OPERATING SYSTEMS

OPERATING SYSTEMS

A computer system can not process the data without being programmed. A program is a collection of instructions that the computer is required to solve a certain problem. The software component of a computer is a set of programs.  

                Computer software is structured as follows:
- Application programs
- Programs System
- Utilities
- operating system
- core
- interface
a) the application programs - are used to execute particular character activities specific to a user. (Ex: Turbo Pascal, Microsoft Word)
b) system software - are used to perform common activities of computing in general. They can be used on the same family of computers, regardless of the purpose for which the user uses the computer.
System programs consist of utility programs and operating system.

Utility programs are used to perform common activities of many types of users. The operating system is a component of the structure and represents all computer programs that manage computer system resources, ensure efficient use of these resources and offer more convenient user interface how to use the computer system. They are not part of the operating system as the computer can work without them. (Ex: zippers / unzip: Rar, Arj, WinRAR, WinZip, Ace; antivirus software: Norton Antivirus, AVX, Mkafee, F-Prot, Tbav, AVP, assistance programs operating systems: Norton Commander, Dos Navigator Windows Commander).
             
The operating system is a collection of programs used to manage and control the entire computer's resources activities. He liaises between user and computer, copy the programs executable file on disk in the internal memory, execute instructions in order of these programs and communicate results.
The operating system consists of two components: core and interface.
                The nucleus contains all the necessary programs for managing computer resources and for controlling the activity of equipment and software.
                OS interface defines how the user interacts with the operating system. It provides communication between the user and the computer follows: the user transmits commands via the keyboard or computer mouse and the computer user sends messages through the monitor.
                The most widely used operating systems are MS-DOS and Windows 95/98. Other operating systems are UNIX, NOVELL, WINDOWS 3.11., Windows NT, Windows 2000 OS / 2.
                        An operating system must fulfill the following functions:
- to control program execution (internal memory to load programs, to launch them in execution and terminates them);
- to plan, coordinate and control the execution of several programs by certain criteria (execution time, priorities, etc.);
- to allocate the resources needed to execute programs;
- to perform operations input / output;
- manage file system;
- to protect against users, and protection of applications programs;
- to detect and correct errors that occur in the manufacturing process;
-to notify special events that occur during execution and treat them appropriately;
- to provide the user interface to enable its access control program, intervention in the execution of programs and examination system status;

Because the operating system kernel contains the software required to manage computer resources, it must be permanently resident in memory. But internal memory is volatile, its contents when power is lost. Because of this, at the beginning of each session working with the computer must be loaded into internal memory the operating system kernel.
When the computer starts a program called preloaded in the ROM initializes peripherals, computer configuration and identify magnetic medium that is looking to have an operating system. If found, the program loaded in the internal memory called wheel carrier is found early and it launches the execution. This program in turn loaded into RAM internal memory the operating system kernel and it launches the execution. Programs operating system will load into RAM in turn various utility programs or software application will launch and execution.
MICROSOFT
Multiprogramming processor is shared between several programs are loaded into memory at the same time. From this point of view, there are two types of operating systems: monotasking and multitasking. Monotasking operating systems (which allow working in monoprogramare) can run one program at a time.  Multitasking operating systems (which allow working in multiprogramming) can run multiple programs simultaneously. These systems are advantageous because they allow optimal use of CPU.