Operating system: purpose and classification of operating systems. General characteristics and basic mechanisms of the Windows operating system

Operating systems are classified by:

number of concurrent users: single-user, multi-user; the number of processes simultaneously running under the control of the system;

number of tasks to be solved: single-task, multi-task; number of supported processors: single-processor, multi-processor;

OS code bits: 8-bit, 16-bit, 32-bit, 64-bit; interface type: command (text) and object-oriented (graphical); type of user access to the computer: batch processing, time sharing, real time; type of resource use: network, local.

In accordance with the first sign of classification, multi-user operating systems, unlike single-user operating systems, support simultaneous work on the computer of several users at different terminals. The second sign involves dividing the OS into multi-tasking and single-tasking. The concept of multitasking means supporting the parallel execution of several programs existing within the same computer system at one point in time. Single-tasking operating systems support the execution mode of only one program at a time. In accordance with the third feature, multiprocessor operating systems, unlike uniprocessor operating systems, support the mode of distributing the resources of several processors to solve a particular task. The fourth sign divides operating systems into 8-, 16-, 32- and 64-bit. This implies that the bit capacity of the operating system cannot exceed the bit capacity of the processor. In accordance with the fifth characteristic, operating systems are divided into object-oriented (usually with graphical interface) and command (with a text interface). According to the sixth characteristic, operating systems are divided into systems:

batch processing

In accordance with the seventh classification criterion, operating systems are divided into network and local. Network operating systems are designed to manage the resources of computers connected to a network for the purpose of sharing data, and provide powerful means of restricting access to data to ensure their integrity and safety, as well as many service capabilities for using network resources. The following families of operating systems are currently common: DOS; OS/2; UNIX; Windows; Real time OS. OS of the DOS family The first representative of this family is MS-DOS system(Microsoft Disk Operating System- disk operating system from Microsoft) was released in 1981 in connection with the advent of the IBM PC. Operating systems of the DOS family are single-tasking and have the following characteristics and features:

random access memory

A significant disadvantage of operating systems of the DOS family is the lack of protection against unauthorized access to PC and OS resources. Currently, MS-DOS 6.22 is widely used. OS/2 family OS OS/2 was developed by IBM in 1987 in connection with the creation of the new PS/2 family of PCs. OS/2 (Operating System/2) is a second generation multitasking operating system. It is a 32-bit graphical multitasking operating system for IBM PC-compatible computers that allows you to organize parallel work several application programs, while protecting one program from another and the operating system from programs running in it. OS/2 has a convenient graphical user interface and compatible with file system DOS, which makes it possible to use data in both DOS and OS/2 without any conversion.

Properties of operating systems.

Any operating system is a work environment, in which the user can perform various functions, naturally within the permissible limits. It is not possible to determine whether a particular program can be executed by a particular operating system until the program is launched. There are programs that will not be able to perform any functions on the computer without some computer component. For example, there is no need to install a program on your computer to download images from the clipboard from a scanner if you do not have the scanner itself.

Modern operating systems have a graphical interface; the fashion for it began in the early 80s with the release of the first version of the MacOS operating system for ApplePC computers.

What is a graphical interface? The exact definition of a graphical interface is as follows: Graphical User Interface - Graphical User Interface, or GUI. If you try to translate the word “interface” into Russian, you will get something like “interface” or “interface”. In general, the graphical interface is a separate topic for discussion. Everything that the user sees when working on the computer graphical environment- this is the graphical interface. The elements of the GI are the desktop, shortcuts on the desktop, buttons, menus, various links, etc. What happened before the graphical interface appeared? It was dark, in the literal sense of the word. Before Windows came into existence computer world There were very few operating systems. These are MacOS, Unix, DOS. The graphical interface made it possible to simplify working with the computer as much as possible, since it became possible to work with the mouse.

The mouse is an integral part of controlling the graphical interface, because controlling it without a mouse, especially in all modern operating systems, is very difficult, but far from impossible. For every firefighter, there are keyboard shortcuts that were invented back in the days of DOS. And they were invented so that some functions could be performed without entering commands from the keyboard. In DOS itself, keyboard commands did not work; they worked in programs that were launched from it.

