Operating system meaning and composition. Installing multiple systems and using virtual machines
So, what is an operating system on a computer? The OS is the most important software that runs on a computer. It manages memory, processes, and all software and hardware. We can say that the OS is a bridge between a computer and a person. Because without an operating system, a computer is useless.
Apple Mac OS X
Mac OS is a line of operating systems created by Apple. It comes pre-installed on all new Macintosh or Mac computers. Latest versions this operating system are known as OS X. Namely Yosetime(released in 2014), Mavericks (2013), Mountain Lion (2012), Lion(2011), and Show Leopard(2009). There is also Mac OS X Server, which is designed to run on servers.
According to general statistics StatCounter Global Stats, percentage Mac users OS X makes up 9.5% of the operating system market, as of September 2014. This is much lower than the percentage Windows users(almost 90% ). One of the reasons for this is that Apple computers very expensive.
Linux
Linux is a family of open-source operating systems source code. This means they can be modified (changed) and distributed by anyone around the world. This makes this OS very different from others such as Windows, which can only be modified and distributed by the owner (Microsoft). The advantages of Linux are that it is free and there are many different versions to choose from. Each version has its own appearance, and the most popular of them are Ubuntu, Mint And Fedora.
Linux is named after Linus Torvalds, who laid the foundation for Linux in 1991.
According to general statistics from StatCounter Global Stats, the percentage Linux users accounts for less than 2% of the operating system market, as of September 2014. However, due to flexibility and ease of configuration, most servers run on Linux.
Operating systems for mobile devices
All the operating systems we talked about above are designed for desktop and laptop computers, such as a laptop. There are operating systems that are designed specifically for mobile devices, such as phones, and MP3 players, for example, Apple, iOS, Windows Phone And Google Android. In the picture below you can see Apple iOS running on an iPad.
Of course, they are not as functional as computer operating systems, but they are still capable of performing many basic tasks. For example, watching movies, browsing the Internet, running applications, games, etc.
That's all. Leave in the comments what operating system you use and why you like it
Operating systems: purpose and main functions
Operating System Concept
Operating system (OS) is a set of programs that ensure the interaction of all hardware and software parts of the computer with each other and the interaction between the user and the computer.
The OS ensures the holistic functioning of all computer components and also provides the user with access to the computer’s hardware capabilities. operating system is a basic and necessary component of computer software; without it, a computer cannot operate in principle.
OS composition
The OS structure consists of the following modules:
base module (OS kernel)- manages the operation of programs and the file system, provides access to it and exchange of files between peripheral devices;
T.e. translates commands from a program language into a “machine code” language that a computer can understand
command processor- deciphers and executes user commands received primarily through the keyboard;
T.e. asks the user for commands and executes them. The user can give, for example, a command to perform some operation on files (copying, deleting, renaming), a command to print a document, etc.
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);
T.e. special programs, which provide control over the operation of devices and coordination of information exchange with other devices. Each device has its own driver.
additional service programs(utilities) - make the process of communication between the user and the computer convenient and versatile
those. Such programs allow you to maintain disks, perform operations with files, work in computer networks, etc.
Purpose of the Operating System
The OS is designed to solve the following tasks:
computer hardware maintenance;
creating a working environment and user interface;
execution of user commands and program instructions;
organization of input/output, information storage and
file and data management.
According to the definition, all tasks solved by the OS can be divided into two groups:
providing the user or programmer, instead of real computer hardware, with an extended virtual (i.e., not really existing) machine, which is more convenient to work with and easier to program;
increasing the efficiency of using a computer by rationally managing its resources in accordance with some criterion.
Operating System Features
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 (input and data output, starting and stopping other programs, allocating and freeing additional memory, etc.).
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 hard disk, optical discs etc.), organized in one or another file system.
Providing a user interface.
Network operations, support for the network protocol stack.
Additional functions:
Parallel or pseudo-parallel execution of tasks (multitasking).
Efficient distribution of computing system resources between processes.
Access control 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.
