The operating system is a basic set of programs that provides an interface with the user, managing the hardware of the computer, working with files, inputting and outputting data, and executing application programs. The user interacts with the CS through an external interface organized by the operating system. And the user should not worry about writing special programs for working with hardware. These functions are performed by the OS. Therefore, programs can run on any computer with different hardware, since I interact with the OS, not with the hardware.

The OS is designed to perform the following functions:

1. Distribution of aircraft resources.

2. Organization of multiprogram operation modes.

3. Management of tasks, devices, memory, processors.

4. Increasing the reliability and efficiency of the operation of the Armed Forces.

The operating system not only allows you to run application programs, but it is also a mechanism that distributes computer resources during the operation of these programs. The resources of the computer are distributed among the processes. The process is the basic concept of most operating systems, and is most often defined as a program in progress.

Multitasking the operating system is switching the processor from one process to another, and also tracks conflicts when accessing shared resources.

Among the main characteristics of operating systems include bit capacity, support for multiprocessing, multitasking, portability, support for multi-user mode.

The size of the operating system shows how much the internal bus of the CPU can support the operating system. The size of the operating system indicates which programs it will work with. All modern operating systems support a 32-bit application program interface. The bit depth of the application program interface code is directly related to the address space of the RAM.

The memory address space is the memory address space allocated between the individual operating system software modules and the data. The address space is also distributed between the video memory, BIOS memory, the protected mode information block, and so on.

The operating system can support two modes of operation of the central processor - real and protected. In the real mode of operation, typical for the MS DOS operating system, all programs and data are located in one area of ​​RAM.

The mode of sharing the address space, in which less priority programs can not get into the memory area in which higher priority programs are stored, and spoil them, is called protected.

32-bit operating systems support a protected mode that allows you to store programs and data separately, according to their importance in the system.

Most modern operating systems are well-structured modular systems that can be developed, expanded, and ported to new platforms. There are a number of universal approaches to the structuring of operating systems, among which one can distinguish monolithic and micronuclear architectures.

Most operating systems use a monolithic kernel that is linked as one program running in a privileged mode and using fast transitions from one procedure to another, not requiring switching from the preferred mode to the user mode and vice versa. This core is divided into main components and modules that implement additional functionality, for example, work with specific external devices and file systems. The transition from the user mode to the kernel mode is done through system calls - the kernel interface of the operating system.

An alternative is to build an operating system based on a microkernel that also operates in a privileged mode and performs only a minimum of hardware management functions. In this case, higher-level functions of the operating system are performed by specialized components (servers) operating in user mode. Management and data exchange is carried out through the transmission of messages, the delivery of which is one of the main functions of the microkernel.