Functions of OS operating systems. System software. Composition of system software. The concept of an operating system (OS). Purpose, main functions and types of OS

Operating systems occupy a special place among software of all types, being the core of the software.

An operating system is a set of programs that provide:

* resource management, i.e. coordinated operation of all computer hardware;
* process management, i.e. execution of programs, their interaction with computer devices and data;
* user interface, i.e. dialogue between the user and the computer, execution of certain simple commands - information processing operations.

This definition of an operating system already refers to its functions, so let’s look at these functions in more detail.

Operating systems are the most machine-dependent type of software, focused on specific computer models, since they directly control their devices or, as they say, provide an interface between the user and the computer hardware.

To the extent necessary to understand the functions of operating systems, computer hardware can be thought of as consisting of the following elements:

* a central processor having a specific architecture (register structure, set and form of command presentation, format of processed data, etc.) and characterized by performance, i.e. the number of simple operations performed per unit of time, as well as other qualities;
* RAM, characterized by capacity (volume) and speed of data exchange (primarily with the central processor);
* peripheral devices, among which are;
* input devices (keyboard, mouse, scanner, etc.);
* output devices (display, printer, plotter, etc.);
* external storage devices (drives for magnetic and optical disks, devices for working with tapes, etc.);
* multimedia devices.

All these hardware devices are collectively called computer resources.

Compared to RAM, external storage devices have virtually unlimited capacity. Thus, the capacity of the built-in storage device of personal computers - the hard drive - is usually 50-100 times greater than the volume of RAM. For other devices - floppy disk drives and optical disk drives - removable storage media are used, but the access time to information on external storage devices is much longer than information in RAM (thousands of times). Input and output devices also operate slower than the central processor.

During the existence of computers, operating systems have undergone significant evolution. Thus, the first operating systems were single-user and single-tasking. The efficiency of using computer resources in this case turned out to be low due to the downtime of all but one working computer peripheral device. For example, the central processor, output devices, and external storage devices were idle during data entry.

As capabilities, performance, and cost ratios of computer devices grew, the situation became intolerable, leading to the emergence of multitasking operating systems that remained single-user.

Such operating systems provide queuing of jobs for execution, parallel execution of jobs, and division of computer resources between running jobs. So, for example, one task can perform data input, another can be executed by the central processor, a third can output data, and a fourth can stand in a queue. The most important technical solution that led to such possibilities is the appearance of external devices with their own processors (controllers).

When multitasking:

* there are several user tasks in RAM;
* processor operating time is divided between programs located in RAM and ready to be serviced by the processor;
* in parallel with the operation of the processor, information is exchanged with various external devices.

The most advanced and complex multi-user multitasking operating systems that allow many tasks to be performed simultaneously by many users provide resource sharing computer in accordance with user priorities and data protection each user from unauthorized access. In this case, the operating system runs in time sharing, those. serves many users, each working from their own terminal.

The essence of the time sharing mode is as follows. Each program located in RAM and ready for execution is allocated for execution a fixed time interval (multiplexing interval), set in accordance with the user's priority. If the program is not completed to completion within this interval, its execution is forcibly interrupted and the program is moved to the end of the queue. The next program is retrieved from the beginning of the queue, executed during the corresponding multiplexing interval, then goes to the end of the queue, and so on. in accordance with the cyclic algorithm. If the multiplexing interval is small enough (~200 ms), and the average length of the queue of programs ready for execution is small (~10), then the next time slice is allocated to the program every 2 s. Under these conditions, none of the users feel any delays, since they are comparable to human reaction time.

One variation of time-sharing mode is background mode, where a program with a lower priority runs in the background of a program with a higher priority. Working in the background in real time is similar to the work of an executive secretary. The secretary deals with current affairs until the boss gives an urgent order. operating computer processor file

In addition to the considered modes of organizing the computing process, a scheme in which the computer controls some external process, processing data and information directly coming from the control object, is becoming increasingly widespread. Since the determining factor is the data actually coming from the control object, this mode is called real time, and its organization is entrusted to a specialized operating system.

Let's dwell on some concepts that are important for understanding the principles of operation of all operating systems (OS).

