Common features

Process management

Interrupts

Memory management

Virtual file system

Device drivers

Networking

Security

Graphical user interfaces

v • d • e

An operating system (OS) is an interface between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of the computer that acts as a host for computing applications run on the machine. As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications. Almost all computers (including handheld computers, desktop computers, supercomputers, video game consoles) as well as some robots, domestic appliances (dishwashers, washing machines), and portable media players use an operating system of some type.[1] Some of the oldest models may, however, use an embedded operating system that may be contained on a data storage device.

Operating systems offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By invoking these interfaces, the application can request a service from the operating system, pass parameters, and receive the results of the operation. Users may also interact with the operating

system with some kind of software user interface like typing commands by using command line interface (CLI) or using a graphical user interface (GUI, commonly pronounced “gooey”). For hand-held and desktop computers, the user interface is generally considered part of the operating system. On large multi-user systems like Unix and Unix-like systems, the user interface is generally implemented as an application program that runs outside the operating system. (Whether the user interface should be included as part of the operating system is a point of contention.)

Common contemporary operating systems include BSD, Darwin (Mac OS X), Linux, SunOS (Solaris/OpenSolaris), and Windows NT (XP/Vista/7). While servers generally run Unix or some Unix-like operating system, embedded system markets are split amongst several operating systems,[2][3] although the Microsoft Windows line of operating systems has almost 90% of the client PC market.

Functions Of Operating System           SSSSSS        Today most operating systems perform the following important functions:1. Processor management, that is, assignment of processor to different tasks being performed by the computer system.2. Memory management, that is, allocation of main memory and other storage areas to the system programmes as well as user programmes and data.3. Input/output management, that is, co-ordination and assignment of the different output and input device while one or more programmes are being executed.4. File management, that is, the storage of file of various storage devices to another. It also allows all files to be easily changed and modified through the use of text editors or some other files manipulation routines.

5. Establishment and enforcement of a priority system. That is, it determines and maintains the order in which jobs are to be executed in the computer system.6. Automatic transition from job to job as directed by special control statements.7. Interpretation of commands and instructions. 8. Coordination and assignment of compilers, assemblers, utility programs, and other software to the various user of the computer system.9. Facilities easy communication between the computer system and the computer operator (human). It also establishes data security and integrity

Functions Of Operating System                   Today most operating systems perform the following important functions:1. Processor management, that is, assignment of processor to different tasks being performed by the computer system.2. Memory management, that is, allocation of main memory and other storage areas to the

system programmes as well as user programmes and data.3. Input/output management, that is, co-ordination and assignment of the different output and input device while one or more programmes are being executed.4. File management, that is, the storage of file of various storage devices to another. It also allows all files to be easily changed and modified through the use of text editors or some other files manipulation routines.

5. Establishment and enforcement of a priority system. That is, it determines and maintains the order in which jobs are to be executed in the computer system.6. Automatic transition from job to job as directed by special control statements.7. Interpretation of commands and instructions. 8. Coordination and assignment of compilers, assemblers, utility programs, and other software to the various user of the computer system.9. Facilities easy communication between the computer system and the computer operator (human). It also establishes data security and integrity

Functions Of Operating System                   Today most operating systems perform the following important functions:1. Processor management, that is, assignment of processor to different tasks being performed by the computer system.2. Memory management, that is, allocation of main memory and other storage areas to the system programmes as well as user programmes and data.3. Input/output management, that is, co-ordination and assignment of the different output and input device while one or more programmes are being executed.4. File management, that is, the storage of file of various storage devices to another. It also allows all files to be easily changed and modified through the use of text editors or some other files manipulation routines.

5. Establishment and enforcement of a priority system. That is, it determines and maintains the order in which jobs are to be executed in the computer system.6. Automatic transition from job to job as directed by special control statements.7. Interpretation of commands and instructions. 8. Coordination and assignment of compilers, assemblers, utility programs, and other software to the various user of the computer system.9. Facilities easy communication between the computer system and the computer operator (human). It also establishes data security and integrity

In computing, a system call is the mechanism used by an application program to request service from the operating system based on the monolithic kernel or to system servers on operating systems based on the microkernel-structure.

