Network topology ..............

Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer or biological network.Network topologies may be physical or logical.Physical topology refers to the physical design of a network including the devices, location and cable installation.

 Logical topology refers to how data is actually transferred in a network as opposed to its physical design. In general physical topology relates to a core network whereas logical topology relates to basic network.


Topology can be understood as the shape or structure of a network. This shape does not necessarily correspond to the actual physical design of the devices on the computer network. The computers on a home network can be arranged in a circle but it does not necessarily mean that it represents a ring topology.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of these links and nodes in a graph results in a geometric shape that may be used to describe the physical topology of the network.

Likewise, the mapping of the data flow between the nodes in the network determines the logical topology of the network. The physical and logical topologies may or may not be identical in any particular network.

Maintain your PC ~.~"

The tools

With Windows XP, Microsoft has done two things to make it easier to maintain a PC. It's easier to find the tools to do it with, and "Help" for using them is much better. There are two easy ways to find the tools. I recommend using "Help & Support" the first time you use the tools. The Windows Explorer route will be quicker after that.

From Windows Explorer

Open a Windows Explorer window. Right-click the "disk" (hard drive) you want to maintain. Choose "Properties". The properties dialog-box will open at the "General" tab. Click the "Disk Cleanup" button to get the "Disk Cleanup" tool.

With the properties dialog-box still open, click the "Tools" tab. You'll see the "Error-checking" and "Defragmention tools" right there.

From Help & Support

Click "Start", then "Help & Support". Enter "disk" and click the green arrow. You'll find "Using Disk Cleanup", "Using Disk Defragmenter" and "Detecting and repairing disk errors" in the left hand "Search Results" pane. Each of them will tell you how to access and use the corresponding tool.

 

1. Back up your files (and system)

The maintenance tools you're going to use are going to do some very "heavy lifting". You never know what's going to get dropped. Do yourself a big favor. Back up your critical files, and preferrably, back up your entire system first.

2. Clean up your hard drive

Start your maintenance work with Disk Cleanup. It will make error checking and defragmenting go better and faster, because there's less junk for the tools to deal with. You might want to go further and do some basic cleanup before you start the rest of your maintenance. PC World has two good articles on this topic. [one] [two]
Deleting program files is an error that neophytes often make. Programs should always be uninstalled, which is quite different. To uninstall use: "Start" > "Control Panel" > "Add and Remove Programs". Find the program in the list and delete it. After you've done that, some files may remain in the program's folder, which is usually in C:\Program Files\Name (name of the program you just installed). It's OK to delete the files and folder now.

3. Detect and repair disk errors

Disk error checking was called ScanDisk in Windows 98. It's a good idea to check for errors about once a month to keep your system running well. The tool can find and fix errors in the file allocation table, the file system structure (lost clusters, crosslinked files) and the directory tree structure. It can also detect and isolate sectors that have gone bad because of damage to the surface of your disk.
When you click "Start" the tool will tell you, "The disk check could not be performed... Do you want to schedule this disk check to occur the next time you restart the computer? Click "Yes".
If you begin to see defective sectors in the report, especially a growing number, you may want to replace your hard drive before it crashes and dies. At the very least bad sectors should motivate you to be very disciplined about backing up your work.

4. Defragment your hard drive

You should defragment your hard drive on a regular basis -- every three months is good -- to keep your system running well. In the course of normal usage, files are constantly changed and written or rewritten to the hard drive. The file system tries to pack the files tightly. It breaks them into pieces to fit where it finds space for them. Over time these pieces get scattered all over the drive. It begins to take a lot of head movement (and thus time) to read and write files. As a result, your computer's performance suffers, and worse yet, it's easier for errors to creep in.

Before you defrag

• Clean out any junk files that you don't need. Empty the recycle bin, delete the contents of C:\Temp\ and C:\Windows\Temp, and delete your temporary internet files ["Tools" > "Internet Options" > "Delete files..."]. You might want to use Disk Cleanup to clean out more junk.
• If you have a virus program, turn off "auto-protect" or close the program. Otherwise it will very likely interfere with Disk Defragmenter.
• Disable your screensaver Right click the Desktop > select "Properties" > click the "Screen Saver" tab > select "none" > and click "OK".
• You may need to disable, or exit other programs too. (Use the "3-fingered salute" -- Ctrl+Alt+Delete -- to shut down unnecessary programs.)
• It's a good idea to check your disk for errors just before you defrag. The defrag tool will look for disk errors but it can't fix them itself. If there are errors, you'll end up using the error checking tool, and trying defrag again.