Evolution of operating systems and basic ideas
The predecessor of the OS should be considered utility programs (bootloaders and monitors), as well as libraries of frequently used routines, which began to be developed with the advent of universal computers 1st generation(late 1940s). Utilities minimized the operator's physical manipulation of the equipment, and libraries made it possible to avoid repeated programming of the same actions (carrying out I/O operations, calculating mathematical functions, etc.).
In the 1950s and 60s, the main ideas that determined the functionality of the OS were formed and implemented: batch mode, time sharing and multitasking, separation of powers, real time, file structures and file systems.
operating systemDOS
DOS is the first operating system for personal computers, which became widespread and was the main one for IBM PC computers from 1981 to 1995. Over time, it was practically supplanted by new, modern operating systems Windows and Linux, but in some cases DOS remains convenient and the only way to work on a computer (for example, in in cases where the user works with outdated equipment or software written a long time ago, etc.)
Users work with the DOS operating system using the command line; it does not have its own graphical interface. The DOS OS has made it possible to successfully work with a PC for 15 years, however, this work cannot be called convenient. DOS acted as an “intermediary” between the user and the computer and helped turn complex commands for accessing disks into simpler and more understandable ones, but as it developed, it itself became “overgrown” with an abundance of commands and began to hinder work with the computer. This is how the need for a new intermediary arose - this is how shell programs appeared.
A shell is a program that runs under the OS and helps the user work with the OS. The shell program clearly shows the entire file structure of the computer: disks, directories, files. Files can be searched, copied, moved, deleted, sorted, modified and launched with just a few keys. One of the most common is Norton Commander(NC). The graphical shells of Windows 3.1 and Windows 3.11 use the concept of so-called “windows” that can be opened, moved around the screen, and closed. These windows “belong” to various programs and reflect their work.
DOS uses the FAT file system. One of its disadvantages is the restrictions on file and directory names. The name can contain no more than 8 characters. In addition, DOS does not distinguish between lowercase and uppercase letters of the same name.
Since DOS was created a long time ago, it does not meet the requirements of modern operating systems today. It cannot directly use the large amounts of memory installed in modern computers.
Operating system MICROSOFT WINDOWS
Graphical shells Widows 1.0, Widows 2.0, Widows 3.0, Widows 3.1 and Widows 3.11 ran under MS DOS, that is, they were not independent operating systems. But since the advent of Windows opened up new possibilities, Windows is called not a shell, but an environment.
The Windows environment is characterized by the following features that distinguish it from other shell programs:
Multitasking;
Unified software interface;
Unified user interface;
Graphical user interface;
Unified hardware-software interface.
To replace the operating room DOS system with its graphical shells Windows 3.1 and Windows 3.11 came full-fledged operating systems of the MS Windows family (first Windows 95, then Windows 98, Windows 2000, Windows XP). Unlike Windows 3.1 and Windows 3.11, they start automatically after you turn on the computer.
In MS Windows, the FAT–VFAT file modification is used to store files. In it, the length of file and directory names can reach 256 characters.
In Windows OS, the mouse is widely used when working with windows and applications; in MS DOS, only the keyboard is used.
MSWindows also has a Taskbar. It makes the multitasking mechanism clearer and greatly speeds up the process of switching between applications.
Worker Windows table designed to make the job as easy as possible for the novice user, while at the same time providing maximum customization options to suit the specific needs of experienced users.
Operating system LINUX
Linux is an operating system for IBM-compatible personal computers and workstations. It is a multi-user operating system with a networked graphical window, the X Window System. The Linux operating system supports open systems standards and Internet protocols and is compatible with Unix, DOS, and MS Windows systems.
As a traditional operating system, Linux performs many of the same functions as DOS and Windows, but the operating system is particularly powerful and flexible. Linux brings the speed, efficiency and flexibility of UNIX to the PC user, while taking advantage of all the benefits of a personal computer. When working with the mouse, all three buttons are actively used, in particular, the middle button is used to insert text fragments.