Contents

[hide]

1 Background 2 The library as an intermediary 3 Examples and tools 4 Typical implementations 5 Types Of System Call 6 References 7 External links

[edit] Background

A system call is a request made by any program to the operating system for performing tasks—picked from a predefined set—which the said program does not have required permissions to execute in its own flow of execution. System calls provide the interface between a process and the operating system. Most operations interacting with the system require permissions not available to a user level process, e.g. I/O performed with a device present on the system or any form of communication with other processes requires the use of system calls.

The fact that improper use of the system call can easily cause a system crash necessitates some level of control. The design of the microprocessor architecture on practically all modern systems (except some embedded systems) offers a series of privilege levels -- the (low) privilege level in which normal applications execute limits the address space of the program so that it cannot access or modify other running applications nor the operating system itself. It also prevents the application from directly using devices (e.g. the frame buffer or network devices). But obviously many normal applications need these abilities; thus they can call the operating system. The operating system executes at the highest level of privilege and allows the applications to request services via system calls, which are often implemented through interrupts. If allowed, the system enters a higher privilege level, executes a specific set of instructions which the interrupting program has no direct control over, then returns control to the former flow of execution. This concept also serves as a way to implement security.

With the development of separate operating modes with varying levels of privilege, a mechanism was needed for transferring control safely from lesser privileged modes to higher privileged modes. Less privileged code could not simply transfer control to more privileged code at any point and with any processor state. To allow it to do so would allow it to break security. For instance, the less privileged code could cause the higher privileged code to execute in the wrong order, or provide it with a bad stack.

[edit] The library as an intermediary

Generally, systems provide a library that sits between normal programs and the operating system, usually an implementation of the C library (libc), such as glibc. This library exists between the OS and the application, and increases portability.

On exokernel based systems, the library is especially important as an intermediary. On exokernels, libraries shield user applications from the very low level kernel API, and provide abstractions and resource management.

[edit] Examples and tools

On Unix, Unix-like and other POSIX-compatible Operating Systems, popular system calls are open, read, write, close, wait, exec, fork, exit, and kill. Many of today's operating systems have hundreds of system calls. For example, Linux has 319 different system calls. Similarly, FreeBSD has almost 330.

Tools such as strace and truss allow a process to execute from start and report all system calls the process invokes, or can attach to an already running process and intercept any system call made by said process if the operation does not violate the permissions of the user. This special ability of the program is usually also implemented with a system call, e.g. the GNU's strace is implemented with ptrace().

[edit] Typical implementations

Implementing system calls requires a control transfer which involves some sort of architecture-specific feature. A typical way to implement this is to use a software interrupt or trap. Interrupts transfer control to the OS so software simply needs to set up some register with the system call number they want and execute the software interrupt.

For many RISC processors this is the only feasible implementation, but CISC architectures such as x86 support additional techniques. One example is SYSCALL/SYSENTER, SYSRET/SYSEXIT (the two mechanisms were independently created by AMD and Intel, respectively, but in essence do the same thing). These are "fast" control transfer instructions that are designed to quickly transfer control to the OS for a system call without the overhead of an interrupt. Linux 2.5 began using this on the x86, where available; formerly it used the INT instruction, where the system call number was placed in the EAX register before interrupt 0x80 was executed.[1]

An older x86 mechanism is called a call gate and is a way for a program to literally call a kernel function directly using a safe control transfer mechanism the OS sets up in advance. This approach has been unpopular, presumably due to the requirement of a far call which uses x86 memory segmentation and the resulting lack of portability it causes, and existence of the faster instructions mentioned above.

