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One can appreciate that an operating system acts as an interface between the hardware of a computer system and the user or program for aplication.

Operating system functions

   To serve as the interface between hardware and users, an operating system must be able perform the following functions: 36366ixc44vek7y.

1.Oferirea possibility of execution of application programs. In this regard, the operating system must have:

-a text editor

– an interpreter xe366i6344veek

-link editor

2.Alocated resources needed to execute programs, is achieved by identifying: the programs that are executed, the memory requirements, peripheral devices and data protection requirements.

3.Facilities for data compression, sorting, merging, cataloging and maintenance of libraries, utility programs available.

4.Planning the execution of works according to certain criteria, for efficient use of central processing unit.

5.Assisting communication programs through execution-user computing system, both at hardware and software level.

Operating system components

   Most operating systems to respond to the role of hardware interface – users are organized on two levels:

1.physical level, which is closer to the hardware of the computer system, interfering with the system through a interrupt.

2.logical level, which is closer to the user, interfering with it by means of commands, programming languages, tools, etc…

    According to these two levels, operating systems include two main categories of programs:

1. command and control programs, the role of coordination and control of all functions of operating systems, such as input-output processes,execution interruptions, hardware-user communication;

2. service programs (processing), which are performed under the supervision of command and control programs being used by programmers for application development of its programs.

Development of operating systems

   The first operating systems were made by batch processing programs. Communication operations that were to be achieved is through a command language that allowed interpretation of instructions to the system, and error handling statements. Such systems operating in the mono-programming.

    CPU (central processing unit) can execute only one instruction in a certain quantum of time and can not work only with data that are found internal memory, if peripheral input devices are slow in providing data to internal memory or programs,CPU must wait for transferring data / programs in the internal memory to begin execution of the program.

    If the computer system has a simple operating system, then processing is performed several serial programs,leading to an inefficient use of CPU.

Types of operating systems

     Basically, if there are two types of personal computer operating systems:

1. mono-tasking, which run one program at a time, making two basic functions:

                      –  loading and executing programs

                      – ensuring interference with peripheral devices.

2. multitasking operating system kernel which should provide additional type sharing between programs that are executed and resource allocation management system, the main components included:

                       – supervisor, to launch, stop or suspend allocations;

                       – scheduler, which adjusts the execution time for operations in progress;

                       – allocated to resource that highlights free or allocated resources;

                       – management module for inputs / outputs, ensuring dialogue with peripherals.

The main types of existing operating systems on PCs

             – MS-DOS (Microsoft Disk Operating System)                 

             – OS/2 (Operating System/2)

             – Apple DOS

             – UNIX

             – Windows 3.1

             – Windows NT (NT – New Technology)

             – Windows 95

             – Windows 98

             – Windows 2000

             – Windows Xp


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