By using Linux systems You can turn any personal machine into a workstation. Nowadays, Linux is the operating system for business, education and individual programming.
OSUNIX
UNIX is a group of portable, multitasking and multi-user operating systems.
First UNIX system was developed in 1969 by AT&T's Bell Labs division. Since then, a large number of different UNIX systems have been created.
Some distinctive features of UNIX systems include:
use of simple text files to configure and manage the system;
widespread use of utilities launched on the command line;
interaction with the user through a virtual device - a terminal;
presentation of physical and virtual devices and some interprocess communication tools as files;
using pipelines of several programs, each of which performs one task.
UNIX systems are of great historical importance because they spread some of today's popular OS concepts and approaches and spread some of today's popular OS concepts and approaches. software. Also, during the development of UNIX systems, the C language was created.
An OS is a set of interrelated programs designed to improve the efficiency of computer hardware by rationally managing its resources, as well as to provide convenience to the user by providing him with an extended virtual machine.
The main resources managed by the OS include processes, main memory, timers, data sets, disks, tape drives, printers, network devices, and some others. I use different operating systems to solve resource management problems. various algorithms, the features of which ultimately determine the appearance of the OS.
So, the requirements for network operating systems today include: functional completeness and efficient resource management, modularity and extensibility, portability and multi-platform, compatibility at the application and user interface level, reliability, fault tolerance, security and performance.
Types of operating systems. We all constantly hear such phrases as “operating system” and “Windows”, but few people understand what they mean we're talking about. When I am asked to help in some matter, and I ask a person what operating system they have on their computer, they answer me that they either do not understand what they are talking about, or they honestly say that they do not know. It is imperative to know what operating system is installed on your computer, because... They are all different and their settings are different. And if you want to learn something from computer topics, then you must understand this and be able to identify your operating system. We will also consider this issue in our lesson.
First, we need to understand what an operating system is and what it is designed for.
Operating system, abbr. OS (English operating system, OS) is a set of interconnected programs designed to manage computer resources and organize user interaction. (Wikipedia)
Without an operating system (OS for short), not a single computer will even work. It is the operating system that controls all the programs, processes, memory and all the hardware on your computer.
As soon as you turn on the computer, the process of loading the operating system begins, during which the following occurs:
- Checking all equipment.
- Availability of drivers for them. A driver is a program for the operation of each equipment separately. Each operating system has its own driver written.
- After the first two checks are completed, the operating system starts.
Types of operating systems
Most often, when you buy a computer, the operating system is already installed. Most of you don't even care about what she is like. And knowing your system is very important, if only because different operating systems work differently, are configured differently, and even have a different desktop.
There are three main and most popular operating systems:
Microsoft Windows(Microsoft is the company that produces this system, and Windows (Windows), translated from English, means windows):
Apple Mac OS X(abbreviated as Mac, and Apple is a company (translated from English, it means apple);
Each operating system has its own type, the so-called GUI(from English - face).
The first operating systems, called MS-DOS, did not have a graphical interface. Work in them was only through command line using the keyboard. There were no mice then, and they weren’t needed. It was necessary to know and remember many commands on English language. And on the monitor there were only numbers and letters, at best, graphs. For a simple user all this was not clear and not interesting.
In the mid-1980s Microsoft company created an operating room Windows system, and a new era began, thanks to which you and I can now write letters, books, work with photographs, pictures, create our own films, websites, “walk” on the Internet and learn new sciences and crafts on the computer.