For IA64 architecture, EPC (Enter Privileged Mode) instruction is used. The first eight system call arguments are passed in registers, and the rest are passed on the stack.

[edit] Types Of System Call

System calls can be roughly grouped into five major categories:

1. Process Control.

end, abort load, execute create process, terminate process get process attributes, set process attributes wait for time wait event, signal event allocate and free memory

2.File management.

create file, delete file open, close read, write, reposition get file attributes, set file attributes

3. Device Management.

request device, release device read, write, reposition get device attributes, set device attributes logically attach or detach devices

4. Information Maintenance.

get time or date, set time or date get system data, set system data get process, file, or device attributes set process, file, or device attributes

5. Communication.

create, delete communication connection send, receive messages transfer status information attach or detach remote devices

A wizard is a user interface element where the user is presented with a sequence of dialog boxes. Through these dialog boxes, the user is led through a series of steps, performing tasks in a specific sequence. Sometimes it may be easier to perform tasks using a wizard, especially for complex or infrequently performed tasks where the user is unfamiliar with the steps involved.

By 2001, wizards had become commonplace in most consumer-oriented operating systems, though not necessarily by the same name. In Mac OS X, for example, they are

called "Assistants"; some examples include the "Setup Assistant", which is run when one boots the Macintosh for the first time, and the "Network Setup Assistant", which has similar function to the aforementioned "New Connection Wizard". GNOME also has a similar construct called Druids.

Web applications , such as an airline booking site, also make use of the wizard paradigm to complete lengthy interactive processes. Oracle Designer also uses wizards extensively.

By contrast, expert systems guide the user through a series of (usually yes/no) questions to solve a problem, and tend to make use of artificial intelligence or other complex algorithms. Some consider expert systems as a general category that includes all problem-solving programs including wizards.

Wizards were controversial among user interface designers when they first gained widespread use. This controversy centered around the fact that wizards encourage modal windows, which its opponents consider antithetical to proper human interface design.

Microsoft Manual of Style for Technical Publications (Version 3.0) urges technical writers to refer to these assistants as "wizards" and to use lowercase letters. In countries where the concept of wizard does not convey the idea of helpfulness or is offensive, the manual suggests using the term "assistant" instead.

When you improperly shut down your computer does it harm your computer

hardware, or anything else in your computer?

I had found 2 views on this topic.Hope you fing them useful....

By http://askthegeek.kennyhart.com/

by "improperly shut down," I assume you mean pressing the power button instead

of clicking Start->Shut Down from Windows. This won't harm any of your

hardware. After all, Windows powers off the PC, too, when you do a "normal"

shutdown. Think of it this way: Your computer is made from components similar to

those in any other electronic device--like a stereo or TV--and you turn them on and

off all the time without any bad effects. However, the data on your hard drive can

be damaged by an improper shutdown.

This was a big problem back in the days of Windows 95 and 98. When you

restarted after an improper shutdown, the operating system would come up

asking you to run scandisk to correct hard disk errors. It's not as big a problem

with Windows XP, but it does happen. If you remove power from the system while

data is being written to your hard disk, the data will be incomplete and appear

corrupt. Usually, though, a system hang severe enough to warrant pushing the

power button is the result of a problem reading or loading a file and your PC won't

suffer any ill effects if you power it down. By Syschat.com

What is the significance of proper shut down? If an improper shut down occurs

(probably due to a power supply failure, pulled plug, or the user just didn’t know how

to use the computer), your registry files are forced to stop its operation without

saving your recent works and other necessary settings that have been changed. In

order to save works, make sure that before turning off your pc, you have saved your

current work. In windows, after saving all the changes, a turn off button is pressed to

finally confirm the shut down process. If you just want to reboot your computer,

there is also a restart button for this. Also take note that once you have initiated the

machine to shut down, do not turn off or pull the power plug of the device

immediately unless your computer has literally stopped running. This is usually

noted if the monitor has no more output and the mouse and keyboard input

response have stopped.

