Operating systems

OS allows to abstract from parts of sale of the hardware, providing to software developers minimum necessary feature set.

Concept of the operating system

Operating systems are a basis of the software of the computers (C) and their systems – the computing systems (CS). The idea that OS first of all the system providing a user-friendly interface to users corresponds to its consideration from top to down. Other look, from below up, gives an idea of OS as of some mechanism, distributing and managing all components and the VM and AF resources for the purpose of ensuring maximum efficiency of their functioning.

What reasons of change of OS in the company?

The solution to replace the operating system comes in a type of different circumstances.

First, when the new application version used for the solution of routine tasks requires functions of new OS. (For old OS) the developer is not interested in support of other versions of applications.

Secondly, the company wants to give to employees an opportunity for work with corporate resources, for example, from mobile devices, and restrictions in OS do not give such functionality. What, in turn, affects performance.

And, thirdly, the most important reason of transition to new versions of OS, is threats of information security and as a result risk of loss of information. This question is particularly acute in the companies working with personal data of users. According to the federal law on personal data (FZ-152) the operator should provide technical protection of the data entrusted to it. By the operating system it means that the operator is obliged to study the bulletin of security, to estimate risks and to set the security updates released by the developer, otherwise the operating system becomes vulnerable for the threats described in the bulletin.

Directory of Operating systems

• Operating systems - Product catalog and systems

Real-time Operating System (RTOS)

• [[* [[OSRV Real-time operating system|* OSRV Real-time operating system

Basic principles of creation of operating systems

• The principle of modularity - the isolation of components of OS in separate modules (functionally finished system elements) executed according to the accepted intermodular interfaces;
• The principle of a generiruyemost of OS - defines such method of initial representation of a kernel of OS and principal components of OS which allows to make their setup, proceeding from a specific configuration of the specific computer system and a circle of solvable tasks;
• The principle of functional redundancy - considers a possibility of carrying out the same work as different means;
• The principle of virtualization - presents structure of a system in the form of a certain set of schedulers of processes and distributors of resources and allows to use the uniform centralized scheme of resource allocation, organizing thereby operation of the virtual machine;
• The principle of independence of programs of external devices - contact of programs with specific devices is made not at the level of broadcast of the program, and in a planning period of its execution;
• The principle of compatibility - capability of OS to execute the programs written for other OS or for earlier versions of this operating system and also for other hardware platform;
• The principle of the opened and increased OS - allows not only to use possibilities of generation, but also to enter new modules into its structure;
• The principle of security at accomplishment of calculations - is desirable property for any multi-user system;

Architecture of the operating system

Основная статья: Architecture of the operating system

The multitasking and distribution of powers require a certain hierarchy of privileges of components of OS. As a part of OS distinguish three groups of components:

• the core containing the scheduler; the drivers of devices which are directly managing the equipment; network subsystem, file system;
• system libraries and
• cover with utilities.

The majority of programs as system (entering OS), and applied, are performed in an unprivileged ("user") operation mode of the processor and get access to the equipment (and, if necessary, to other nuclear resources and also resources of other programs) only by means of system calls. The core is performed in a kernel mode: in this sense say that OS (more precisely, its core) manages the equipment.

In determination of structure of OS the criterion of operational integrity (isolation) matters: a system should allow to use fully (including modification) the components. Therefore include in complete structure of OS also a set of work benches (from text editors to compilers, debuggers and binders). The majority of modern operating systems represents well structured building block systems capable to development, expansion and transfer of new platforms. One of options of structurization of OS - selection monolithic and micronuclear architecture.

Functions

Основная статья: Functions of the operating system

Basic functions (simplest OS):

• Loading of applications in RAM and their accomplishment;
• The standardized access to peripheral devices (input/output device);
• Management of RAM (distribution between processes, a virtual memory);
• Access control to data on non-volatile carriers (such as Hard drive, Compact disk, etc.), as a rule using the file system;
• User interface;
• Network transactions, support of a stack of protocols

Evolution of operating systems and main ideas

Основная статья: Evolution of operating systems

The predecessor of OS should be considered utility programs (loaders and monitors) and also libraries of often used subprogrammes which began to be developed with the advent of multipurpose computers of the 1st generation (the end of the 1940th years). Utility programs minimized physical manipulations of the operator with the equipment, and libraries allowed to avoid repeated programming of the same actions (implementation of input-output operations, calculation of mathematical functions, etc.).

History OS contains approximately half a century. It in many respects was defined and defined by development of element base and the computing equipment.

• First generation.

The 40th years. The first digital computers without OS. The organization of computation process decides the programmer from the control panel.

• The second generation.

The 50th years. Emergence of a prototype of OS - the monitor systems implementing batch processing system of tasks.

• Third generation.

