlook are 

* Create a new mail message

* Read mail

* Create a new news message

* Read news

* Subscribe to news groups

* Open the address book

* Find people etc., 

Functions and Types of Operating System

1. Functions of Operating System :

* It loads itself into the computer memory.

* It loads user programs and data into the computer memory.

* It allocates various jobs to various resources.

* It controls and co-ordinates the entire computer system.

* It provides 'Housekeeping' and 'File management' utilities that perform useful tasks such as,

   ~ Disk preparation (formatting, partitioning etc.,)

   ~ File operations (creating, displaying, copying, combining, renaming and deletion of files etc.)

* It Automates the repetitive tasks through automatic execution, through the batch, files.

* Controls the way of displaying information on the screen.

* It controls the various application programs, such as word processors, electronic spreadsheets, database management programs, accounting programs, etc.

* Scheduling new jobs for execution according to the desired priority.

* Maintaining security, communication of errors and control measures to the users.

2. Types of Operating System :

The various types of operating systems are 

* Single user operating system 

* Multi-user operating system 

* Time sharing operating system 

* Virtual storage operating system 

* Real time operating system 

* Multiprocessing operating system 

* Operating systems as virtual machines/Virtual machine operating system.

Relationship between Software and Hardware

To get any useful output from the computer, the software and the hardware must work  together. We can't do any task on the computer hardware, without the software, So we must incorporate the appropriate software on the computer hardware.

i. It is the process of loading the particular software into the computer to use its function. 

ii. It is the process of mounting the different computer peripherals or components into one to make the computer system function properly.

1. Software :

* It is the collection of programs to perform a particular task.

* There are so many different types of softwares available for different purposes.

* The softwares are categorized as system softwares and application softwares.

* Without the software, we can not do any task using the computer.

* Adequate training is necessary to use the software.

* Software is continuing expenses.

2. Hardware :

* It is formed as the physical components of the computer system.

* All of the hardware parts may do different tasks such as Hard disk is for storing, Keyboard is for giving inputs etc., 

* The hardware peripherals are also categorized such as 1 GHz Microprocessors, 2 GHz Microprocessors and so on.

* Without the hardware, there is no computer.

* Adequate training is necessary to use the hardware.

* Except for upgrading, it is one-time expense.

Limitations of Computer

A computer is a machine that can perform only within the limits set by the program. There can be two types of limits to computer operations, namely

i. Internal 

ii. External

1. Internal :

Computer has no intuition and ability to adapt. It cannot learn from past experience nor can it think, reason or discover. It cannot take decisions on its own. If incorrect information is fed into the computer, it will give incorrect result. A computer has no capability to anticipate nor can it act beyond instructions given to it. If there is a slight variation in the instruction given contrary to the intented one, it can not correct and it would only obey the incorrect instructions. In this case a human being can detect the error and suggest corrective action.

2. External :

In addition to a faulty program or wrong input data there could be errors due to power failures and voltage problem. The computer systems are also open to corruption due to viruses. Virus is a software program that affects the integrity of the operating system and/or data files. A virus may be introduced intentionally or by use of infected discs. Viruses are usually capable of reproducing themselves and can spread rapidly throughout the computer system. Another limitation with a computer system could be the absence of suitable security measures. Installing a computer system is quite expensive and moreover time consuming. Since the hardware technology is rapidly advancing, a computer may be technologically obsolete before it is installed.

Cables and Connectors

Before using a computer, we should be able to identify different cables and connectors that are connected to the computer.

1. Power cord :

The computer has two power cords. One connects the system unit to electric supply, and the other connects the monitor to the power supply or to SMPS of a system unit.

2. Monitor Cable :

One end of this is attached to the monitor. The other end, is a D-shaped connector with tiny pins, plugs into the port marked as 'video' or 'monitor' on the back of the system unit.

3. Mouse Cable :

The mouse connector is normally a 9-pin D-Connector or a round shaped connector called PS/2 which plugs into the Serial or COM1 port at the back of the system unit.

4. Keyboard Cable :

The Keyboard cable plugs into the round socket or a 9 pin D-Type connector labelled 'keyboard' at the back of the system unit.

5. Printer Cable :

Printers are supplied with a parallel cable or USB (Universal Serial Bus) Cable for connection to a computer. One end plugs into a port on the back panel of the computer system unit, and the other end plugs into the printer. Plug the large connector (Parallel) or small connector (USB) at the end of the printer cable, i.e., into the port at the back of the printer. Plug the other end of the cable into the parallel port or USB port on the back of the system unit. This may be Labelled  "Parallel" or "LPTI" or "USB".