Concept process plays a key role and is introduced in relation to each individual user program. Managing processes (both as a whole and individually) is the most important function of the OS. When executing programs on a central processor, the following characteristic states should be distinguished (Fig. 1):

* generation - preparing conditions for execution by the processor;
* active state (or "Account") - direct execution by the processor;
* expectation - due to the busyness of any required resource;
* readiness - the program is not executed, but all resources necessary for program execution, except the central processor, are provided;
* ending - normal or abnormal termination of program execution, after which the processor and other resources are not provided to it.

Rice. 1.

The concept of “resource” in relation to computer technology should be understood as a functional element of a computing system that can be allocated to a process for a certain period of time. Along with physical resources - real computer devices - using modern operating systems, virtual (imaginary) resources, which are models of physical ones, can be created and used. In terms of importance, virtual resources are one of the most important concepts in building modern operating systems. A virtual resource is a model of a physical resource created using another physical resource. For example, a typical representative of a virtual resource is RAM. Computers, as a rule, have limited RAM (physical) memory. Functionally, its volume can be increased by partially writing the contents of RAM to a magnetic disk. If this process is organized in such a way that the user perceives all extended memory as RAM, then such “RAM” memory is called virtual.

The most complete manifestation of the concept of virtuality is the concept of a virtual machine, which is the starting point for programming in high-level languages, for example, Pascal. A virtual machine is an idealized model of a real machine, isolating the user from the hardware features of a particular computer, reproducing the architecture of a real machine, but with improved characteristics:

* infinite memory with randomly selected methods of accessing its data;
* one (or several) processes described in a user-friendly programming language;
* an arbitrary number of external devices of arbitrary capacity and access.

Concept interrupts program execution is basic when building any operating system. Of the variety of causes of interruptions, it is necessary to distinguish two types: the first and second kind. System causes of interruptions of the first kind arise when a process in an active state has a need to either obtain or refuse a certain resource, or to perform some action on the resource. This group also includes the so-called internal interrupts associated with the operation of the processor (for example, arithmetic overflow or disappearance of order in floating point operations). System reasons for interruptions of the second type are due to the need for synchronization between parallel processes.

When processing each interrupt, the following sequence of actions must be performed:

* perception of interruption request;
* storing the state of an interrupted process, determined by the value of the program counter and other processor registers;
* transfer of control to the interrupting program, for which the address corresponding to this type of interrupt is entered into the program counter;
* interrupt handling;
* restoration of an interrupted process.

In most computers, the first three stages are implemented by hardware, and the rest by a block of interrupt handling programs of the operating system. Currently, many types of different operating systems are used for computers of various types, but there are general principles in their structure. As part of many operating systems, there is a certain part that is the basis of the entire system and is called the kernel. The kernel includes the most frequently used modules, such as the interrupt system control module, and means for distributing such basic resources as RAM and processor. When the OS boots, the programs that are part of the kernel are placed in RAM, where they are permanently located and used during the operation of the computer. Such programs are called resident programs. Resident programs also include driver programs that control the operation of peripheral devices.

An important part of the OS is command processor- a program responsible for interpreting and executing simple commands given by the user and its interaction with the OS kernel. In addition, the operating system should include a rich set of utilities- usually small programs that serve various computer devices (for example, a utility for formatting magnetic disks, a utility for recovering thoughtlessly deleted files, etc.).

Main functions:

· Performing, at the request of programs, those fairly elementary (low-level) actions that are common to most programs and are often found in almost all programs (data input and output, starting and stopping other programs, allocating and freeing additional memory, etc.).
· Loading programs into RAM and executing them.
· Standardized access to peripheral devices (input/output devices).
· RAM management (distribution between processes, organization of virtual memory).
· Controlling access to data on non-volatile media (such as a hard drive, optical disks, etc.), organized in a particular file system.
· Providing a user interface.
· Network operations, support for network protocol stack.

Additional functions:

· Parallel or pseudo-parallel execution of tasks (multitasking).
· Efficient distribution of computing system resources between processes.
· Differentiation of access of various processes to resources.
· The organization of reliable computing (the inability of one computing process to intentionally or mistakenly influence calculations in another process) is based on the delimitation of access to resources.
· Interaction between processes: data exchange, mutual synchronization.
· Protecting the system itself, as well as user data and programs, from actions of users (malicious or unknowing) or applications.
· Multi-user mode of operation and differentiation of access rights (see authentication, authorization).