Here is the list of Windows OS:
- Windows 1.0 (1985)
- Windows 2.0 (1987)
- Windows 3.0 (1990)
- Windows 3.1 (1992)
- Windows for Workgroups 1/3.11
The Windows 9x family, in which people like you and I could already work:
- Windows 95 (1995)
- Windows 98 (1998)
- Windows ME (2000)
Windows NT family
- Windows NT 3.1 (1993)
- Windows NT 3.5 (1994)
- Windows NT 3.51 (1995)
- Windows NT 4.0 (1996)
- Windows 2000 - Windows NT 5.0 (2000)
- Windows XP - Windows NT 5.1 (2001)
- Windows XP 64-bit Edition - Windows NT 5.2 (2003)
- Windows Server 2003 - Windows NT 5.2 (2003)
- Windows XP Professional x64 Edition - Windows NT 5.2 (2005)
- Windows Vista - Windows NT 6.0 (2006)
- Windows Home Server - Windows NT 5.2 (2007)
- Windows Server 2008 - Windows NT 6.0 (2008)
- Windows Small Business Server - Windows NT 6.0 (2008)
- Windows 7 - Windows NT 6.1 (2009)
- Windows Server 2008 R2 - Windows NT 6.1 (2009)
- Windows Home Server 2011 - Windows NT 6.1 (2011)
- Windows 8 - Windows NT 6.2 (2012)
- Windows Server 2012 - Windows NT 6.2 (2012)
- Windows 8.1 - Windows NT 6.3 (2013)
- Windows Server 2012 R2 - Windows NT 6.3 (2013)
- Windows 10 - Windows NT 10.0 (2015)
OS family for smartphones.
List of questions for the exam in the OS discipline 2013/14 academic year. Year 1. Definition of OS. Purpose and functions of the operating system.
An operating system is a set of interconnected programs that ensure user interaction with a computer system, as well as management of computer system resources. Functions:
Providing the user with a virtual machine (virtual hardware) instead of real hardware;
Increased efficiency of equipment use through rational use
resources.
Resources: memory, processor time, input/output devices.
The OS regulates conflicts that arise between processes when sharing resources. The OS satisfies requests for resources, taking into account their availability or occupancy.
2. Place of the OS in the structure of the computing system.
A computing system is a hardware and software complex that provides services to the user.
Figure 1. Computer system structure
Application programs
Programming systems
Logical Device Management
Physical device management
Hardware
Table 1. Computing system
Hardware - the lower level is equipment, what is made of metal, plastic and other materials used to produce computer hardware.
Physical devices are controlled by programs that focus on the qualities and properties of the equipment, interact with hardware structures, and know the “language” of the equipment.
Reactivity (guaranteed system reaction time to a particular event)
The main goal and criterion for the effectiveness of batch processing systems is maximum throughput, i.e. solving the maximum number of problems per unit of time. To achieve this goal, batch processing systems use the following operating scheme: at the beginning of work, a package of tasks is formed, each task contains requirements for system resources; from this package a multiprogram mixture is formed, that is, many simultaneously performed tasks. For simultaneous execution, tasks are selected that have different resource requirements, so as to ensure a balanced load on all devices of the computer. The choice of a new task from a package of tasks depends on the internal situation in the system. Consequently, in computing systems running batch OSes, it is impossible to guarantee the completion of a particular task within certain period time.
The purpose of scheduling in time sharing systems is to improve user convenience and efficiency. In time-sharing systems, users (or one user) are given the opportunity to interact interactively with several applications at once. The OS forces applications to periodically pause without waiting for them to voluntarily release the processor. All applications are allocated CPU quantum on a rotating basis.
Interactive OS (Time Sharing OS)
Real time OS
OS class
Batch OS
User experience
Efficiency criteria and OS classes.
conflict resolution between processes
status tracking and resource usage accounting
satisfying resource requests
resource planning (when, to whom and to what extent)
e.g. CD)
Resource management includes solving the following tasks:
The logical device control layer is user-oriented, designed to smooth out the hardware features of the devices. Commands at this level refer to the previous layer.
A programming system is a set of programs to support the entire technological cycle of software development.
Application programs are designed to solve certain problems in specific areas of knowledge. The OS includes the second and third levels of the pyramid.
3. The concept of resource. Resource management in a computing system.
A resource is any object that can be distributed within the OS.
processors (processor time)
peripheral devices (disks, timers, data sets, printers, network devices and
Resources can be:
shared (multiple processes use them at the same time) and indivisible
pageable (can be taken away from a process without negative consequences– for example, RAM) and non-paged (forced pageout leads to failure –
time, in such a way that users who have launched programs for execution are able to maintain a dialogue with them.
