Open system interconnection reference model

Open system interconnection reference model

The open system interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a software application in another computer.the osi reference model is a conceptual model composed of seven layers,each specifying particular network functions.the model was developed by the interneational organization fo rstandardization (ISO) in 1984, and it is now considered they primary architectural model for intercomputer communications. Tha osi model divides the tasks involved with moving information between networked computers into even smaller, more manageable task groups.a task or group of tasks is then assigned to each of the seven osi layers.each layer is resonably self contained so that the tasks assigned to each layer can be implemented independently.this enables the solutions offered by one layer to be updated without adversely affecting the other layers.the following list details the seven layers of open system interconnecion (OSI) reference model:

·                     Layer7_____________Application

·                     Layer6_____________Presentation

·                     Layer5_____________Session

·                     Layer4_____________Transport

·                     Layer3_____________Network

·                     Layer2_____________Data Link

·                     Layer1_____________Physical

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What is the world wide web and what makes it work?

What is the world wide web and what makes it work?

The www incorporates all of the internet services abouve and much more.you can retrieve documents,view images,animation,and video,listen ot sound files,speak and hear vouce,and view programs that run on practically any software to do these things.when you log onto the internet using netscape or microsoft's internet explorer or some other browser,you are viewing documents on the world wide web.the current foundation on which the www functions is the programming language called html.it is html and other programming imbedded within html that make possible hypertext. Hypertext is teh ability to have web pages containing liks,which are areas in a page or buttons or graphics on which you can click your mouse button to retrieve another documet into your  computer.this "clickability" using hypertext links is teh feature which is unique and revolutionary about the web.

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What is Internet

What is the internet?

Tha internet is a network of networks, linking computers to computers sharing the tcp/ip protocol.each runs software to provide or "serve" infromation and /or to access and view information.the internet is the transport vehicle of r the information stored in files or documents on another computer.it can be compared to and international communications utility servicing computers.it is sometimes compared ot a giant international plumbing system.the internet itself does not contain information.it is a slight misstatement to say a "document was found on the internet." it would be more correct to say it was found through or using the internet.what it was found in (or on) is one of the computers liked to the internet.

computer on the internet may use one or all of the following intenet services.

·                     electronic mail(e-mail).permits you to send and receive mail.provides access to discussion groups.

·                     telnet or remote login.permits your computer to log onto another computer and use it as if you were there.

·                     FTP or file Transfer protocol. allows your computer to rapidly retrieve complex files intactfrom a remote computer and view or save them on your computer.

·                     Gopher. an early,text-only method for accessing internet documents.Gopher has been almost entirely subsumed in the world wide web, but you may still find gopher documents linked to in web pages.

·                     the world wide web (WWW or "the web"). the largest, fastest growing actibity on the internet.

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Storage & Memory

Storage & memory

Disks

The hard disk can store very large amounts of data (measured in megabytes), commonly,the smallest hard disks contain 1 gigabyte of information.a gigabyte is equivalent to 1000 megabytes.

Information,data and programs stored on teh hard disk are non-volatile(i.e. The information stays there even when you switch off the computer).

Remember that you can also use floppy disks, also called diskettes.there are very slow compared to hard disks and do not hold very much data.

Memory(ram)

The random access memory (ram) is the chip memory within your computer and is normally measured in megabytes.ram is the computers temporary work space.

Information, data and programs stored in ram are volatile (i.e. Teh information is lost when you switch off the computer).

Modern computers normally contain upwards of 8 megabytes.to use windows 95 and windows nt effectively you shoukd really have a minimum of 16 megabytes and as a rule of thumb,the more ram that you have tha faster your computer will seem to operate . Many home computers are supplied with 64 megabytes of memory.

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Basic units of data storage

Basic units of data storage

Bit

All computers work on a binary numbering system, i.e. They process data in one's or zero's. This 1 or 0 level of storage is called a bit.often hardware is specified as a 32 bit computer which means that the hardware can process 32 bits at a time.

Software is also described as either 16 bit or 32 bit software.

A byte consists of eight bit

Megabyte

A megabyte (mb) consists of approximately one million bytes.

Files.

Data and programs are stored on your disk in files.there are different types of files,such as the files that you store your data in and also the files that contain your programs.

Records.

A record is a collection of data held within a file.it is the sort of storage unit used by a database.for more information,

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Difference between operating system and computer programs

Difference between operating system and computer programs,

Operating system

The operating system is a special type of program that loads automatically when you start your computer.the operating system allow to use the advanced feature of a modern computer without having to learning  all the details of how the hardware works.there are a number of different types of operating system in common use.the ibm pc (personal computer) was introduced way back 1981 and was originally supplied with an operating system called dos ( disk operaing sytem). This operating system was very basic,and you had to be bit of a computer expert jus to understand how to use it.it was not user-friendly!

 

Later on microsoft introduced windows and this is the operating system that is most widely used on pcs today.

To complicate matters further, there are a number of different types of windows.teh first widely used version of windows was called windows 3.1 .thsi was more powerful than dos and fas easier to use.it had a graphical user interface(gui),i.e. you could 'drive' it using a mouse and drop down menus. Later windows nt and windows 95 were introduced. The good news is that windows 95 and windowsnt look almost identical and are boht even easier to use than windows 3.1

 

Application program

An application program is the type of programe that you use once the operating system has been loaded.examples included word processing programs, (for producing letters, memos etc), databases(for organizing large amounts of information ) and graphics programs(for producing pictures,advertisements,manuals etc).

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INPUT & OUTPUT DEVICES

Input and output devices

What are input devices?

Input decives allow you to input information to the computer and include things such as the keyboard,mouse,microphone,touchpad and joystick etc.

What are output devices?

Output devices allow you to output information from the 

computer and include the printer,speaker and the monitor.

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HARDWARE vs SOFTWARE

Hardware Vs Software

Hardware

The Terms Hardware Refers To The Physical Components Of Your Computer Such As The System Unit,Mouse ,Keyboard,Monitor,Printer,Ram,Hard Disk,Cd Rom,Floppy, Cds, Etc.

Software

The Sftware Are The Instructions That Make The Computer Work.For Instance How You Type In Words Via The Keyboard , The Software Is Responsible For Displaying The Correct Letters,In The Correct Place On The Screen . Software Is Held Either On Your Computers Hard Disk Or On A Diskette And Is Loaded(I.E. Copied) From The Disk Into The Computers Memory , As And When Required.

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Basic Concepts of I.T.

The Concept of the "Information Society"

The concept of the information society refers to the fact that it is now very easy to link computers together and access information stored on other computers.The internet is a good example . By connecting to the internet you again access to millions of other computers that are connected around the workd . You can communicate via email with anyone on this planet (assuming they also have an email connection).Unlike posting a traditional letter,this communication via email is instant! The full impact of the information society has yet to be see. In an age of instantly world wide communication it is very hard for government to maintain a grip on their population and the idea of banned books,such as the UK's attempts to stop ex-security personal disclosing embarrassing secrets begin to look a little foolish . Recently even US court decisions have been announced via internet at the same time as through more traditional means! Many companies are taking up the challenge of the information age where selling to the world via the internet can bring enormous benefits to a company.

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