An operating system is a set of software that provides control of computer hardware and application programs, as well as their interaction with each other and the user. In most computing systems, operating systems are the main part of the system software.

The operating system acts as a link between the computer hardware, on the one hand, and the programs being executed, as well as the user, on the other hand. The operating system is usually stored in the computer's external memory - on disk. When you turn on the computer, it is read from disk memory and placed in RAM. This process is called loading the operating system.

The operating system can be called a software extension of the computer's control device. It hides complex unnecessary details of interaction with the equipment from the user, forming a layer between them. As a result of this, people are freed from the very labor-intensive work of organizing interaction with computer equipment.

The operating system, on the one hand, acts as an interface between the computer hardware and the user with his tasks, on the other hand, it is designed for the efficient use of computer system resources and the organization of reliable computing.

Main functions of operating systems:

Standardized access to peripheral devices (input/output devices).

RAM management (distribution between processes, virtual memory).

Controlling access to data on non-volatile media (such as a hard drive, CD, etc.) organized in a particular file system.

User interface.

Network operations, protocol stack support.

Parallel or pseudo-parallel execution of tasks (multitasking).

Interaction between processes: data exchange, mutual synchronization.

Protecting the system itself, as well as user data and programs, from actions of users (malicious or unknowing) or applications.

Differentiation of access rights and multi-user mode of operation (authentication, authorization).

Different computer models use operating systems with different architectures and capabilities. They require different resources to operate. They provide varying degrees of service for programming and working with ready-made programs. Depending on the number of simultaneously processed tasks and the number of users that the OS can serve, there are four main classes of operating systems:

Single-user, single-tasking, which supports one keyboard and can only work on one (at the moment) task;

Single-user, single-task with background printing, which allow, in addition to the main task, to launch one additional task, usually focused on printing information. This speeds up work when printing large volumes of information;

Single-user multitasking, which provides one user with parallel processing of several tasks. For example, you can connect several printers to one computer, each of which will work for its “own” task;

Multi-user multitasking, allowing multiple tasks to be run by multiple users on one computer. These operating systems are very complex and require significant machine resources.

The most common operating systems are:

Mac OS is the operating system of Apple Corporation.

OS/2 is an operating system from IBM.

Windows is the operating system of Microsoft Corporation.

Linux is the general name for Unix-like operating systems based on the kernel of the same name and libraries and system programs compiled for it, developed within the GNU project.

The operating system is an intermediary between the computer and the user, ensuring their interaction and being responsible for executing programs. The most famous representatives: Linux, Microsoft, Mac OS and so on. In this article we will look at the composition and functions. We will talk about general parameters without reference to a specific OS.

What does the operating system consist of?

Before we talk about what functions of operating systems there are, we will look at what it consists of.

A software module that manages a file system.
Drivers for devices. They ensure the correct operation of each hardware element of the computer, as well as information exchange with other devices.
A processor that responds to user commands.
Service programs. With their help, it is possible to work on computer networks with disks and files.
Modules that provide a graphical shell for the user.
A help system that helps you find the answer to any question regarding the operating system and working with it.

The functions of operating systems may vary depending on the type of the latter. There are quite a lot of classifications. Let's give the main ones.

1. Based on the number of concurrent users, OSes are divided into: single-user (old versions, for example, MS-DOS, Windows 3.x, early versions of OS/2) and multi-user (for example, UNIX, Windows NT).

2. By the number of simultaneously performed tasks: single-tasking (for example, MSX, MS-DOS) and multi-tasking Windows 95, UNIX).

What does the operating system do?

Let us now consider the main functions of the operating system:

execution of user commands upon request (launching and closing programs, input and output of information, freeing up additional memory, and so on);
access to (printer, mouse, keyboard, etc.);
loading software into RAM and executing it;
exercise by memory;
saving data about errors and failures in the system;
providing a user interface;
accessing and managing other storage media.

That is, all actions performed by a person using input tools are performed by a computer using the OS. It allows you to provide convenient There are also additional functions of operating systems:

multitasking;
differentiation of access rights;
efficient distribution of resources between processes;
protection of the system and user data;
interaction between processors and their synchronization.