DOS was the most common operating system. DOS did not have a graphical interface and still does not have one. Working in DOS is working in text mode. The user enters commands from the keyboard, presses ENTER and gets the result, no matter what, negative or positive. The user specified each action manually. This was the period from 1968 to 1986, until the first attempts to create a normal graphical interface using a mouse began to appear in the computer world.

Unix resembled DOS, but initially it was generally a toy, and only then an operating system. A mandatory control element of the graphical interface is the mouse manipulator.

A common feature of most modern operating systems is multitasking. What it is? Multitasking is the ability of the operating system to use the processor to execute several programs simultaneously, and by modern standards in a unit of time modern system can execute more than several programs at once, here we are talking about dozens, hundreds of programs that are executed by the computer simultaneously. This is easy to imagine from a simple example. The factory employs one person who himself produces, say, matches. He prepares the wood himself, then he planes the matches himself, then dips them one by one in sulfur and finally packs them into boxes. How effectively do you think it works? And if you add another three dozen of the same workers, the efficiency of the plant will increase, do you think? And if everyone does their job: one to cook the wood, another to dip it, and a third to pack it, will the productivity of the plant increase? I think yes. This is precisely the principle on which multitasking is based. Multiplayer mode. This is something that is not fully implemented in the Windows system, but has long been implemented in Linux and even earlier implemented in UNIX. Multi-user mode is when several people can work on one computer at the same time. You and I know that a personal computer is personal because only one person can work on it. But operating systems are now designed in such a way that they allow servicing several users at the same time. True, this usually takes a lot of RAM. Let us recall the example of a match factory: one machine can simultaneously serve several employees.

Basic criteria for choosing an operating system.

New information and communication technologies are one of the most important factors, influencing the formation of society of the 21st century, the development of cultural diversity and universal human values.

The widespread dissemination of information technology has led to radical changes in all library activities related to serving users.

Modern libraries are transforming from repositories of printed documents into automated centers, digital libraries, electronic document delivery services available through email, global telecommunication systems. Along with this, regional libraries are one of the main information, cultural, educational and leisure centers of their regions.

A Multimedia Cultural Center has been created and has been successfully operating for 1.5 years in the Smolensk Regional Universal Library. The main goal of creating the center is to provide wider access for interested users to information on culture and art on the basis of modern information technologies, as well as to assist in the formation of a unified information and cultural space in our region.

The rationale for its creation was due to the appearance in the library’s collections of a significant number of storage units on non-traditional media. Today, the center's holdings include 13 thousand gramophone records, about 400 video cassettes, 300 audio cassettes, and more than 200 music and multimedia discs.

During the existence of the center, along with such organizations as television and radio companies, higher and secondary specialized educational establishments, creative unions, etc. became scientists, teachers and students, creative workers, amateurs various types arts

Today the center provides users with enough ample opportunities: listen to your favorite from the digitized archive of gramophone records, discover the treasures of the best museums and galleries in the world, visit memorable places, get acquainted with leading performers and their arrangements, choose from the collection of collections your favorite Russian film and theater classics, rarities - and all this without spending money for flights, moving, long searches for what you need.

The center operates a hardware and software complex for translating musical works, film and photo documents into digital view in the modern MPEG format, which allows not only to digitize funds and preserve them by creating an electronic database, but also enables non-traditional user access to a rich fund of archival audiovisual materials.

The complex was presented in sufficient detail in the report of our library on scientific and practical conferences ECHO SOUNDER 2001, 2002. There is no need to dwell in detail on the operation of the complex, but in a few words I will introduce the audience to its main functions.

margin-top:0cm" type="disc">alphabetical catalog (composer name); catalog of authors and titles (title piece of music).

In addition, there is an advanced search option;

auto RU; title; information about responsibility (performer of a musical work, instrumentalist, conductor); publisher (distributor); year of publication; content (concert, aria, from which operas, etc.); index of works.

One of essential functions The complex is the creation of insurance copies of already digitized materials, which makes it possible for their long-term storage and repeated use.

The program is accessible, has a user-friendly interface, and is intuitive, which simplifies user training and eliminates the need for special settings.

Information systems" href="/text/category/informatcionnie_sistemi/" rel="bookmark">information system solution is powerful enough in potential to provide a margin of safety and opportunities for expanding multimedia volumes.