Do not run defrag if there's a chance that electrical power will be interrupted -- for example, during a thunderstorm, or when construction could cause an outage. Defrag will be unable to complete what it was in the middle of and your hard drive will probably be scrambled.
Don't use the automatic mode to defrag a laptop. Some day you're going to forget to plug it in, defrag will start, the battery will run down, and you'll lose all your data and get to reinstall everything.

5. Good housekeeping

Cleaning your PC is part of the maintenance job. Computers aren't big enough for dust bunnies, but they collect a lot more fuzz than you might imagine. It can eventually cause overheating, which is a nemesis for anything electronic. The page on cleaning your PC will help you with this and other "housekeeping" chores.

 

Computer Topics !!!

Get to know your PC

You need to be uninhibited if you want to learn more about using your PC. That's how kids learn to use them so quickly.
"Right-click" is one safe way to explore your PC. Right-click on anything and everything. Right-click means click an object with the right mouse button -- for example, this text -- try it and see what you get.

It's not going to hurt anything. It merely opens a context menu, which is simply a list of options appropriate for the object you right-clicked. Try clicking more objects up at the top of your browser.
Nothing happens until you "left-click" one of the menu options. If you're in doubt about clicking any of them, just left-click anywhere outside the menu and it will close. It's always safe to click "Properties", which gives you access to lots of information and settings.

Have a look around when "Properties" opens. There's always a "Cancel" button that will bail you out of "Properties" with no changes and no damage done. If you do make changes it could adversely affect your computer if you don't know what you're doing.

Start your computers.

Microsoft calls it "starting" your computer, but it's still "boot" to me. Don't confuse "starting" with the "Start" menu. Starting is turning on, starting , or booting your computer. The "bootstrap" method of loading the operating system into computer memory was invented about the same time electronic computers were invented.

I remember loading the first 17 "words" by hand to start one of the first computers I used. Each word was 2 bytes, or 16 bits. You had to set 16 switches and press the 17th to load each word. Using those 17 words (not switches), the computer was able to load another 1000 or so words on its own. They were on a strip of paper tape with holes punched in it -- much like a miniature player piano roll. Primed with those 1000 words, the computer was then able to load the rest of the operating system from a cassette tape.
It took me about 3 minutes to manually boot that old computer. Windows is loaded in a similar way. [more | more yet ] Too bad the process still takes so long, but there is a way to avoid booting your computer every day. The concept has been updated for Windows Vista.

Computing

The basic principles of general purpose computers have not changed since they were first conceived by Charles Babbage sometime before 1833. (His design was not actually built until sometime around 1990 -- yes those dates are correct.)

Computer principles don't change because they are as fundamental as mathematics, which of course don't change either. We're now close to the 60th anniversary of the first electronic computer, which was based on Babbage's original design. The big difference is they are powered by electricity, not steam.
Computer principles are embodied in the primary elements of a computer: input device(s), store (memory), processor, instructions and output device(s). In the beginning there were no hard drives, keyboards or monitors, much less mice. But they fundamentally worked in the same way.
Computer operation is straightforward -- data goes in (input) -- operations on the data are performed, results are stored (intermediate and final) -- the results come out (output). All of this is under the control of instructions (program), which are just another form of data.
For example -- [(2+4) divided by 3]. First the two numbers <2> and <4> are go in. They are added together and the temporary results are stored. The number <3> is then goes in. Next the temporary results <6> are divided by <3> and the results <2> come out. And it's all done in less than a millionth of a second.

The confusing thing about a PC is the multiplicity of input devices, memories, instruction sets, processors and output devices -- most of which are themselves used for multiple functions and tasks in turn. The keyboard, mouse, CD drives, modems and cameras are all input devices. Speakers, printers, the monitor, and modems (again) are common output devices.
Memory is used not only for data and results, but also for instructions. That's where it really gets confusing. The processor can't perform an instruction unless both the current data and the current instruction are in memory.