A possible unsuccessful system restore is another disadvantage brought forth by an

improper or illegal shut down. For those who don’t know about system restore, it is a

windows component that enables computers to be restored to a previous state.

System restore automatically creates restore points daily. If an improper shut down

occurs during the process of a system restore, an inconsistency into the changed log

occurs. This affects the whole restoration process, thus being unsuccessful.

Whenever an improper shut down occurs, the computer automatically initiates disk

check up as soon as it reboots. It is strongly recommended that you let the

computer scan its disk for system errors because these mentioned errors, as well as

lost data files and files not in proper location are the basic effects of an improper

shut down. These unwanted bad sectors may soon cause your computer to have

decreased level of performance and efficiency.

Another harmful effect of an improper shut down that may be considered as fatal is

the hardware failure. 2 of the most significant parts of a hard disk are the platters

and the read write head. The platters are coated with magnetic substances used for

recording data while the read write head examines or alters the data. The data

manipulation and examination is done through constant rubbing of the platters and

the read write head. During proper shut down process, the hard disk’s rotating

platters slows down until it stops. If an improper shut down occurs, the rotating

platters stop in an abrupt manner. This causes unwanted scratches on the platters.

And these scratches may have drastic effects on the hard disk’s performance

Will an improper shutdown harm my computer?

I get this question often enough that it's time

for a detailed post. Today, I'm answering

Valania's question:

 

When you improperly shut down your computer does it harm your computer

hardware, or anything else in your computer?

Valania, by "improperly shut down," I assume you mean pressing the power

button instead of clicking Start->Shut Down from Windows. This won't

harm any of your hardware. After all, Windows powers off the PC, too, when

you do a "normal" shutdown. Think of it this way: Your computer is made

from components similar to those in any other electronic device--like a

stereo or TV--and you turn them on and off all the time without any bad

effects. However, the data  on your hard drive can be damaged by an

improper shutdown.

This was a big problem back in the days of Windows 95 and 98. When you

restarted after an improper shutdown, the operating system would come up

asking you to run scandisk to correct hard disk errors. It's not as big a

problem with Windows XP, but it does happen. If you remove power from

the system while data is being written to your hard disk, the data will be

incomplete and appear corrupt. Usually, though, a system hang severe

enough to warrant pushing the power button is the result of a problem

reading or loading a file and your PC won't suffer any ill effects if you power

it down.

Cheers!

The Geek

Technorati tags: shutdown, system hang, data loss

POSTED BY KENNY HART AT 2:20 PM

1 C O M M E N T S :

 Anonymous said...

Thanks Geek,

I was quite worried over this for a while. Actually my UPS is not functioning

properly, and power supply also flactuates quite often, so my PC restarts

again and again.

Now, I think I don't need to worry that my PC is getting harmed.

Thanks for inputs

1:32 PM

SYMPTOMS

CAUSE

RESOLUTION

MORE INFORMATION

o Windows 98, Windows 98 Second Edition, or Windows Millennium (Me)

o Windows 95 OSR2, Windows 98, or Windows 98 Second Edition

Expand all | Collapse all

SYMPTOMS

AN UNMANAGED SHUTDOWN CAN OCCUR DUE TO A POWER INTERRUPTION OR FAILURE, A BSOD, OR THE PRESSING OF THE

SYSTEM RESET OR POWER BUTTON. AN UNSTABLE SYSTEM CAN ALSO LEAD TO AN IMPROPER WINDOWS SHUTDOWN. SOME

OF THE CAUSES OF AN UNSTABLE SYSTEM ARE:

OVERCLOCKING

SYSTEM MEMORY ERRORS DUE TO BAD OR INCOMPATIBLE MEMORY

INSUFFICIENT WATTAGE FROM THE POWER SUPPLY

UNSTABLE BIOS

BAD SYSTEM COMPONENTS, I.E. MOTHERBOARD, CPU, PSU, MODEMS, VIDEO CARDS, ETC.