Technically, a completely ordinary computer with sufficient big disk, but not extremely large - about 40-80 Gigabytes. Such a computer provides digitization work and houses a music archive. If the information volume is not enough, you can always deliver additional disks with large volume.

The requirements for workstations are not at all great - a personal computer with OS WIN 95/98 and sound card, because the user enters the details he is interested in, and the information is displayed in the form of multimedia.

A few words about the additional capabilities that the system has. First of all - versatility.

1. From the point of view of a unified view of the data that we receive from a variety of media. This system will be able to replace traditional record players, CDs, video discs, many media that have not yet become popular, such as DVD, and new digital video formats.

2. Universality of use for any PC model and not necessarily based on INTEL processors.

3. Versatility in terms of communication tools. In addition to a direct cable connection, a wide variety of remote access methods can be used in a local network, including INTERNET.

A little about the problems and difficulties we have encountered since the center began its work:

1. The problem of technical equipment, in terms of reproducing analog audio equipment. The main task is the translation into a digital field. It must be digitized first, and then the computer can be turned into a filter for the recording, allowing it to be edited or not edited to preserve its originality.

2. The problem of the quality of information digitization. The vast majority of storage units are limited edition gramophone records, which were produced in a fairly large quantity, but with a fairly limited high quality. Questions immediately arose - what is the goal - either digitization, high-quality processing and preservation of records, or digitization and ensuring free and easy access users to the fund. The solution to this problem, as we see it, lies in the creation of a specialized sound studio for the digitization of regional audio heritage as part of a corporate project. But this is a topic for a separate detailed conversation.

3. The issue of priority in selecting works for digitization. Due to the fact that there was no such experience at the beginning of the center’s work, it was decided to take the alphabetical catalog as a basis. Although this is probably one of the possible solutions. According to our statistics, from the total collection of about 13 thousand gramophone records, 1200 or 4800 phonograms have been digitized. This is due to the fact that with the center’s employees working on digitization for 2-3 hours every day, an average of 70-80 gramophone records or 250-300 phonograms are digitized per month.

4. It seems to us that the issue of standardizing the digitized funds of various organizations is very important, perhaps developing a unified legal framework in this direction, simpler than common “rules of the game.”

In conclusion, I would like to note that the digitization of audio funds, their preservation, the possibility of wide access to them on the basis modern technologies is one of the important and priority tasks. As the experience of our work shows, digitized audio funds are in demand, the process is developing, and we hope that our modest experience will serve as an example, and perhaps an impetus for the development of similar technologies, which in the future will provide the opportunity for intersystem and interregional integration in this area.

Operating system (OS) is an organized set of programs (systems) that acts as an interface between computer hardware and users. It provides users with a set of tools to facilitate the design, programming, debugging and maintenance of programs, while at the same time managing the allocation of resources to ensure efficient operation.

Operating systems (OS) are classified:

on the features of resource management algorithms – local And network OS. Local OSes manage resources separate computer. Network operating systems are involved in managing network resources;

by the number of simultaneously performed tasks - single-tasking And multitasking . Single-tasking operating systems perform the function of providing the user with virtual computer , making it simple and user-friendly interface

interaction with a computer, peripheral device management tools and files. Multitasking OS, in addition to the above functions, manages the division of shared resources such as the processor, RAM, files and external devices; by the number of simultaneously working users - And single-user multi-user

. The main difference between multi-user systems and single-user systems is the availability of means to protect each user’s information from unauthorized access by other users; if possible, parallelizing calculations within one task -

multithreading support . And A multi-threaded OS divides processor time not between tasks, but between their individual branches - threads; by the method of distributing processor time between several simultaneously existing processes or threads in the system -

non-preemptive multitasking preemptive multitasking . Multiprocessor operating systems, in turn, can be classified according to the way the computing process is organized in a system with a multiprocessor architecture: asymmetrical OS and symmetrical

OS. An asymmetric OS runs entirely on only one of the system processors, distributing application tasks across the remaining processors. A symmetric OS is completely decentralized and uses the entire set of processors, dividing them between system and application tasks; by hardware orientation - operating systems , personal computers , servers , mainframes ;

clusters depending on hardware platforms – And dependent mobile .;