The system shell, to which we are so accustomed, provides us with the opportunity to comfortably use computer resources. The purpose and functions of operating systems are ease of communication with the machine, structuring and automation of processes. Over the years, developers and creators of shells for personal computers have made life easier for us, ordinary users and programmers, by introducing new features and reducing manual work. There is even an opinion that in the near future machines will largely replace humans.

The main component of the basic system software is operating system (OS), which is installed on the computer's hard drive and performs a huge amount of work that is not visible to the user. If we roughly take computer software as an iceberg, then the operating system can be compared to the underwater part of the iceberg.

operating system – This is a set of interrelated programs designed to provide the user, as well as system and application programs, with a convenient way to communicate with the computer through the keyboard and mouse.

OS are classified according to the following criteria.

Distinguish single-program and multi-program modes OS operation. Multiprogram – a mode in which several programs are executed on a single-processor system.

According to the organization of work in interactive mode, there are: single-user (single-terminal) and multi-user (multi-terminal) ) OS.

Class is highlighted real time OS, which differ in the execution of incoming commands at specified time intervals that cannot be exceeded.

The OS consists of modules. The file containing one of the OS modules is called system file. System files are located in the root directory of the hard drive. When you turn on the computer, the OS is read from the hard drive into RAM (loaded), as well as the OS is configured and launched.

OS structure contains the following components:

Core – These are the most commonly used OS modules, for example:

interrupt system control module;

means of RAM distribution;

means of allocating processor resources,

Resident programs – these are programs that are part of the kernel, for example, driver programs that control external devices; When the computer is operating, resident programs are constantly located in RAM,

Command processor – a program responsible for the interpretation and execution of simple commands given by the user, as well as for the interaction of these commands with the OS kernel,

File management system – a program for organizing convenient access to files. Each OS has its own file system.

Basic functions OS

receiving user commands and processing them;

receiving and executing requests to start and stop programs;

transfer of control to the loaded program;

ensuring the operation of the file management system;

providing multiprogramming mode, i.e. running two or more programs on one processor;

providing I/O operation;

memory allocation;

ensuring data safety and others.

3. Types of operating systems

Disk operating systems

The first computers did not have an operating system; control was carried out on the basis of simple programming languages, which were contained in ROM and made it possible to load programs and control the program from the keyboard.

In the early 80s, with the advent of magnetic disks, the first program was written in which specific track and sector numbers were assigned to each file name. This is how it appeared disk operating system – DOS . Next, the disk system was tasked with solving other tasks, for example, recording, copying and deleting files, eliminating duplicate names, etc. Due to the need to structure the growing volume of data, file directories appeared, from which a File structure , which was served by the operating system.

Microsoft (USA) from 1981 to 1995, gradually increasing complexity, released several versions of the system from MS - DOS 1.0 before MS - DOS 6.22

Disadvantages of disk operating systems:

the first operating systems were built on a text-character interface (a set of commands from the keyboard);

learning the latest versions of MS-DOS and solving computer problems required a lot of time.

Text shell programs

A shell program is an add-on to the operating system. , which simplifies work on the computer and runs under the operating system. Simplification consists of selecting commands or files from a list instead of typing from the keyboard.

The most famous shell program is Norton Commander , which clearly shows the entire file structure, allows you not to remember commands, but to work with them through the menu bar. Despite the emergence of more advanced programs, Norton Commander is still used on many computers.

Graphic shells

A text-based shell program like Norton Commander has been replaced by graphical operating system shell . Microsoft first created a graphical shell Windows 1.0 , then its versions appeared under the numbers 2.0; 3.0; 3.1; 3.11.

The Windows shell, which was called the environment, ran under MS-DOS and was not an independent operating system.

The Windows environment initially had the following features:

multitasking;

unified software interface;

unified user interface;

graphical interface;

unified hardware-software interface.

Graphics operating systems

The spread of graphical principles of program design to the entire operating system as a whole led to the creation graphical operating system. Microsoft is recognized as a leader in the development of graphic systems, which since the early 90s has created a number of operating systems, among which the most famous versions can be distinguished:

Windows NT – the first graphical operating system;

Windows 95 – the most popular version of the 90s;

Windows 98 – modified 95th version;

Windows 2000 – a system focused on corporate clients;

Windows XP – the most popular version for desktop computers since 2002;

Windows 7 – a popular system launched on the market in 2009;

Windows 8 – the version, which has been implemented since 2012, includes the ability to work with touch screens and has a tiled interface.