Scanner, Printer and Modem

Scanner:

A Scanner is a device that can transfer an image of a photograph or written information to the computer. Scanners can transfer typed text, graphs, diagrams and photographs to the computer. It acts like a photography machine. The difference is that, instead of just making another copy of it on paper, it stores it in the computer's memory .

Printer :

A Printer is a device that produces written images (numbers, alphabets, graphs, etc) on paper. After a document has been created on a computer, we can send it to a printer for a 'Hard Copy', generally known as a printout. The speed of the printer is rated either by 'pages per minute' (ppm) or by 'characters per second' (cps). Printers come in many different shapes, sizes and printing technologies.

MODEM (MOdulator and DEModulator) :

Modems are used for sending or receiving data through internet. They allow programs and data to be transmitted locally or around the world, and offer you a diverse range of features such as electronic mail, banking and travel reservations etc. A Modem enables our computer to transfer information through 'Cables' with another computer, if each has a compatible Modem. Some Modems include software that allows documents (files) created on our computer to be sent to remote FAX machines. The speed of the modem is measured in Kilobytes per second (KBPS). If the speed is higher, the transmission will be faster.

Mouse

 A mouse is a hand-held pointing device that allows us to control our computer without having to type instructions from the keyboard. A mouse is normally a rectangular shaped device, with a rubber ball embedded in its lower side and buttons on top.

* On the screen the mouse is indicated as an arrow. Moving the mouse in any direction on the mouse pad, moves the arrow in that direction on the screen.

* Sometimes the mouse pointer is indicated on the screen in the form of an I shaped mouse pointer. When you click the left mouse button at any point on the screen , a blinking cursor gets displayed on the screen.

* Pressing the left mouse button once and releasing it, is called 'Click'. It is used to activate certain function on the screen, such as pulling down menus, highlighting commands etc.,

* Doing two quick click is termed as a 'Double-click' and this operation is used to open windows, execute programs and menus.

* The hourglass symbol on the screen indicates that the system is processing data. we must wait until it becomes an arrow again. 

Cache Memory and Virtual Memory

1. Cache Memory :

A small memory between CPU and main memory is called cache memory. The access time closer to the processing speed of the CPU. Cache memory acts as a high-speed buffer between CPU and main memory and is used to temporarily store very active data and instructions during processing. Since the cache memory is faster than main memory, the processing speed is increased by making data and instruction needed in present processing available in the cache memory.

Advantages :

1. It stores the current information.

2. Reduces the access time.

3. Increases the performance.

4. Increases the speed of CPU.

5. Fast accessing.

2. Virtual Memory :

A process cannot be loaded in a system whose main memory size is less than the total memory required by the process.

A process cannot be loaded and has to keep waiting for its execution to start until sufficient free memory for loading the entire process becomes available. This may delay a process's turn around time to great extent. Virtual memory is a memory management scheme that overcomes this limitations by allowing the execution of processes that might not be completely loaded in the main memory. That is, it does not require the entire process not be in memory before the process can execute.

Magnetic Tape

Magnetic Tape is the oldest form of secondary storage device. It is one of the popular storage medium for storing large amount of sequential data. It is also used as a backup storage for data stored on on-line storage device.

The magnetic tape medium is a plastic ribbon usually 1/2 inch or 1/4 inch wide and 50 to 2400 feet long. It is coated with a magnetizable recording material such as iron-oxide or chromium dioxide. Data are recorded on the tape in the form of tiny invisible magnetized and non-magnetized spots on the coated surface of the tape.

Advantages :

1. Non-volatile memory.

2. Volumenous data can be stored.

Disadvantages :

1. Only sequential data processing.

2. Complex mechanism required.

3. After few days the data can be mounted to tape, we need to recall the data to store it into hard disk as and when required.

CD-ROM

CD-ROM (Compact  Disk - Read Only Memory) :

CD-ROM is also one of the commonly used secondary storage devices. The main advantages of CD-ROM is, they can store large volumes of data i.e., 700 MB to 1.4 GB and also they are cheaper and easy to handle. It is made up of small plastic disk, coated with aluminium or silver for magnetization. A layer of transparent plastic is further deposited on the disk. The data is recorded in spiral tracks and the data once recorded cannot be deleted or rewritten, but can be read any number of times.