In mobile operating systems, hardware-dependent places are localized in such a way that when the system is transferred to a new platform, only they are rewritten. A means to facilitate the transfer of an OS to another type of computer is to write it in a machine-independent language, for example, WITH , by specific areas of use - OS , batch processing time sharing

real time

. Batch processing systems are designed to solve computational problems that do not require quick results. The main goal and criterion for the effectiveness of batch processing systems is maximum throughput, that is, solving the maximum number of tasks per unit of time. In time-sharing systems, each user is provided with a terminal from which he can conduct a dialogue with his program. Each task is allocated a slice of processor time, so that no single task takes up the processor for too long. If the time slice is chosen to be small, then all users simultaneously working on one computer will have the impression that each of them is solely using the machine. Real-time systems are used to control various technical objects when there is a maximum permissible time during which a particular object control program must be executed. Failure to complete the program on time can lead to an emergency. Thus, the criterion for the effectiveness of real-time systems is their ability to withstand predetermined time intervals between launching a program and obtaining a result - a control action; . OSes using a monolithic kernel are compiled as one program, running in privileged mode and using fast transitions from one procedure to another, without requiring switching from privileged to user mode and vice versa. When building an OS based on a microkernel that operates in privileged mode and performs only a minimum of hardware management functions, the functions of more

high level run by specialized OS components - software servers running in user mode. With this design, the OS works more slowly, since transitions between privileged mode and user mode are often performed, but the system is more flexible and its functions can be modified by adding or excluding user mode servers; ;

based on object-oriented approach according to availability multiple application environments within a single OS, allowing you to run applications developed for multiple operating systems.

The concept of multiple application environments is most easily implemented in an OS based on the microkernel that is being worked on various servers , some of which implement the application environment of a particular operating system; By distribution of operating system functions among computers on the network. A distributed OS implements mechanisms that provide the user with the ability to imagine and perceive the network as a single-processor computer. Signs of a distributed OS are the presence of a single reference service for shared resources and a time service, the use of a call mechanism remote procedures

for distribution:

program procedures

by machine, multi-threaded processing, which allows you to parallelize calculations within one task and perform this task simultaneously on several computers on the network, as well as the presence of other distributed services.

The OS structure consists of the following modules

additional service programs (utilities) - make the process of communication between the user and the computer convenient and versatile.

In general, the operating system performs the following four functions:

provides other programs with a certain type of service (via utility programs), such as highlighting and memory assignment, synchronization of the calculation process and organization of the relationship between various processes in the computing system;

provides protection (to a certain extent) for other programs from the consequences of various special situations that arise during machine implementation this program, such as interruptions and machine failures;

implements, with varying degrees of complexity, the principle “ virtual machine”, which allows a group of programs to share computing resources, such as processor(s) and main memory;

organizes and monitors the implementation of management principles when solving such problems as ensuring data protection from unauthorized access and implementing a priority system for program access to computing resources.

Enables operation with long-term memory devices such as magnetic disks, ribbons, optical discs etc

Provides standard access to various input/output devices, such as terminals, modems, printing devices.

Provides some user interface.

Some systems are limited to the command line, while others are 90% user interface tools.

More advanced operating systems also provide the following features:

Parallel (more precisely, pseudo-parallel, if the machine has only 1 processor) execution of several tasks.

Distributing computer resources between tasks.

Organizing the interaction of tasks with each other.

Interaction of user programs with non-standard external devices.

Organization of machine-to-machine interaction and resource sharing. Protection system resources

, user data and programs, executing processes and itself from erroneous and malicious actions of users and their programs. Definition 1:Operating system

The operating system forms a self-contained environment that is not associated with any programming language. Any application program is associated with an operating system and can only be used on those computers that have a similar system environment(or the possibility of conversion - conversion of programs must be provided).

There are two approaches to considering the concept of OS.

Operating system as an extended machine : Using most computers at the machine language level is difficult, especially when it comes to input/output. For example, to organize reading a block of data from a floppy disk, a programmer can use 16 various teams, each of whichrequires13 parameters, such as the block number on the disk, the sector number on the track, etc. When the disk operation is completed, the controller returns 23 values reflecting the presence and types of errors, which obviously need to be analyzed. Even if you don't get into the course real problems input/output programming, it is clear that among programmers there would not be many who would be willing to directly engage in programming these operations. When working with a disk, the programmer-user only needs to represent it as a certain set of files, each of which has a name.