All versions of Microsoft operating systems are classified as licensed and are sold on the software market at commercial prices.

2.The concept of a file system.

3. Manage installation, execution and removal of applications

4. Interoperability with hardware

5. Computer maintenance

6. Other functions of operating systems

1. PURPOSE AND BASIC FUNCTIONS OF OPERATING SYSTEMS

operating system represents a complex of system and service software. On the one hand, it relies on the basic computer software included in its BIOS system (basic input/output system), on the other hand, it itself is the support for higher-level software - application and most service applications.

Operating system applications are usually called programs designed to work under the control of this system.

The operating system is designed to control the execution of user programs, planning and managing computer computing resources.

Operating systems for personal computers are divided into:

· single- and multi-tasking;

· single and multi-user;

· non-portable and transferable to other types of computers;

· non-network and network, providing work in a local computer network.

The main function of all operating systems is mediation. It consists of providing several types of interface:

· interface between the user and the computer hardware (user interface);

· interface between software and hardware (hardware-software interface);

· interface between different types of software (software interface).

Even for one hardware platform, such as the IBM PC, there are several operating systems. The differences between them are considered in two categories: internal and external. Internal differences are characterized by methods of implementing basic functions. External differences are determined by the availability and accessibility of applications of a given system necessary to meet the technical requirements for a specific workplace.

1.1.Providing a user interface

1.1.1.Modes of working with a computer

All operating systems are capable of providing both batch and interactive user interaction.

IN batch mode, the operating system automatically executes the specified sequence of commands.

The essence dialogue mode is that the operating system is waiting for a user command and, having received it, begins execution, and having executed it, returns a response and waits for the next command.

The interactive mode of operation is based on the use of processor interrupts and BIOS interrupts. Based on these hardware interrupts, the operating system creates its own set of system interrupts. The ability of the operating system to interrupt current work and respond to events caused by the user using control devices is perceived by us as an interactive mode of operation.

1.1.2.Types of user interfaces

Based on the implementation of the user interface, a distinction is made between non-graphical and graphical operating systems.

Non-graphical operating systems implement a command line interface.

Graphical operating systems implement a more complex type of interface, in which a mouse or an adequate positioning device can be used as a control in addition to the keyboard. Working with a graphical operating system is based on the interaction of active and passive on-screen controls. The active control element is the mouse pointer - a graphic object whose movement on the screen is synchronized with the movement of the mouse. Graphical application controls act as passive controls

The nature of the interaction between active and passive controls is chosen by the user.

1.2. Ensuring automatic start

All operating systems provide their automatic startup. For disk operating systems, a program code record is created in a special (system) area of the disk. This code is accessed by programs located in the basic input/output system (BIOS). When completing their work, they give a command to load and execute the contents of the system area of the disk.

Non-disk operating systems are typical for specialized computing systems, in particular for computerized automatic control devices. The mathematical software contained in the ROM chips of such computers can be conditionally considered as an analogue of the operating system. Its automatic launch is carried out in hardware. When power is applied, the processor accesses a fixed physical ROM address (it can be changed in hardware using logic chips), from which the recording of the operating system initialization program begins.

2.THE CONCEPT OF A FILE SYSTEM.

2.1. File system organization

All modern disk operating systems provide the creation of a file system designed to store data on disks and provide access to them. The principle of organizing the file system is tabular. The surface of a hard disk is considered as a three-dimensional matrix, the dimensions of which are the surface, cylinder and sector numbers.

A cylinder is understood as a set of all tracks belonging to different surfaces and located at an equal distance from the axis of rotation. Data about where on the disk a particular file is recorded is stored in the system area of the disk in special file allocation tables (FAT tables). Since violation of the FAT table makes it impossible to use the data recorded on the disk, it is subject to special reliability requirements, and it exists in two copies, the identity of which is regularly monitored by the operating system.

The smallest physical unit of data storage is a sector. The sector size is 512 bytes. Since the size of the FAT table is limited, for disks larger than 32 MB, it is not possible to provide addressing to each individual sector. In this regard, groups of sectors are conditionally combined into clusters. A cluster is the smallest unit of data addressing. The cluster size, unlike the sector size, is not fixed and depends on the disk capacity.