PCs work with much more data than memory can hold. That's why hard drives were invented. They "store" the data of the past (results), the data of the future (input), and instructions not currently being used. The processor goes to the hard drive to "fetch" data and instructions it needs next, and to "store" results it has completed.

Files

There are two primary types of files used by computers: instruction files and data files. Instruction files are either system (i.e., Windows) or program files. They instruct the processor to store input data, perform operations on the data, and output the results.
Data files may be in the form of documents, object files, data tables, output data or system data. Sound files and image files are examples of object files. Font files are an example of data table files. The "Registry" is the prime example of Windows system data.
All these file types -- data, system, and program -- are mixed together on the hard drive. They are segregated by location (folders) to a large extent, but it's somewhat of a mess. If you want to use a computer effectively, it's a big help to keep the files organized on your computer.
Windows Explorer is your window into the files on your computer. It gives you the big picture, yet you can zoom in and get things done quickly. There are some things you can't do any other way in fact.
Opening a file is a simple example of the efficiency of Windows Explorer. If you navigate to a file with Windows Explorer, a simple "double-click" will open the right program, which will then open the file. The other way is to open the program and then use it's less convenient navigation to open the file.

Backup

Backup is a chore, and people don't like to do chores. You're not likely take backup seriously until you've lost something irreplaceable -- maybe after it's happened twice. A wise person learns from the mistakes of other people though. Our backup pages should help you design and follow a backup strategy that fits your situation.

Computer myths

The most common PC myths are Windows myths. One of the most common is about how Windows uses memory. They persist because they seem logical. Most are relatively harmless, but they cause people to waste time, energy and money.

The virus myth: "You get a computer virus when you download a file to your hard drive". Truth is, not really. Yes, it's like a land mine -- harmless if left alone, but deadly if activated. If you open or install the infected file, the virus will be activated. But it can't do any harm until then.

The preview pane in Outlook Express (or Outlook) provides the grain of truth that perpetuates the download myth. Simply viewing an email in the preview pane can activate malevolent content (a virus or worm). Downloading the message caused no harm -- it's the preview pane that uncorks the content.

Do You Know hOw to maNage oUr pC ? ^_^

If you rarely go online, observe at least basic security precautions and occasionally install new programs, your computer will probably not give you any real trouble.
It's also possible to use your computer very heavily, install and uninstall all sorts of programs, go online extensively, and still avoid real trouble. That is, if you do most of the right things most of the time. (None of us are perfect, eh?)

1. Get serious about online security

How long do you think it takes before an unprotected computer is succesfully attacked? Experiments have shown that it's usually less than 15 minutes (when using a broadband connection).

These days, new PCs come with the Windows Firewall turned on. That's good, but there are many sophisticated attacks that you need to defend against too. You need a comprehensive online defense system to protect your PC over the long term.

2. Get serious about regular backups

Backup is a personal thing. Most of us have "stuff on our computer" that we'd hate to lose -- photos, correspondence, family trees, business records -- things like that. Many of us also invest considerable effort getting our computers set up just the way we like them. We'd hate to lose all that work too. Your backup strategy should depend on what you have at risk and what you're willing to lose.

Backup is insurance. Yes, it costs something -- time, effort and perhaps a little money to get the insurance. It also takes discipline, but backup is the only way to make sure you won't lose the things that are most important to you. The question is not if something will go wrong, but when will it go wrong. Backup can be insurance against little mistakes, and against disaster.

First, do some analysis to decide what you want to back up. Then put the right process and tools in place so that you can do it effectively.

3. At least get interested in housekeeping

The performance of your PC will gradually decline, or it can even become inoperable without some basic maintenance. There's also some basic cleanup you can do that even a new computer can benefit from.
After that general pruning, there are five things -- eliminate spyware, delete unused files, scan your hard drive for errors, defragment your hard drive, and some physical housekeeping -- that you should do once in a while to keep your computer healthy.

IntRodDctIoN tO CloUd cOmPutiNg A_A"

The two words in the phrase cloud computing have the following interpretations:

• Cloud :

As a noun, this is a metaphor for the Internet. and as an adjective it means pertaining to the Internet . This usage derives from the cloud symbols that represent the Internet on diagrams.