BAD OR IMPROPER DRIVERS

AFTER AN IMPROPER SHUTDOWN OCCURS AND THE COMPUTER IS RESTARTED THE RAID CONTROLLER WILL RECOGNIZE

THAT AN IMPROPER SHUTDOWN HAS OCCURRED. A SPECIAL RECOVERY PROCESS MAY BE REQUIRED TO VERIFY THAT NO

DATA CORRUPTION HAS OCCURRED AND DATA REDUNDANCY HAS BEEN PROPERLY MAINTAINED.

THE TYPE OF RECOVERY PROCESS DEPENDS ON THE RAID LEVEL. ALL THE RECOVERY PROCESSES LISTED IN TABLE A WILL

HAVE A SIGNIFICANT NEGATIVE IMPACT ON PERFORMANCE. THE TIMES WILL BE THE SAME REGARDLESS OF THE AMOUNT OF

DATA ON THE VOLUMES

Unclean Shutdowns

When a system is properly shut down, all memory-based file system changes are written to disk and the file systems on disk are marked as being clean. However, if an improper shutdown (for example, a power failure) occurs, the memory-based information might not be written to disk and therefore certain file systems will not have their “clean” flag set (because, in fact, they might have structural problems as a result of the memory-based information not being written to disk).

When this happens, a special activity occurs during the boot process. The file system consistency checker (fsck), when checking for clean flags on all file systems represented in the file /etc/fstab, will detect that file systems exist that do not have clean flags set. For these file systems, fsck will perform a check/repair operation to locate and fix any problems that resulted from the improper shutdown. In nearly all cases, fsck can find and fix all of the structural problems and the file system can then be marked clean.

On rare occasions, the file system corruption is beyond what fsck can automatically correct. In these cases fsck will terminate with an error message indicating that you need to use it in an interactive mode to fix the more serious problems. In these cases data loss is likely. Before using fsck in interactive mode, try to back up any critical files by moving them to another file system or backing them up to tape, if a back-up copy of them does not already exist.

For a more detailed discussion of using fsck to repair file systems, refer to the following manpages:

fsck (1M)

Types of Operating SystemsWithin the broad family of operating systems, there are generally four types, categorized based on the types of computers they control and the sort of applications they support. The categories are:

Real-time operating system (RTOS) - Real-time operating systems are used to control machinery, scientific instruments and industrial systems. An RTOS typically has very little user-interface capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use. A very important part of an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time, every time it occurs. In a complex machine, having a part move more quickly just because system resources are available may be just as catastrophic as having it not move at all because the system is busy.

Single-user, single task - As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld computers is a good example of a modern single-user, single-task operating system.

Single-user, multi-tasking - This is the type of operating system most people use on their desktop and laptop computers today. Microsoft's Windows and Apple's MacOS platforms are both examples of operating systems that will let a single user have several programs in operation at the same time. For example, it's entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the Internet while printing the text of an e-mail message.

Multi-user - A multi-user operating system allows many different users to take advantage of the computer's resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.

Photo courtesy Apple

Mac OS X Panther screen shot

It's important to differentiate between multi-user operating systems and single-user operating systems that support networking. Windows 2000 and Novell Netware can each support hundreds or thousands of networked users, but the operating systems themselves aren't true multi-user operating systems. The system administrator is the only "user" for Windows 2000 or Netware. The network support and all of the remote user logins the network enables are, in the overall plan of the operating system, a program being run by the administrative user.

With the different types of operating systems in mind, it's time to look at the basic functions provided by an operating system.

Previous Page Next Page

When you turn on your computer, it's nice to think that you're in control. There's the trusty computer mouse, which you can move anywhere on the screen, summoning up your music library or Internet browser at the slightest whim. Although it's easy to feel like a director in front of your desktop or laptop, there's a lot going on inside, and the real man behind the curtain handling the necessary tasks is the operating system.