Real-time operating systems are designed to control various technical objects or technological processes. In such systems, a multiprogram mixture usually represents a fixed set of pre-developed programs, and the selection of a program for execution is carried out by interrupts (based on the state of the controlled object) or in accordance with the schedule of planned work. The criterion for the effectiveness of a real-time OS is the ability of the system to withstand predetermined time intervals between launching a program and obtaining the result (system reactivity).
5. Evolution of the OS.
First period (1945 -1955). In the mid-40s, the first tube computing devices were created (in the USA and Great Britain), in the USSR the first tube Calculating machine appeared in 1951. Programming was carried out exclusively in machine language. Element base– electronic tubes and communication panels. There were no operating systems; all tasks of organizing the computing process were solved manually by the programmer from the control panel. System software - libraries of mathematical and utility routines.
Second period (1955 - 1965). Since the mid-50s, a new period in development began computer technology associated with the emergence of a new technical base- semiconductor elements (transistors). During these years the first algorithmic languages and, therefore, the first system programs are compilers. The cost of CPU time has increased, requiring a reduction in the time overhead between program runs. The first batch processing systems appeared, increasing the processor load factor. Batch processing systems were the prototype of modern operating systems; they became the first system programs, designed to control the computing process. Was developed formal language task management. A virtual memory mechanism has appeared.
Third period (1965 - 1975). Transition to integrated circuits. Creation of families of software-compatible machines (IBM System/360 series of machines, Soviet analogue - EC series machines). During this period of time, almost all the basic concepts inherent in modern operating systems were implemented: multiprogramming, multiprocessing, multi-terminal mode, virtual memory, file system, access control and networking. The processors now have privileged and user modes of operation, special registers for context switching, means of protecting memory areas, and an interrupt system. Another innovation is spooling. Spooling at that time was defined as a way of organizing the computing process, according to which tasks were read from punched cards onto disk at the pace at which they appeared in the computer center, and then, when the next task was completed, a new task was loaded from disk into the free partition . Appeared new type OS - time sharing systems. At the end of the 60s, work began on creating the global ARPANET network, which became the starting point for the Internet. By the mid-70s, minicomputers became widespread. Their architecture was significantly simplified compared to mainframes, which was reflected in their OS. The cost-effectiveness and accessibility of mini-computers served as a powerful incentive to create the first local networks. Since the mid-70s, the widespread use of the UNIX OS began. In the late 70s, a working version of the TCP/IP protocol was created, and in 1983 it was standardized.
Fourth period (1980–present). The next period in the evolution of operating systems is associated with the emergence of large integrated circuits(BIS). During these years, there was a sharp increase in the degree of integration and a reduction in the cost of microcircuits. The era of personal computers has arrived. Computers have become widely used by non-specialists. A graphical user interface (GUI) has been implemented, the theory of which was developed back in the 60s. WITH
1985 Windows began to be released, it was graphical shell MS-DOS until 1995, when the full-fledged Windows 95 operating system was released. IBM and Microsoft jointly developed the OS/2 operating system. She supported preemptive multitasking, virtual memory, graphic user interface, a virtual machine for running DOS applications. The first version was released in 1987. Subsequently, Microsoft abandoned OS/2 and began Windows development N.T. The first version was released in 1993.
IN 1987 The MINIX operating system (LINUX prototype) was released; it was built on the principle of microkernel architecture.
In the 80s, the main standards for communication equipment for local networks were adopted: in 1980 - Ethernet, in 1985 - Token Ring, in the late 80s - FDDI. This made it possible to ensure compatibility of network operating systems at lower levels, as well as to standardize the operating system interface with network adapter drivers.
In the 90s, almost all operating systems became network-based. Specialized operating systems have appeared that are designed exclusively for solving communication problems (IOS from Cisco Systems). Appearance World services Wide Web(WWW) in 1991 gave a powerful impetus to the popularity of the Internet. The development of corporate network operating systems is coming to the fore. Mainframe OS development is resuming. In 1991 LINUX was released. A little later, FreeBSD was released (the basis for it was BSD UNIX).