MS-DOS, OS/2, Windows 95, and Windows NT operating systems implement 16-bit fields in file allocation tables. This file system is called FAT 16. It allows you to place no more than 2 16 records about the location of data storage units in FAT tables and, accordingly, for disks with a capacity of 1 to 2 GB, the cluster length is 32 KB (64 sectors). This is not a completely rational use of work space, since any file (even a very small one) completely occupies the entire cluster, which corresponds to only one address entry in the file allocation table. Even if the file is large enough and is located in several clusters, a certain remainder is still formed at the end of it, wasting the entire cluster.

For modern hard drives, the losses associated with file system inefficiencies are significant and can range from 25% to 40% of the total disk capacity, depending on the average size of the files stored. The FAT 16 file system cannot work at all with disks larger than 2 GB.

2.2. File structure maintenance

Despite the fact that data on the location of files is stored in a tabular structure, it is presented to the user in the form of a hierarchical structure - this is more convenient for people, and the operating system takes care of all the necessary transformations. The file structure maintenance function includes the following operations that occur under the control of the operating system:

§ creating files and assigning names to them;

§ creating directories (folders) and assigning names to them;

§ renaming files and directories (folders);

§ copying and moving files between computer drives and between directories (folders) of one drive;

§ deleting files and directories (folders);

§ navigation through the file structure in order to access a given file, directory (folder);

§ file attributes management.

2.3. Creating and naming files

A file is a named sequence of bytes of arbitrary length. Since this definition implies that a file can have zero length, actually creating a file consists of giving it a name and registering it in the file system - this is one of the functions of the operating system.

According to the methods of naming files, a distinction is made between “short” and “long” names. According to MS-DOS 8.3 convention, a file name consists of two parts: the name itself and the name extension. The file name is allocated 8 characters, and its extension - 3 characters. The name is separated from the extension by a dot. Both the name and the extension can only include alphanumeric characters of the Latin alphabet.

The 8.3 convention is not a standard, and therefore, in some cases, deviations from the correct form of notation are allowed by both the operating system and its applications (for example, in most cases the system does not “object” to the use of some special characters, and some versions of MS-DOS even allow use of Russian and other alphabets in file names). Today, file names written according to the 8.3 convention are considered "short".

The main disadvantage of “short” names is their low content. With the advent of the Windows 95 operating system, the concept of a “long” name was introduced. This name can contain up to 256 characters. A “long” name can contain any characters except nine special characters: \ / : * ? "< >|.Spaces and multiple periods are allowed in the name. The name extension includes all characters after the last dot.

Along with the “long” name, the Windows 95,98,2000 operating systems also create a short file name - it is necessary to be able to work with this file on workstations with outdated operating systems.

The use of “long” file names in Windows operating systems has a number of features.

1. If the “long” file name includes spaces, then in service operations it must be enclosed in quotes. It is recommended not to use spaces, but to replace them with underscores.

2. It is not advisable to store files with long names in the root folder of the disk - unlike other folders, the number of storage units is limited in it, and the longer the names, the fewer files can be placed in the root folder.

3. In addition to the limit on the length of the file name (256 characters), there is a much more stringent limit on the length of the full file name (this includes the path to the file, starting from the top of the hierarchical structure). The full name cannot be longer than 260 characters.

4. It is allowed to use characters from any alphabets, including Russian.

5. Uppercase and lowercase letters are not distinguished by the operating system. However, characters of different registers are correctly displayed by the operating system, and if you need to use capital letters for clarity, this can be done.

6. In modern operating systems, any file name extension can carry information for the operating system. Windows systems have facilities for registering the properties of file types by their name extension, so in many cases the choice of file name extension is not a private matter for the user. Applications of these systems offer to select only the main part of the name and specify the file type, and the corresponding name extension is assigned automatically.

2.4. Creating directories (folders)

Directories (folders) are important elements of the hierarchical structure, necessary to provide convenient access to files if there are too many files on the media. Files are combined into directories according to any common characteristic specified by their creator (by type, by affiliation, by purpose, by time of creation, etc.). Directories at lower levels are nested within directories at higher levels and are nested for them. The top level of nesting of the hierarchical structure is the root directory of the disk.