In this technology, a high power laser is beam is used to record data by burning tiny pits in the surface of the hard plastic disk. To read the data, a low power laser beam is used to scan the disk surface. The data are stored in binary digits. When the laser beam reflects from the smooth surface of the disk it is interpreted as a 1 bit and when the beam enters the tiny pits it is interpreted as a 0 bit.

Advantages :

1. High storage capacity.

2. Easy to use in multimedia application.

3. Handled easily.

4. Can Read/Rewrite using CD-RW's.

5. Widely used.

Disadvantages :

1. CD Writing can be done carefully.

2. Should be kept free from dust and heat.

Floppy Disk and Hard Disk

1. Floppy Disk :

Floppy is a piece of a plastic that we put into a computer to store information. It is a small plastic magnetic disk enclosed in a stiff envelop with a radial slit, used to store data or program for a micro computer. Floppy disks basically come in two size - Floppy disks 5 1/4" and 3 1/2".

Floppy disk basically have three common features :

Label area, Read/Write opening, and Write protect notch.

Label area :

This area has been assigned to the label that can be fixed on the floppy which indicates what information/data is stored in it.

Read/Write Opening :

This is the area where the read/write heads of the floppy disk drive can access the disk. It means that through this area, the computer is able to read/write content from/to the floppy disk. It is advisable never to touch this area as this may lead to destruction of data stored in the floppy.

Write Protect Notch :

This prevents you or anyone else from accidently or deliberately changing or erasing anything from the diskette. It means when your diskette is write protected, we cannot add or delete any information to it. But we can read or copy the contents of that diskette on to the computer.

Inserting a Floppy Disk :

To insert a floppy disk, hold it with the label side up and towards you. Place the disk into the drive. When the drive reads or writes data, a red or green light glows. As long as the light is ON, the floppy should not be removed from it.

2. Hard Disk :

A hard disk, is also a permanent storage, where we can store lot of information. Capacity of a hard disk is measured in Megabytes (MB) or Gigabytes (GB) and they come in various different sizes. Usually every computer now a days comes with hard disk. The hard disk in the computer, can be partitioned into different sizes and labelled as C, D, E etc., The information in hard disk stored in circular magnetic disks called platters, in the form of program files and data files.

Components of CPU

CPU (Central Processing Unit) :

The CPU controls and executes all our computer operations. For example, it ensures that the correct character is displayed on the monitor when you press a key on the keyboard. Cables are connected into the back of the CPU with Keyboard, Monitor, Mouse, Printer etc.,  Usually the hard disk and floppy disk drive are inside the CPU.

Components of CPU :

The brain behind all processes of the computer is contained within the System Unit. Inside the system unit there are so many components available.

Important components are described below :

1. Motherboard : All the electronic components in a PC are mounted on a Printed Circuit Board (PCB), called the motherboard. Thin lines of metal on the surface of the fibreglass connect pins from one component to another, forming the computer's electronic circuits.

2. Processor :The Microprocessor, or Central Processing Unit (CPU), is the computer's most important component. It carries out all the operations inside the computer, Pentium II, Pentium III, Pentium IV, are some of the Latest CPUs.

3. RAM chips : When a computer is switched on and is running a program, RAM (Random Access Memory) is used for the purpose of holding the program and its data. But when the computer is switched  off, anything held in RAM is lost.

4. Empty RAM chip Slots : These slots let us expand our computer's memory by adding extra RAM chips or modules.

5. Floppy Disk Drive : Each floppy disk drive consists of a slot to accept a floppy disk, a motor that spins the disk and a recording/reading device that moves across the disk in order to write or read data.

6. Hard Disk Drive : It is our computer's main permanent storage unit, holding large amounts of data and programs. Unlike data held in RAM the information on the hard disk is not affected even when the computer is switched off. It remains permanent unless we instruct the computer to remove it or the hard disk is damaged.

7. Power Supply Box (SMPS-Switched Mode Power Supply) : All the components in a PC need electronic power supply. The SMPS converts the normal household electric AC supply to 5V and 12V DC supply. Usually 12V DC supply is connected to Motherboard, whereas 5V DC supply to other peripherals such as Floppy, Hard disk etc.

8. Expansion Slots : These long narrow connectors allow us to plug in expansion chords (also called adaptor chords), which offer extra options not available in a normal computer.