• Computing:

Any IT activity carried out by an entity:

• When using "a local server or a personal computer", which implies that the IT resources are under the exclusive control of the entity.
• To "store, manage, and process data", which implies that the data is private to the entity, in the sense that it is determined by them, even if it is accessible by others.

This means that cloud computing is a type of Internet-based computing, and it consists of every situation where the use of IT resources by an entity has all of the following characteristics:

• Access to the resources is:
  • Controlled by the entity, and restricted by them to their authorised users.
  • Delivered via the Internet to all of these users.
• The resources are:
  • Hosted by a service provider on behalf of the entity.
  • Dedicated to the exclusive use of the entity.
• Data processed by the resources is:
  • Private to the entity and its associates.
  • Entered or collected by them, or automatically produced for them.

Depending on the context, cloud computing can mean:

• Access to and use of the resources.
• The hosting and delivery service that provides this access.
• A model for enabling such access and delivery.
• The hosted resources or services themselves.
• The computing execution carried out by the services.
• Technology used for the provision of the services.

CloUd ComPuTing ^~^

Cloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a utility (like the electricity grid) over a network (typically the Internet).

Cloud computing entrusts, typically centalized, services with your data, software, and computation on a published application programming interface (API) over a network. It has a lot of overlap with software as a service (SaaS).

End users access cloud based applications through a web browser or a light weight desktop or mobile app while the business software and data are stored on servers at a remote location. Cloud application providers strive to give the same or better service and performance than if the software programs were installed locally on end-user computers.

At the foundation of cloud computing is the broader concept of infrastructure convergence (or Converged Infrastructure) and shared services. This type of data centre environment allows enterprises to get their applications up and running faster, with easier manageability and less maintenance, and enables IT to more rapidly adjust IT resources (such as servers, storage, and networking) to meet fluctuating and unpredictable business demand.

What Functions Can the iPad Handle?

A person who takes an Apple iPad out of the package and has it properly activated can take advantage of a large number of different functions. Here are just a few of the things that anyone can do with the iPad when it is being handled.

• It is incredibly easy to get onto with a Wi-Fi or 3G network. The Safari web browser, which is a commonly used web browser on Apple products, can be used on the iPad. This browser is easy to control and can allow a person to go onto any website that one wants to use.

Of course, the 3G network connectivity is not going to be available on every single iPad. However, the speeds that are going to work with the 3G connection can be faster than that of what one might already be getting off of a regular iPad with a Wi-Fi connection.

• Email functionality is a plus. The device can handle email through all types of online email clients. This is used through not only the Safari web browser but also through a virtual keyboard that can come up on the iPad when a message has to be entered in. The use of this function will make for a convenient and handy process that any iPad user can enjoy.

• Videos can be viewed with ease. People can upload video files from a computer to the iPad through a simple USB connection that can work on the main computer. The 9.7 diagonal inch screen will provide for a great space for a person to view videos on. In fact, the iPad has such a large hard drive that can handle sixteen or more gigabytes on it that it will work to handle even the largest video applications one might have.

• It can play music as well. The iPad can play music files from many formats including the MP3 and Apple Lossless formats. It can also get new music online through the iTunes software program that is inside of the iPad.

• Finding YouTube videos is easy to do with the iPad. The device has its very own YouTube channel. It is one that was designed especially with the iPad in mind.

• Photos are easy to view on the iPad. The high resolution screen with automatically adjustable brightness controls can get all types of pictures to be played. The pictures on the iPad can be moved into different folders and slideshows as well. This is great for those who want to get presentations created.

• Organization standards are also available. There are many organizational tools that are used on the iPad including a calendar, an address book and a notepad. All of these functions can save all types of personal data onto a notepad without too many concerns about what is working.

• 
  
  Maps are great to find on the iPad. The iPad uses Google Maps technology to find maps of all sorts of different places from all around the world. Street view functions like what can be found through Google Earth are also available. Street directions can also be found on the device, thus making this perfect for those who need to find directions when driving. The fact that the iPad can find a user’s position through a GPS reader will make this even more convenient.