We know that in hierarchical data structures, the address of an object is given by a route (access path) leading from the top of the structure to the object. When writing a file access path through a system of subdirectories, all intermediate directories are separated by a specific symbol. Many operating systems use "\" as this character, for example:

2.4.1.Windows Features

Before the advent of the Windows 95 operating system, the term directory introduced above was used to describe a hierarchical file structure. With the advent of this system, a new term was introduced - folder. With regard to maintaining the file structure of the storage medium, these terms are equivalent: each file directory on the disk corresponds to an operating system folder of the same name. The main difference between the concepts of folder and directory is manifested not in the organization of file storage, but in the organization of storage of objects of a different nature.

2.5.Copying and moving files.

In non-graphical operating systems, file copying and moving operations are performed by entering a direct command in the command line field.

In graphical operating systems, there are techniques for working with a positioning device that allow you to execute these commands using visual methods.

2.6.Navigation through the file structure

Navigating the file structure is one of the most used functions of the operating system. The convenience of this operation is often perceived as the convenience of working with the operating system. In operating systems that have a command line interface, navigation is accomplished by entering commands to move from disk to disk or from directory to directory. Due to the extreme inconvenience of such navigation, special utility programs called file shells have found widespread use.

Like operating systems, file shells can be non-graphical or graphical. The most famous non-graphical file shell for MS-DOS is the file manager. Norton Commander, and the role of a graphical file shell for MS-DOS at one time was played by the Windows 1.0 and Windows 2.0 programs, which gradually developed into the concept of an operating environment (in versions of Windows 3.x) and then into an independent operating system (Windows 95/98).

3. MANAGEMENT OF INSTALLATION, EXECUTION AND REMOVAL OF APPLICATIONS

3.1.The concept of multitasking

Working with applications is the most important part of the operating system. From the point of view of application execution management, a distinction is made between single-tasking and multi-tasking operating systems.

Single-tasking operating systems (such as MS-DOS) dedicate all computing system resources to a single executing application and do not allow another application to run in parallel (full multitasking) or to pause the application and start another application (preemptive multitasking). At the same time, in parallel with single-tasking operating systems, it is possible to operate special programs called resident ones. Such programs do not rely on the operating system, but work directly with the processor using its interrupt system.

Most modern graphical operating systems are multitasking. They manage the distribution of computing system resources between tasks and provide:

§ possibility of simultaneous or alternate operation of several applications;

§ the ability to exchange data between applications;

§ the ability to share software, hardware, network and other resources of a computer system with several applications.

3.2.Reliability issues

The reliability of the entire computing system largely depends on how the operating system manages the operation of applications. The operating system must provide the ability to interrupt applications at the user's request and remove a failed task without affecting the operation of other applications. At the same time, the requirement for the reliability of the operating system may conflict with the requirement for its universality.

For example, the most universal operating systems Windows 95,98,2000 may experience system-wide failures due to working with applications that do not strictly adhere to the operating system specifications. The operating systems Windows NT, OS/2 and XP have increased stability and do not fail when applications fail, but they have less versatility, and, accordingly, the fleet of available applications for them is limited.

Therefore, it is a generally accepted practice that a program is developed and debugged on the Windows NT, XP operating system, and its final assembly and compilation is performed on Windows 95/98, 2000.

3.3.Installing applications

For applications to work properly on your computer, they must go through an operation called installation. Thus, a distribution kit (installation package) of software, as a rule, is not a finished software product, but a semi-finished product, from which a full-fledged working application is formed during installation on a computer. In this case, the application is linked to the existing hardware and software environment and configured to work in this environment.

Legacy operating systems (such as MS-DOS) do not have the ability to manage application installations.

Modern graphical operating systems take control of application installation. They manage the distribution of computer system resources between applications, provide installed applications with access to computer system device drivers, form shared resources that can be used by different applications, and register installed applications and resources allocated to them.

3.4.Deleting applications

The process of uninstalling applications, like the installation process, has its own characteristics and can occur under the control of the computer system. In operating systems where each application is self-sufficient with its own resources (for example, in MS-DOS), its removal does not require special intervention from the operating system. To do this, simply delete the directory in which the application is located, along with all its contents.

In operating systems that implement the principle of resource sharing (for example, Windows 95/98), the process of uninstalling applications has its own peculiarities. Uninstalling one application should not remove resources that other applications rely on, even if those resources were once installed with the application being removed. In this regard, the removal of applications occurs under the strict control of the operating system.