Eg : TV tuner can be attached to view TV in a computer.

9. ROM Chips : Read Only Memory (ROM) chips have data written on them during manufacturing, that tells the CPU what to do when you switch on your PC. The data always intact even if you switch off your PC. We cannot delete or alter the contents of ROM.

10. Speaker : The speaker emits the computer's sound output.

RAM and ROM

1. RAM (Random Access Memory) :

This is a part of computer's local memory, where the computer stores all the data and instructions it receives from input and the results as it works through its calculations.

RAM is short-term memory or volatile memory, i.e., when the computer is switched off, all the information disappears, whereas ROM is permanent memory. The random access memory requires very little time for access to each data and is considered to be the fastest memory. Generally, magnetic core memories and semiconductor memory systems fall in this category.

Each bit in a RAM stores information by means of electric charge, where the presence of an electric charge indicates a '1' and the absence a '0'. One variety of RAM is the so-called Dynamic RAM, where this electric charge tends to leak out in a few milliseconds, so that the information present in the RAM is lost (like a leaky tin which can hold water only for a short while).

Consequently, the sets of information stored in such RAMs need be refreshed periodically, before all the charge has leaked out. For this purpose, special refresh circuitry has to be provided. As against this, we have Static RAMs, which are not leaky and therefore do not require any refreshing.

They also tend to be faster, a typical Static RAM today has an access time of 80 nsec which means that it could take 80 nsec to read or write into any location. The Dynamic RAM is 120 to 120 nsec. However Static RAMs tend to be more expensive than their Dynamic counterparts and are not used for large memories.

2. ROM (Read Only Memory) :

It is permanently in-built in the computer at the time of its production. ROM is otherwise called firmware also. It stores a set of instructions permanently which instructs the computer how to work. In ROM, permanent data and programs like trigonometric and logarithmic functions are also stored. In one variation of this type of memory , known as Programmable Read Only Memory (PROM), the flexibility of data alteration is also provided.

Computer Uses

1. Computers in Entertainment :

The Computers are used in entertainment to create or enhance a production or performance. The tools have become more sophisticated that it is becoming almost impossible to distinguish between the real and the artificial in film and photography.

The Computers are widely used to create special effects in big budget movies. they are also extensively used behind the scenes to edit film during the production process. More music softwares allow us to edit recorded music or even create our own.

2. Computers in the Arts :

The computers are extensively used in the areas of Dance, Photography and many other Arts. The fluid movements of dance can be brought to life through animation.

The computer and the web allow us to visit most of the art museums in the world from the computer.

3D stereograms allow us to see a 3D object hidden inside a single image and this can be made possible with the computers.

Photos can be digitized by dropping them off at our local photostore or we can digitize our photos using the computer.

3. Computers in Science and Engineering :

The computers with higher performance are used to simulate dynamic processes in the area of Science and Engineering. The super computer have numerous application in the area of Chemistry and Physics.

In Medical Technology, Physicians are using information technology to understand the human body and to diagnose the disorders.

The Satellites are commonly used in Information Technology. They may simply relay signals from one point to another, eliminating the need for wires between locations using the computers.

In Topography technology, the topographic images can be created with few raw data using the computers. In an attempt to have a better understanding of Earthquakes, Scientists use the computer together and plot the data.

4. Computers in Education :

The computers have been used in schools since decades with the enhancement of technology, education softwares have become a major influence at all levels from elementary Schools to Universities.

The ability to connect computers and students together over a network, opens up fantastic educational opportunities through the Internet.

At colleges, computers are being used to teach courses like, the ones you are taking.

5. Computers in Mathematics :

The visual renderings of mathematical formulas are made easy and possible with the mathematical program using the computer. Formulas can also be created using simple mathematical function through the computers.

The problem of numerical analysis such as matrices can be carried out using the computers and they are also very useful in the area of Statistical calculations such as vital Statistical correlations, Regression, Analysis of variance and so on.

6.Computers in Training :

The computer training programmes in various organization are huge and expensive. To save money and improve performance, many organizations are using computer based training to train the people on the techniques they need to know in their jobs.

Internet VS World Wide Web

Internet :

The Internet is a worldwide, publicly accessible network of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online, chat, file transfer, and the interlinked Web pages and other documents of the World Wide Web.

Internet VS World Wide Web :

The Internet and the World Wide Web are not synonymous. The Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections, etc.

