Basics of Operating Systems

Definition:

Operating Systems are resource managers. The main resource is computer hardware in the form of processors, storage, input/output devices, communication devices, and data. Some of the operating system functions are: implementing the user interface, sharing hardware among users, allowing users to share data among themselves, preventing users from interfering with one another, scheduling resources among users, facilitating input/output, recovering from errors, accounting for resource usage, facilitating parallel operations, organizing data for secure and rapid access, and handling network communications.

How an Operating System works?

 

Operating systems control different computer processes, such as running a spreadsheet program or accessing information from the computer's memory. One important process is interpreting commands, enabling the user to communicate with the computer. Some command interpreters are text oriented, requiring commands to be typed in or to be selected via function keys on a keyboard. Other command interpreters use graphics and let the user communicate by pointing and clicking on an icon, an on-screen picture that represents a specific command. Beginners generally find graphically oriented interpreters easier to use, but many experienced computer users prefer text-oriented command interpreters.

Operating systems are either single-tasking or multitasking. The more primitive single-tasking operating systems can run only one process at a time. For instance, when the computer is printing a document, it cannot start another process or respond to new commands until the printing is completed.

All modern operating systems are multitasking and can run several processes simultaneously. In most computers, however, there is only one central processing unit (CPU; the computational and control unit of the computer), so a multitasking OS creates the illusion of several processes running simultaneously on the CPU. The most common mechanism used to create this illusion is time-slice multitasking, whereby each process is run individually for a fixed period of time. If the process is not completed within the allotted time, it is suspended and another process is run. This exchanging of processes is called context switching. The OS performs the “bookkeeping” that preserves a suspended process. It also has a mechanism, called a scheduler, that determines which process will be run next. The scheduler runs short processes quickly to minimize perceptible delay. The processes appear to run simultaneously because the user's sense of time is much slower than the processing speed of the computer.
 

 Software Program:
An Operating System is a software program or set of programs that mediate access between physical devices (such as a keyboard, mouse, monitor, disk drive or network connection) and application programs (such as a word processor, World-Wide Web browser or electronic mail client).

 Device Manager:
The operating system provides a set of APIs to the applications for accessing input/output (I/O) devices in a consistent and relatively simple manner regardless of the specifics of the underlying hardwar 

 Security:
Operating systems provide security by preventing unauthorized access to the computer's resources. Many operating systems also prevent users of a computer from accidentally or intentionally interfering with each other

 Slicer :
Modern operating systems provide the capability of running multiple application programs simultaneously, which is referred to as multiprogrammingThe operating system can share the CPU among the processes by using a technique known as time slicing

 Resource Allocator:
The operating system is responsible for sharing the memory among the currently running processes 

 Coordinator:
Manages all resources and settles conflicting requests for resources and also prevent errors and improper use of the computer

 Facilitator :
Provides facilities that everyone needs standard Libraries, Windowing systems which make application programming easier, faster, less error-prone

 Examples of OS:

UNIX , LINUX,Windows NT,Windows 95/98,Netware