From this point of view, the function of the OS is providing the user with some extended or virtual machine that is easier to program and operate than the actual hardware that makes up the real machine.

Operating system as a resource management system: according to the second approach, the OS function is allocation of processors, memory, devices, and data among processes competing for these resources. The OS must manage all computer resources in such a way as to ensure maximum efficiency of its functioning.

Resource management involves solving two general tasks that do not depend on the type of resource:

resource planning - that is, determining to whom, when, and for divisible resources - and in what quantity it is necessary to allocate a given resource;

tracking the status of a resource - that is, maintaining operational information about whether the resource is busy or not busy, and for divisible resources - how much of the resource has already been distributed and how much is free.

Classification of operating systems

Let's consider the main functions of the OS for managing processors, memory, and external devices of a stand-alone computer.

1. Supports multitasking. Based on the number of simultaneously performed tasks, operating systems can be divided into two classes:

single-tasking (for example, MSDOS, MSX);

multitasking (EU OS, OS/2, UNIX, Windows 95).

Single-tasking OSes mainly perform the function of providing the user with a virtual machine, making the process of interaction between the user and the computer simpler and more convenient. Single-tasking operating systems include peripheral device management tools, file management tools, and user communication tools.

Multitasking The OS, in addition to performing the above functions, manages the division of shared resources such as the processor, RAM, files and external devices.

2. Supports multi-user mode. Based on the number of simultaneously working OS users, they are divided into:

for single-user (MSDOS, Windows 3.x,);

multi-user (UNIX, WindowsNT).

Preemptive and non-preemptive multitasking. The most important shared resource is processor time.

The method of distributing processor time between several simultaneously existing processes (or threads) in the system largely determines the specifics of the OS. Among the many existing options for implementing multitasking, two groups of algorithms can be distinguished:

non-preemptive multitasking;

preemptive multitasking Multithreading support.

An important property of the OS is the ability to parallelize calculations within a single task. A multi-threaded OS divides processor time not between tasks, but between their individual branches (threads). Multiprocessing. Another important property of the OS is the absence or presence of multiprocessing support in it - multiprocessing.

Multiprocessing leads to the complication of all resource management algorithms.

Purpose of the operating system: Operating system (OS) is a set of system and control programs designed for the most effective use all resources of a computer system (CS) (A computer system is an interconnected set of hardware computer technology And software

The purpose of the OS is to organize the computing process in a computer system, rational distribution of computing resources between the individual tasks being solved; providing users with numerous service tools that facilitate the process of programming and debugging tasks. The operating system plays the role of a kind of interface (Interface is a set of means for pairing and communicating computer devices that provide them effective interaction) between the user and the aircraft, i.e. The OS provides the user with a virtual aircraft. This means that the OS largely forms the user’s idea of the capabilities of the aircraft, the ease of working with it, and its throughput. Different OS on the same technical means can provide the user with various options for organizing the computing process or automated processing data.

In computer software, the operating system occupies a central position because it plans and controls the entire computing process. Any of the software components must run under the OS.

Classification of operating systems:

Operating systems may differ in implementation features internal algorithms management of the main computer resources (processors, memory, devices), features of the design methods used, types of hardware platforms, areas of use and many other properties.

Depending on the features of the processor control algorithm used, operating systems are divided into multi-tasking and single-tasking, multi-user and single-user, systems that support multi-threaded processing and those that do not, multi-processor and single-processor systems.

Based on the number of simultaneously performed tasks, operating systems can be divided into two classes:

1. single-tasking;

2. multitasking.

Single-tasking operating systems mainly perform the function of providing the user with a virtual machine, making the process of interaction between the user and the computer simpler and more convenient. Single-tasking operating systems include peripheral device management tools, file management tools, and user communication tools.

Multitasking OS, in addition to the above functions, manages the division of shared resources such as the processor, RAM, files and external devices.

Multitasking operating systems are divided into three types in accordance with the efficiency criteria used in their development:

1. batch processing systems;

2. time sharing systems;

3. real-time systems.

Batch processing systems were intended to solve problems primarily of a computational nature that did not require quick results. The main goal and criterion for the effectiveness of batch processing systems is maximum throughput.