Most desktop or laptop PCs come pre-loaded with Microsoft Windows. Macintosh computers come pre-loaded with Mac OS X. Many corporate servers use the Linux or UNIX operating systems. The operating system (OS) is the first thing loaded onto the computer -- without the operating system, a computer is useless.

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Operating System FunctionsAt the simplest level, an operating system does two things:

1. It manages the hardware and software resources of the system. In a desktop computer, these resources include such things as the processor, memory, disk space and more (On a cell phone, they include the keypad, the screen, the address book, the phone dialer, the battery and the network connection).

2. It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.

The first task, managing the hardware and software resources, is very important, as various programs and input methods compete for the attention of the central processing unit (CPU) and demand memory, storage and input/output (I/O) bandwidth for their own purposes. In this capacity, the operating system plays the role of the good parent, making sure that each application gets the necessary resources while playing nicely with all the other applications, as well as husbanding the limited capacity of the system to the greatest good of all the users and applications.

©2008 HowStuffWorksThe operating system controls every task your computer

carries out and manages system resources.

The second task, providing a consistent application interface, is especially important if there is to be more than one of a particular type of computer using the operating system, or if the hardware making up the computer is ever open to change. A consistent application program interface (API) allows a software developer to write an application on one computer and have a high level of confidence that it will run on another computer of the same type, even if the amount of memory or the quantity of storage is different on the two machines.

Even if a particular computer is unique, an operating system can ensure that applications continue to run when hardware upgrades and updates occur. This is because the operating system -- not the application -- is charged with managing the hardware and the distribution of its resources. One of the challenges facing developers is keeping their

operating systems flexible enough to run hardware from the thousands of vendors manufacturing computer equipment. Today's systems can accommodate thousands of different printers, disk drives and special peripherals in any possible combination.

Multi-user and Multitasking

Although some operating systems only serve the needs of individual users, others must service hundreds of workers in large businesses. These multi-user operating systems are especially proficient at giving employees the ability to share resources such as printers or memory.

Today, many operating systems have multitasking capabilities. They can run several programs at once, and monitor each process. A process is a program that is currently running.

What is a single-user operating system?We are all familiar with the concept of sitting down at a computer system and writing documents or performing some task such as writing a letter. In this instance there is one keyboard and one monitor that you interact with.

Operating systems such as Windows 95, Windows NT Workstation and Windows 2000 professional are essentially single user operating systems. They provide you the capability to perform tasks on the computer system such as writing programs and documents, printing and accessing files.

Consider a typical home computer. There is a single keyboard and mouse that accept input commands, and a single monitor to display information output. There may also be a printer for the printing of documents and images.

In essence, a single-user operating system provides access to the computer system by a single user at a time. If another user needs access to the computer system, they must wait till the current user finishes what they are doing and leaves.

Students in computer labs at colleges or University often experience this. You might also have experienced this at home, where you want to use the computer but someone else is currently using it. You have to wait for them to finish before you can use the computer system.

 

What is a multi-user operating system?A multi-user operating system lets more than one user access the computer system at one time. Access to the computer system is normally provided via a network, so that users access the computer remotely using a terminal or other computer.

In the early days of large multi-user computers, multiple terminals (keyboards and associated monitors) were provided. These terminals sent their commands to the main multi-user computer for processing, and the results were then displayed on the associated terminal monitor screen. Terminals were hard-wired directly to the multi-user computer system.

Today, these terminals are generally personal computers and use a network to send and receive information to the multi-user computer system. Examples of multi-user operating systems are UNIX, Linux (a UNIX clone) and mainframes such as the IBM AS400.