The Web is a collection of interconnected documents and other resources, linked by hyperlinks and URLs. The World Wide Web is merely a service accessible via the internet, along with many other services including e-mail, file sharing, and others described below.

The best way to define and distinguish between these terms is with reference to the Internet Protocol suite.

It is a collection of standards and protocols that is organized into layers. Each layer provides the foundation and the services required by the layer above. In this scheme, the Internet consists of the computers and networks that can handle Internet Protocol data packets.

Once the IP infrastructure is established, then other protocols are layered "on top." All these higher protocols know about the underlying network is that they are exchanging information with a computer at another IP address.

IP does not guarantee quality of service, so it is often combined with Transmission  Control Protocol to solve problems like data packets arriving of order or not at all.

The Hypertext Transfer Protocol (HTTP) is the application layer protocol that links and provides access to the files, documents and other resources of the World Wide Web.

Basic Operations and Capabilities of Computers

Basic Operations of a Computer :

The computer have the following five basic operations to carry out any task.

1. Input : It is the process of capturing or acquiring the information or it is the raw data or information. By using this we can do any process.

2. Process : It is the transformation process to convert the input in to output.

3. Output : It is the result, which comes from the transformation process or it is the outcome of the process.

4. Storing : It is the process of saving the data or information or instructions, so that they can retained and retrieved whenever required.

5. Controlling : It is the process of directing the manner and sequence in  which all the operations are to be performed.

Capabilities of Computers :

The following are the capabilities of computers :

1. Computers offer unmatched speed, performing computation faster than humans. The computers provide large capacities to store information and the capability to rapidly access this information. 

2. Computers undertake laborious and repetitive tasks relieving us for a critical, Creative activities.

3. Computers perform tasks repeatedly without errors, avoiding the fatigue that effects humans.

4. Computers can do critical and dangerous tasks that may be hazardous to humans.

5. Computers provide necessary information that we can use it in decision making.

6. Computers offer services in a wide range of development areas that previously did not exist.

7. Computers allow society to undertake new activities in various fields and to function more efficiently.

8. Computers provide new time dimensions for the working day and for the human concept.

9. Computers provide efficient and effective controls over humans.

10. Computers can hold a program of model which can be explored in many different areas. 

History and Versions of HTML

Tim Berners-Lee is the person who defined HTML. In 1990, Tim Berners-Lee was working at CERN (European Organization for Nuclear Research). He included the elements that could define title, paragraphs, hyperlink, headings, simple lists, address blocks and so on. But in that version of HTML there was no facility for producing tables or fill-in forms and images within a document.

In 1994, Tim Berners-Lee launched the World Wide Web Consortium (W3C) for producing standards for web technologies. W3C also defined the standards for HTML. As an outcome of W3C's efforts HTML 2.0 adopted web standard within it. The W3C released its HTML 4 recommendation in December 1997. The current version HTML4.01

which is now followed for producing web documents.

The meta language used to define the syntax for HTML 4.01 is SGML (Standard Generalized Markup Language).

In 1998, the W3C introduced the EXtensible Markup Language (XML) which is a restricted version of SGML. Then a new version of HTML came up, which is called XHTML (eXtensible HyperText Markup Language). The syntaxes of XHTML are defined using XML, rather than SGML.

Basic Internet Protocols

1. File Transfer Protocol (FTP) :

The file transfer protocol sets the rules for transferring files between computers. When user wants to download a file from the server FTP is used. There are various issues that must be solved during such file transfer. These issues can be described as follows.

1. client must have an authority to download particular file.

2. the hardware and software on both the computers might be different.

3. the data interpretation and data formats on client and server might be different.

FTP provides the mechanism to handle these issues internally and remains free from all these complications. FTP uses two connections between client and server. One connection is used for actual data transfer and other is used for control information (used for commands). This seperation of data and commands makes the FTP more efficient.

2. Hyper Text Transfer Protocol (HTTP) :

The Hyper Text Transfer Protocol (HTTP) is a request/response protocol. It is a communication protocol used to transfer the information on local area network and World Wide Web (WWW).

It's the network protocol used to deliver virtually all files and other data (collectively called resources) on the World Wide Web, whether they're HTML files, image files, query results, or anything else. Usually, HTTP takes place through TCP/IP sockets.