Time-sharing systems are designed to correct the main drawback of batch processing systems - the isolation of the user-programmer from the process of performing his tasks. Each user of the time sharing system is provided with a terminal from which he can conduct a dialogue with his program.

Real-time systems are used to control various technical objects. The efficiency criterion for real-time systems is their ability to withstand predetermined time intervals between launching a program and obtaining a result (control action). This time is called the reaction time of the system, and the corresponding property of the system is called reactivity.

Some operating systems may combine the properties of systems different types, for example, some tasks can be performed in batch processing mode, and some in real time or time sharing mode. In such cases, batch processing mode is often called background mode.

Based on the number of concurrent users, operating systems are divided into:

1. single-user;

2. multi-user.

The main difference between multi-user systems and single-user systems is the availability of means to protect each user’s information from unauthorized access by other users. It should be noted that not every multitasking system is multi-user, and not every single-user OS is single-tasking.

Among the many existing options For the implementation of multitasking, two groups of algorithms can be distinguished:

1. non-preemptive multitasking;

2. preemptive multitasking.

The main difference between preemptive and non-preemptive multitasking is the degree of centralization of the process scheduling mechanism. In the first case, the process scheduling mechanism is entirely concentrated in the operating system, and in the second, it is distributed between the system and application programs. With non-preemptive multitasking, the active process runs until it, on its own initiative, gives control to the operating system so that it selects another process ready to run from the queue. With preemptive multitasking, the decision to switch the processor from one process to another is made by the operating system, and not by the active process itself.

The properties of the operating system are directly influenced by the hardware on which it is designed. Based on the type of hardware, operating systems of personal computers, minicomputers, mainframes, clusters and computer networks are distinguished. Among the listed types of computers, there can be both single-processor and multiprocessor options. In any case, the specifics of the hardware are usually reflected in the specifics of the operating systems.

So, depending on the processor control algorithm, operating systems are divided into:

1. Single-tasking and multi-tasking

2. Single-user and multi-user

3. Uniprocessor and multiprocessor systems

4. Local and network.

Based on the number of simultaneously performed tasks, operating systems are divided into two classes:

1. Single-tasking (MS DOS)

2. Multitasking (OS/2, Unix, Windows)

Single-tasking systems use peripheral device management tools, file management tools, and means of communicating with users. Multitasking OSes use all the features found in single-tasking OSes and also manage the division of shared resources: processor, RAM, files, and external devices.

Depending on the areas of use, multitasking operating systems are divided into three types:

1. Batch processing systems (OS EC)

2. Time-sharing systems (Unix, Linux, Windows)

3. Real time systems (RT11)

Batch processing systems are designed to solve problems that do not require quick results. The main goal of a batch processing OS is maximum throughput or solving the maximum number of tasks per unit of time.

These systems provide high performance when processing large amounts of information, but reduce the user's efficiency in interactive mode.

In time-sharing systems, each task is allocated a small amount of time to complete, and no single task occupies the processor for long. If this period of time is chosen to be minimal, then the appearance of simultaneous execution of several tasks is created. These systems have less throughput, but provide high user efficiency in interactive mode.

Real-time systems are used to control technological process or a technical object, for example, an aircraft, a machine tool, etc.

Based on the number of simultaneously working users on a computer, operating systems are divided into single-user (MS DOS) and multi-user (Unix, Linux, Windows 95 - XP)

In multi-user operating systems, each user customizes the user interface for himself, i.e. can create his own sets of shortcuts, groups of programs, set individual color scheme, move to comfortable spot taskbar and add new items to the Start menu.

In multi-user operating systems, there are means to protect each user's information from unauthorized access by other users.

Multiprocessor and single-processor operating systems. One of the important properties of the OS is the presence in it of support for multiprocessing data processing. Such tools exist in OS/2, Net Ware, and Windows NT. Based on the way the computing process is organized, these operating systems can be divided into asymmetric and symmetric.

One of the most important features of the classification of computers is their division into local and network. Local OSes are used on standalone PCs or PCs that are used in computer networks as a client.

The local OS includes a client part of the software for accessing remote resources and services. Network operating systems are designed to manage the resources of PCs connected to a network for the purpose of sharing resources. They provide powerful means of restricting access to information, its integrity and other possibilities for using network resources.