6. The current stage of OS development.
In the 90s, almost all operating systems became network-based, and these functions were included in the kernel. Fully compatible with major local and global networks. Over the past decade, special attention has been paid to corporate network operating systems. Their further development represents one of the most important tasks in the foreseeable future. For such networks, it is important to have centralized administration and management tools. It is also important for them, due to their heterogeneity, to have and follow multiple standards.
Also, at the present stage of OS development, security tools have come to the fore. Multi-platform (portability) is of great importance. The convenience of a person working with a computer increases.
7. Functional components of a personal computer OS.
1) Processor management subsystem: distributes processor time, creates and destroys processes, creates a process context, allocates resources to processes, synchronizes processes, implements inter-process communication.
2) Memory management subsystem: organizes virtual memory, monitors free and used memory, allocates memory to processes and frees it, configures program addresses on desired area physical memory, dynamic selection memory, memory protection (hardware and software), memory defragmentation possible.
3) File management subsystem and external devices: storing data on disks, organizing parallel operation of input/output devices, coordinating data exchange rates between the processor and devices, separating devices and data between processes, organizing user-friendly interface for other parts of the system, support for a wide range of drivers and short startup times the required driver upon detection desired device, support for multiple file systems, as well as synchronous and asynchronous operations.
4) Data protection and administration: protection against hardware failures (redundancy), software errors, protection against unauthorized access, logical login procedure (authentication), confirmation of access rights (authorization), audit tools
5) Application Programming Interface
operating system- a set of software that provides control of computer hardware and application programs, as well as their interaction with each other and the user.
The OS forms a stand-alone 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. Applied software, developed in the environment of one operating system, cannot be used to work in the environment of another operating system, unless there is a special set of programs (converter) that allows this to be done. In this case, they talk about software incompatibility of computers.
1. OS location in general structure computer.
A modern computer system consists of one or more processors, RAM, disks, keyboard, monitor, printers, network interface and other devices, i.e. is a complex complex system. Writing programs that monitor all components, use them correctly, and still perform optimally is an extremely difficult task. For this reason, computers are equipped with a special layer of software called an operating system. The OS is responsible for managing all of the listed devices and provides the user with programs that have simple, accessible interface for working with equipment. Compound computer system can be roughly divided into three levels:
§ hardware level;
§ system level;
§ software level.
Ticket number 2 The concept of an operating system. Classification of operating systems
operating system-- a program that boots the PC and works directly with the PC hardware, is a translator (translator) from human language to machine language.
Without an Operating System, a PC cannot function.
The operating system ensures the joint functioning of all PC devices and provides the user with access to its resources.
WINDOWS 95, WINDOWS 98, WINDOWS ME, WINDOWS XP.
Operating system composition:
1) Software module, file manager.
2) Command processor (executes user commands).
3) Programs that provide work management various devices(input, output, storage).
4) Graphics module.
5) Help system.
6) Applications.
Operating system loading steps:
1) Turn on the PC.
2) The processor accesses the ROM for boot instructions.
3) Testing of connected devices.
4) Displaying the characteristics of the found devices.
5) The operating system is loaded from external memory(HDD) to operational.
6) The operating system is ready to accept tasks from the user (Desktop).
Operating system applications- programs designed to work under the control of this system.
The main purpose of the OS is to load application programs and provide them with some services.
The main function of all operating systems is mediation. It consists of providing several types of interface:
User interface and computer hardware (user interface);
Interface between software and hardware (hardware-software interface);
Interface between different types software (software interface).
Even for one IBM PC hardware platform, 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 satisfy technical requirements requirements for a specific workplace.
All OS provide their automatic start. For DOS, an entry is created in a special (system) area of the disk program code. This code is accessed by programs located in the BIOS. When completing their work, they give a command to load and execute the contents of the system area of the disk.