A browser is an HTTP client because it sends requests to an HTTP server (Web server), which then sends responses back to the client. The standard (and default) port for HTTP servers to listen on is 80. The GET and POST are two popular methods used by HTTP protocol. It is also called as a stateless protocol because this protocol is not able to maintain the previous conversation/information.

3. Simple Network Management Protocol (SNMP) :

SNMP is a protocol which enables network administrators to manage network devices and to diagnose network problems. The network management system is based on two main elements : a supervisor and agents. The supervisor is the terminal at which the network administrator requests for network management. The agents are found at the level of each interface connecting the managed devices to the network. With the help of these agents information on the different objects (such as switch, hub, router) can be collected. SNMP makes use of UDP connection4. for transferring the SNMP messages. 

4. Post Office Protocol version 3 (POP3) :

POP3 is used by local email clients (such as Microsoft Outlook Express). POP3 makes use of port 110. The POP3 protocol works only at the receivers end and has no works at the sender's end.

The POP protocol has two parts, a client POP i.e. receiver's POP and a server POP i.e. receiver's email server. The client i.e. the receiver opens TCP connection with receiver's POP server. This client must be authenticated first by using the user name and password. Then the client can receive the email from the mailbox.

5. Transmission Control Protocol (TCP) :

The Transmission Control Protocol is used for, 

1. Safe delivery of data.

2. Error detection.

3. Assurance of the correct sequencing of data being received.

This protocol is called connection oriented protocol because before sending the data this protocol requires that two computers have established connections. The TCP allows the transmission of arbitrary amount of data by breaking it into stream of seperate IP packets. These IP packets are numbered so that it could be reassembled properly at arrivals. Along with the data an acknowledgement is also sent/received in order to know whether the reliable connection  has occured or not.

6. User Datagram Protocol (UDP) :

The user datagram protocol is a connectionless protocol without any error detection facility. This protocol is used for simply transmission of data. The UDP is known as an unreliable protocol however this is much faster than TCP.

7. Internet Protocol (IP) :

Internet Protocol (IP) is a network layer protocol which consists of addressing information. Using this information the communication between uniquely addressed computers is possible.

There are two functionalities provided by Internet Protocol :

* Decomposition of the initial information flow into packets of standardized size and reassembling of data at the destination.

* The internet protocol routes the packet through successive networks, from the source machine to the destination which can be identified by its IP address.

Fundamental Concepts in Networking

1. Network Interface Card (NIC) :

In computer networking, a NIC provides the hardware interface between a computer and a network. A NIC basically is network adapter hardware. Ethernet supports data transfer at the rate of 10 Megabits per second (Mbps). To connect Ethernet cables to a computer, we normally use a network interface card (NIC).

2. Switch :

Switch is a device used to connect the PC to network. The switch is a device which is responsible for managing bandwidth on the network. In other words, switches are actually capable of switching the data from one port directly to the other without wasting the bandwidth of the entire network attached to that switch.

3.Router :

A Router is an electronic device used to connect two or more computers or other electronic devices to each other and usually to the Internet, by wire or radio signals. This allows several computers to communicate with each other and to the Internet at the same time.                       

Computer Networks

What is Computer Network ?

Definition : The computer network can be defined as a group of computers and other devices (such as printers, scanners, routers) connected together in order to send or receive data.

* Each of these devices in the computer network is called node. In computer network each node is connected by a wire through which the data can be moved in the form of electromagnetic waves. However there is another terminology which is commonly used in computer network and i.e. host. The host is synonym to the computer node, however there is one clear difference between node and host. Node refers to any device on the computer network and host refers to the fully functional general-purpose computer.

Components used in Networking :

* A computer network comprises the following components :

1. A minimum of at least 2 computers.

2. Cables that connect the computers to each other, although wireless communication is becoming more common.

3. A network interface device on each computer. This is called a networking interface card  or NIC.

4. A 'Switch' used to switch the data from one point to another.

5. Network operating system software.

6. You can create a computer network by hooking all the computers in your college together with cables and installing a special network interface card (an electronic circuit card that resides inside your computer popularly called as NIC) in each computer so you have a place to plug in the cable. Then you set up your computer's operating system software to establish networking. 

* Each node in the network has some unique address. These addresses help to identify the computer quickly. Addresses are assigned differently on different kinds of networks. These addresses are assigned by the organizations that are setting up the corresponding network. Typically these addresses are numeric that is easy for computers to work with,  but not for humans to remember.

Examples : 192.168.0.165

Some networks also provide names that human can more easily remember than numbers.