26. Operating system module

The OS structure consists of the following modules:

basic module (OS kernel) - controls the operation of the program and the file system, provides access to it and exchange of files between peripheral devices;

command processor- decrypts and executes user commands received primarily through the keyboard;

peripheral drivers- software ensures consistency between the operation of these devices and the processor (each peripheral device processes information differently and at a different pace);

additional service programs(utilities) - make the process of communication between the user and the computer convenient and versatile.

OS loading. The files that make up the OS are stored on disk, which is why the system is called disk operating system (DOS). It is known that in order to execute them, programs - and, therefore, OS files - must be located in random access memory (RAM). However, in order to write the OS into RAM, you need to run a boot program, which is not in RAM immediately after turning on the computer. The way out of this situation is to sequentially, step-by-step load the OS into RAM.

The first stage of loading the OS. IN system unit The computer contains a read-only memory device (ROM, read-only memory, ROM-Read Only Memory - memory with read-only access), which contains programs for testing computer blocks and the first stage of loading the OS. They begin to execute with the first current pulse when the computer is turned on. At this stage, the processor accesses the disk and checks for the presence of a very small program - the boot loader - at a certain place (at the beginning of the disk). If this program is detected, it is read into RAM and control is transferred to it.

The second stage of loading the OS. The bootloader program, in turn, searches the disk for the base OS module, rewrites its memory and transfers control to it.

The third stage of loading the OS. The base module includes a main bootloader that searches for other OS modules and reads them into RAM. After the OS has finished loading, control is transferred to the command processor and a system prompt for entering a user command appears on the screen.

Note that the basic OS module and the command processor must be in the RAM while the computer is running. Therefore, there is no need to load all OS files into RAM at the same time. Device drivers and utilities can be loaded into RAM as needed, reducing the required amount of RAM allocated to system software.

27. Composition of the operating system .

The MS-DOS operating system consists of many various files. They include the actual operating system files IO.SYS, MSDOS.SYS and the command processor COMMAND.COM. In addition to these three files, which represent a working MS-DOS kernel, the operating system distribution includes files of so-called external commands, for example FORMAT, FDISK, SYS, drivers various devices and some other files.

The IO.SYS file contains an extension to the basic input/output system and is used by the operating system to interact with the computer hardware and BIOS.

The MSDOS.SYS file is in a sense a set of interrupt handling programs, in particular the INT 21H interrupt.

The COMMAND.COM command processor is designed to organize a dialogue with the computer user. It analyzes commands entered by the user and organizes their execution. The so-called internal commands - DIR, COPY, etc. are processed by the command processor.

The remaining operating system commands are called external commands. External commands are so named because they are located in separate files. Operating system external command files contain utility programs for performing a variety of operations, such as formatting disks, sorting files, and printing texts.

Drivers (usually files with the extension SYS or EXE) are programs that support various hardware. The use of drivers easily solves the problems of using new equipment - just connect the appropriate driver to the operating system.

Application programs interact with the device through the driver, so they will not change when the hardware changes. For example, new disk device may have a different number of tracks and sectors, different control commands. All this is taken into account by the driver, and the application program will work with the new disk as before, using DOS interrupts.

The operating system files IO.SYS, MSDOS.SYS and COMMAND.COM must be written to a specific location on the disk. You should not copy them to other directories on the disk.

If you need to make a boot floppy disk with which you can boot MS-DOS on your computer, it is not enough to simply copy the main operating system files - IO.SYS, MSDOS.SYS and COMMAND.COM - onto the floppy disk.

To make a system floppy disk, you must use either the FORMAT or SYS commands, or special programs, such as Safe Format from Norton Utilities.

The most in a simple way to make a blank floppy disk bootable is to use an external MS-DOS commands- SYS. To use it, insert a blank floppy disk into the drive and from the root directory of drive C: issue the command:

After executing the SYS command, the floppy disk will contain the files IO.SYS, MSDOS.SYS and COMMAND.COM written to certain places floppy disks. You can boot MS-DOS from this floppy disk if you insert the system floppy disk into drive A: before turning on the power.

28. Operating system boot process

When the computer is turned on, control is transferred to basic system I/O, BIOS. It checks the computer's hardware components, forms the initial part of the interrupt vector table, initializes devices and begins the process of loading the operating system.