1965-1980. Transition to integrated circuits. IBM/360. Practically all main concepts inherent in modern OS are implemented: time sharing and multitasking, separation of powers, real-time scale, file structures and file systems. Implementation of multiprogramming demanded entering of very important changes into the computer equipment: the exclusive and user modes, means of protecting of areas of memory, the developed system of interruptions.

• Fourth generation.

End of the 70th. The working option of a stack of protocols TCP/IP is created. In 1983 it was standardized. Independence of producers, the flexibility and efficiency proved by successful work the Internet made this stack of protocols the main stack for the majority of OS.

The 80th years. Emergence of personal computers. Rapid growth of local networks. Support of network functions became a necessary condition. Fundamental standards on communication technologies of local networks are accepted: Ethernet, Token Ring, FDDI. It allowed to provide compatibility of network OS at the bottom levels.

Beginning of the 90th. Practically all OS became network. There were specialized network OS (for example IOS working in routers)

Last decade. Special attention to corporate network OS of which are characteristic high degree of scalability, support of network work, the developed security protections, capability to work in the heterogeneous environment, existence of means of the centralized administration.

OS in the world market

Основная статья: Operating systems (world market)

From the 1990th the most widespread operating systems for personal computers and servers are:

• OS of family Microsoft Windows and Windows NT;
• OS of family Mac OS and Mac OS X;
• systems of the class UNIX, and Unixpodobnye (especially GNU/Linux).

OS for the corporate sector

Основная статья: OS for the corporate sector

Effective work of IT infrastructure of any modern company is impossible without competently selected server operating system.

Purpose of server operating system is a management of the applications servicing all users of corporate network and external users (DBMS, means of the analysis and management of networks, directory services, means of exchanging messages and group work, Web servers, mail servers, corporate firewalls, application servers, server parts of business applications).

The choice of server operating system and hardware platform for it first of all is defined by a circle of solvable tasks, and what requirements are imposed to its performance, stability and availability. The main players in the market of server operating systems are OS of the Windows and Unix families.

Operating systems of the Windows family

Server versions of the Windows operating system are applied quite widely today — thanks to convenience of administration and low total cost of ownership.

• Windows 2000
• Windows Server 2003
• Windows Server 2008

Operating systems of the UNIX family

UNIX is group of multitasking multi-user operating systems. At present there is a large number of variations of OS in this sphere - as commercial, and with the open code.

• Linux
• FreeBSD
• Solaris

The majority of the Russian servers work under control of these or those clones from Unix. According to the selective research conducted by the RuMetrika portal (data for 2006 on the Russian servers certainly Free BSD (53%), on the second place of Linux (32%) is in the lead, the number of servers on which Windows OS is installed was 9%, Solaris - only 5% meets less often.

"Unix", standardization of OS and POSIX

Основная статья: "Unix", standardization of OS and POSIX

Conceived and implemented in 1969 by Ken Thompson with the assistance of several colleagues (including Dennis Richie and Brian Kernighan), Unix OS ("Unix"; originally "UNICS" that beat the name "MULTICS") incorporated many lines of earlier OS, but had a number of the properties distinguishing it from most of predecessors:

• simple metaphorics (two key concepts: computation process and file);

• component architecture: the principle "one program — one function" plus powerful tools of binding of different programs for the solution of the arising tasks ("cover");

• minimization of a core (the code which is executed in the "real" ("exclusive") mode of the processor) and quantity of system calls;

• independence of hardware architecture and implementation in a machine-independent programming language (the Si programming language became "by-product" of development of "Unix");

• standardization of files.

Thanks to competition of implementations the architecture of Unix OS became the actual industry standard in the beginning, and then found the status and the standard legal — ISO/IEC 9945.

The OS following the standard or relying on it call "POSIX - compatible"

Standardization of OS guarantees a possibility of painless replacement of OS and/or the equipment at development of the computing system or network and cheap transfer of the application software (strict following to the standard assumes full compatibility of programs at the level of a source text; because of profiling of the standard and its development some changes nevertheless are necessary, but transfer of the program between POSIX - the compatible systems costs on orders cheaper, than between alternative) and also succession of experience of users.

Effective deployment of the Internet in the nineties became the most noticeable effect of existence of this standard.

"Post Unix" of architecture of OS

The collective which created Unix OS tried to repeat later the success, having generalized and having added the initial concept. Thus there were OS "Plan9" and "Inferno", not widely adopted, however.

Later on the basis of "Plan9" in Spain OS "Off++" and "Plan B", having experimental character were developed.

It is also possible to refer to attempts to create postyuniksovsky architecture development of the system of programming and operating environment "Oberon" in Swiss federal Institute of Technology (ETH Zurich) under the direction of prof. Nicklaus of Wirth.