4. ENSURING INTERACTION WITH HARDWARE

Computer hardware is extremely diverse. No software developer is able to provide all the options for how they can interact with their program.

The flexibility of hardware and software configurations of computing systems is maintained due to the fact that each equipment developer attaches special software management tools to it - drivers. Drivers have entry points for interacting with application programs, and dispatching application program calls to device drivers is one of the functions of the operating system. Strictly speaking, when releasing a device, its developer attaches to it several drivers designed for major operating systems, such as: Windows 95/98, Windows NT, MS-DOS, etc.

In MS-DOS operating systems, device drivers are loaded as resident programs that work directly with the processor and other devices on the motherboard. Loading device drivers can be manual or automatic, where commands to load and configure drivers are included in files that are automatically read when the computer boots.

In operating systems such as Windows 95/98 and Windows NT, the operating system takes care of all the functions of installing device drivers and transferring control from applications to them. In many cases, the operating system does not even need drivers obtained from the device developer, but uses drivers from its own database.

Each connected device can use up to three hardware resources of motherboard devices: external processor port addresses, processor interrupts, and direct memory access channels. If the device is connected to the motherboard via the PCI bus, then it is technically possible to organize feedback between it and the motherboard. This allows the operating system to analyze the requirements of devices to allocate resources to them and respond flexibly to them, eliminating the seizure of the same resources by different devices. This principle of dynamic resource allocation by the operating system is called plug-and-play, and devices that satisfy this principle are called self-installing.

If the device is connected to a legacy ISA bus and is not a patcher, then the operating system cannot dynamically allocate resources to it, but, nevertheless, when allocating resources to a patcher device, it takes into account the resources captured by it.

5. COMPUTER MAINTENANCE

Providing basic computer maintenance tools is one of the functions of the operating system; it is solved externally - by including priority service applications in the basic composition of the operating system.

5.1. Disk checking tools

The reliability of disks (especially a hard drive) determines not only the reliability of the computer as a whole, but also the security of storing data, the value of which can far exceed the cost of the computer itself. Therefore, the availability of tools for checking disks is a mandatory requirement for any operating system.

Verification tools are usually considered in two categories: logical verification tools, that is, checking the integrity of the file structure, and physical surface diagnostic tools. Logical errors, as a rule, are eliminated using the operating system itself, and physical surface defects are only localized.

File structure logical errors have two characteristic manifestations: orphan clusters or shared clusters. Lost clusters are formed as a result of an incorrect (or abnormal) shutdown of the computer. In addition, in Windows operating systems, you also cannot turn off the computer unless you perform a special procedure to shut down the operating system.

The error, which appears as shared clusters, is characterized by the fact that, according to FAT tables, two or more files claim to have their data in the same location on the disk. During normal operation, this situation cannot exist, and this indicates an error in the .FAT tables. The reason for the appearance of common clusters may be spontaneous changes in data in FAT tables or incorrect restoration of previously deleted data using non-system means.

5.2.Means for “compressing” disks

Some operating systems provide utilities for software "compression" of disks by writing data to the disk in a compressed form using a special driver (resident for MS-DOS or running in the background for Windows).

5.3.Virtual memory management tools

Early operating systems limited the ability to use applications based on the amount of RAM they needed to run.

Modern operating systems not only provide direct access to the entire field of RAM installed in the computer, but also allow it to be expanded by creating so-called virtual memory on the hard drive. Virtual memory is implemented in the form of a so-called page file. If there is insufficient RAM to run the application, part of it is temporarily emptied and the image is saved on the hard drive. During application operation, multiple exchanges occur between the main installed RAM and the paging file.

5.4.Disk caching tools

Since the interaction of the processor with computer disks occurs much slower than exchange operations with RAM, the operating system takes special measures to save part of the data read from the disk in RAM. If, during operation, the processor again needs to access previously read data or program code, it can find them in a special area of RAM called the disk cache. In modern operating systems, this function is included in the system kernel, and it works automatically, without user intervention, although a certain ability to customize the cache size is retained.

5.5. Data backup tools

The value of data stored on a computer is usually measured by the total costs that the owner may incur in the event of its loss. An important means of protecting data is regular backups to external media. Due to the special importance of this task, operating systems usually contain basic tools for performing