Booting begins with the BIOS attempting to read the very first sector of the floppy disk inserted into drive A: (on boot diskette This sector contains the operating system boot loader). If a system floppy disk is inserted into the drive, the bootloader is read from it and control is transferred to it.

If the floppy disk is not a system one, i.e. does not contain a boot record, a message appears on the screen asking you to replace the floppy disk.

If there is no floppy disk in drive A: at all, then the BIOS reads the master boot record of drive C: ( Master Boot Record). This is usually the very first sector on the disk. Control is transferred to the loader, which is located in this sector. The bootloader analyzes the contents of the partition table (also located in this sector), selects the active partition and reads the boot record of this partition. Boot entry active partition (Boot Record) is similar to the boot record located in the first sector of the system floppy disk.

The active partition's boot record reads the IO.SYS and MSDOS.SYS files from disk (in that order). Resident drivers are then read and loaded. The linked list of device drivers begins to be generated. The contents of the CONFIG.SYS file are analyzed and the drivers described in this file are loaded. First, the drivers described by the DEVICE parameter are loaded, then (only in MS-DOS versions 4.x and 5.0) the resident programs specified by the INSTALL statements. After this, the command processor is read and control is transferred to it.

The command processor consists of three parts - resident, initializing and transit. The resident part is loaded first. It processes interrupts INT 22H, INT 23H, INT 24H, and controls the loading of the transit part. This part command processor processes MS-DOS errors and prompts the user for action when errors are detected.

The initialization part is used only during the boot process of the operating system. It defines the starting address at which it will load user program and initiates execution of the AUTOEXEC.BAT file.

The transit part of the command processor is located in the highest memory addresses. This part contains handlers internal teams MS-DOS and interpreter batch files with name extension .BAT. The transit part issues a system prompt (for example, A:>), waits for operator command input from the keyboard or from batch file and organizes their implementation.

After loading the command processor and completing the initial procedures listed in the AUTOEXEC.BAT file, the system is ready for operation.

29. System files operating system

If in the team FORMAT line the /s parameter is specified, then
A formatted disk records copies of system files. MS-DOS has
three system files - IO.SYS, MSDOS.SYS and COMMAND.COM. On PC-DOS system
the IO.SYS file is called IBMBIO.COM, and the MSDOS.SYS file is called IBMDOS.COM.
System files are stored on the disk from which the operating system is loaded
system. Files are written in a strictly defined order and have strictly
specific location.
IO.SYS is located directly after the disk directory. File
contains working operating system drivers. A driver is a program
in machine code that provides an interface between the operating system and
peripheral device(see chapter 14). Since IO.SYS is responsible for communication with
physical devices, then it must be perfectly matched to
specific system and is therefore usually organized by the manufacturer.
MSDOS.SYS is written directly after the IO.SYS file. MSDOS.SYS
is the kernel of the operating system. The file selects all requests for service
services (such as opening or reading a file) and transfers them to the file
IO.SYS. The protocol for interaction between MSDOS.SYS and IO.SYS is identical to the protocol
interaction between two operating systems. Therefore, it is considered that the file
MSDOS.SYS is independent of electronic equipment ( external devices And
the computer itself).
The COMMAND.COM file is an MS-DOS command interpreter. He serves
interface between the operating system and the user. File Commands
display a standard system request, process messages sent from
keyboard commands (translated into machine code), etc. COMMAND.COM
consists of three components: resident, variable and initializing.

30. Operating system commands

DOS commands for working with directories
Change current directory
Browse the catalog
Creating a directory
Removing a directory
Renaming a directory
Setting a directory listing to search for running programs

Changing the current directory
Command Format:
cd [drive:][path]
Examples:
cd \ - goes to the root directory of the current disk;
cd \exe - go to the exe directory in root directory;

Browse the catalog
Command Format:
dir [drive:][path\][filename] [options]
Options:
/p - screen-by-screen output;
/w - output in wide format;
/s - table of contents of the directory specified in the command and all its subdirectories;
/b - only file names without header and summary information;
/aattribute - information about files that have the specified attributes.
Sorting:
/on - by name;
/oe - by extension;
/od - by time;
/og - first display information about subdirectories;
Examples:
dir - table of contents of the current directory
dir *.exe - information about all .exe files in the current directory