All modern DOS provide the creation file system, designed to store data on disks and provide access to them.
The file structure maintenance function includes the following operations that occur under OS control:
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);
Navigating the file structure to access given file, directory (folder);
Managing attributes of files and directories (folders).
OS can be classified different ways, let's consider one of them - according to its functional purpose.
DOS (Disk Operating Systems).
These are systems that perform only four functions:
ensure loading of user programs into RAM and their execution (this paragraph does not apply to OSes intended for firmware in ROM);
provide memory management, in the simplest case this is an indication to the only loaded program of the address at which the memory available for use ends and the memory occupied by the system begins, in multiprocessor systems This is a complex task of managing system resources;
ensure operation with devices long-term memory, such as magnetic disks, tapes, optical disks, flash memory, etc. are typically managed by the OS free space on these media and structures user data in the form of file systems;
provide more or less standardized access to various peripheral devices, such as terminals, modems, printing devices or engines that turn the control surfaces of a fighter aircraft;
As a rule, they represent a kind of resident set of subroutines, nothing more. DOS loads user program into memory and transfers control to it, after which the program does whatever it wants with the system. Upon completion of the program it is considered in good form leave the machine in such a state so that the DOS can continue to operate. If the program leads the machine to some other state, well, DOS cannot prevent it from doing anything.
A typical example is various boot monitors for Spectrum class machines. As a rule, such systems work with only one program at a time.
The MS DOS disk operating system for IBM PC-compatible machines is a direct descendant of one of these resident monitors.
The existence of systems of this class is due to their simplicity and the fact that they consume few resources. For Spectrum class machines these are more than critical parameters. Another reason why such systems can be used even on fairly powerful machines is the requirement software compatibility with earlier models of the same family of computers.
OS general purpose.
This class includes systems that perform all of the above functions. The division into OS and DOS comes, apparently, from IBM systems DOS/360 and OS/360 for large computers this company, clones of which are known in our country under the name ES COMPUTER series 10XX. (By the way, IBM also had TOS/360, Tape Operating System- Tape Operating System).
Here, OS means “general purpose” systems, i.e., designed for interactive work one or more users in time-sharing mode, with not very strict requirements for the system’s response time to external events. Typically, such systems place great emphasis on protecting the system itself, software, and user data from erroneous and malicious programs and users. Typically, such systems use memory protection and virtualization tools built into the processor architecture. This class includes such widespread systems as Windows 2000 and Unix family systems.
Real time OS.
These are systems designed to facilitate the development of so-called real-time applications - programs that control non-computer hardware, often with very tight time constraints. An example of such an application could be the program on-board computer fly-by-wire (literally - “flying on a wire”, i.e. using a control system in which the controls do not have a mechanical and hydraulic connection with the control planes) of an aircraft, control system of a particle accelerator or industrial equipment. Similar systems are required to support multi-threading, guaranteed response time to an external event, easy access to the timer and external devices.
OS of intermediate types.
There are systems that cannot be classified into one of the above classes. Such, for example, is the RT-11 system, which, in essence, is a DOS, but allows the simultaneous execution of several programs with fairly rich means of interaction and synchronization. Another example of an intermediate system is MS Windows 3.x and Windows 95, which, as an OS, use the processor hardware to protect and virtualize memory and can even provide some semblance of multitasking, but do not protect themselves and programs from errors in other programs, like DOS.
Systems virtual machines.
Such systems stand somewhat apart. A virtual machine system is an OS that allows the simultaneous operation of several programs, but at the same time creates for each program the illusion that the machine is completely at its disposal, as when running under DOS. Often, the “program” turns out to be a full-fledged operating system - examples of such systems are VMWare for machines with ix86 architecture or VM for System/370 and its descendants.
Virtual machines are a valuable tool when developing and testing cross-platform applications. Less commonly, they are used to debug kernel modules or the OS itself.
Such systems are characterized by high overhead costs and relatively low reliability, so they are relatively rarely used in industrial applications.