The operating system for a large multi-user computer system with many terminals is much more complex than a single-user operating system. It must manage and run all user requests, ensuring they do not interfere with each other. Devices that are serial in nature (devices which can only be used by one user at a time, like printers and disks) must be shared amongst all those requesting them (so that all the output documents are not jumbled up). If each user tried to send their document to the printer at the same time, the end result would be garbage. Instead, documents are sent to a queue, and each document is printed in its entirety before the next document to be printed is retrieved from the queue. When you wait inline at the cafeteria to be served you are in a queue. Imagine that all the people in the queue are documents waiting to be printed and the cashier at the end of the queue is the printer

The functions of devices attached. with the computer are controlled by the special system software called device drivers. The device driver tells the operating system how to communicate with a device. Each device has its own device driver. When you boot a computer, the operating system loads each device’s driver. If you attach a new device or hardware such as scanner to computer then you have to install its driver. Usually the operating system has the built-in device drivers for commonly used input/output devices such as mouse, keyboard, etc. The operating system automatically installs these drivers.

The Windows clipboard is used to temporarily store stuff. This "stuff" can come in the form of just about anything. Images, files, documents, etc.—they can all be placed on the clipboard. Once something has been copied to the clipboard it can be pasted into another location.

The clipboard isn't a program you can actually access and play with. It's a built-in windows component that works transparently. When you copy or cut, the info is put onto this clipboard. When you paste, the information that's on the clipboard is put into whatever it is you're working on.

For instance, if I have some information on a web page that I want to put into a word processing document, this is what would happen:

1. I highlight and copy (CTRL-C) the text from the web page. When I do this, the text is placed on the clipboard.

2. Now, I open my word processor (MS Word 2000 and up must be open before you copy). Right now, the info is still sitting on the clipboard and can be pasted into my word processor or any other program that can handle text.

3. OK, now I right-click a blank area of my word processing document and choose Paste from the resulting menu (or just use CTRL-V) . This will take the info that's currently sitting on the clipboard (i.e. the web page text in this case) and attempt to put it into my word processing document.

I say "attempt to put the info on the clipboard into the word processor" because sometimes the info that's on your clipboard is not compatible with the program you're using. For example, if you try to paste a picture into notepad, that just isn't going to work.

For example, lets say you were working on a report in MS Word and you would like to quote some information you uncovered on the web. Rather than printing out the web page and re-typing the block of text you would like to quote, you can highlight the text on the webpage and copy it to the clipboard (highlight by holding down your left mouse button and dragging it over the section of text you would like to have. Copy it by right-clicking that section of text and selecting Copy from the menu that pops up).

Now, head back to MS Word and position the cursor where you would like to insert the text. Hit CRTL-V (or click the Edit menu, Paste ), and presto, the web page text you copied has now been pasted into your Word doc.

A filename extension is a suffix to the name of a computer file applied to indicate the encoding convention (file format) of its contents.

In some operating systems (for example Unix) it is optional, while in some others (such as DOS) it is a requirement. Some operating systems limit the length of the extension (such as DOS and OS/2, to three characters) while others (such as Unix) do not. Some operating systems (for example RISC OS) do not use filename extensions. Unix accepts the separator dot as a legal character but does not give it a special recognition on the OS level.

Last modified: Friday, January 18, 2008 

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(1) Refers to the condition of a disk in which files are divided into pieces scattered around the disk. Fragmentation occurs naturally when you use a disk frequently, creating, deleting, and modifying files. At some point, the operating system needs to store parts of a file in noncontiguous clusters. This is entirely invisible to users, but it can slow down the speed at which data is accessed because the disk drive must search through different parts of the disk to put together a single file.

In DOS 6.0 and later systems, you can defragment a disk with the DEFRAG command. You can also buy software utilities, called disk optimizers or defragmenters, that defragment a disk.

See "Learn How to Defrag Your Hard Drive" in the Did You Know...? section of Webopedia.

(2) Fragmentation can also refer to RAM that has small, unused holes scattered throughout it. This is called external fragmentation. With modern operating systems that use a paging scheme, a more common type of RAM fragmentation is internal fragmentation. This occurs when memory is allocated in frames and the frame size is larger than the amount of memory requested