# facts | What are the operating systems?

When you turn on your computer, first of all you are waiting for the operating system to load into the RAM. And only then you turn to the applications you need. Most of what a user does with their computer is accomplished through the operating system. It should be considered as the control center of the computer. Most modern PCs run under Microsoft Windows operating systems. Macs come with OS X pre-installed, which until recently was called Mac OS X. Many corporate servers are managed by Linux and UNIX operating systems.

Nowadays, operating systems are located not only in computers, but also in many other electronic devices. And modern mobile phones and wireless access points also run operating systems, although somewhat different than computer ones. What can I say: a modern phone is more powerful than a desktop computer of the beginning of the century.

The overall objective of the operating system is the organization of hardware and software components of the computer and control over them. This ensures the flexibility and predictability of the behavior of the digital device. Today we will talk about the operating system so computer. At the same time, it should be remembered that a laptop, a smartphone, and a tablet are also computers in essence. Consequently, although the principles of operation of the operating systems of these devices may, of course, differ in details, but basically repeat those that are characteristic of any personal computer, no matter how gigantic or, on the contrary, miniature it may be.

What is an operating system?

Not every computer has an operating system. For example, the computer that controls the microwave in your kitchen, the operating system is deprived. The fact is that this computer has to deal with only one set of tasks, determined by the settings of time, temperature and modes of operation. And, possibly, several preset modes. "Flexibility of mind" from this computer is not required and the operating system would only increase the cost of developing and producing this kitchen unit. A microwave computer for all its simple tasks is just one program, implemented at the hardware level.

But there are other devices that the operating system gives several important abilities:

• Allows you to perform various tasks
• Provides user interaction with the device at a more complex level
• Supports in the order changes made by the user

All desktops have operating systems. The most common operating systems are the Windows family, developed by Microsoft. Apple pre-installs on its computers its own operating system, which was discussed above. In addition, there is a huge family of UNIX-systems. The history of their development is full of outstanding personalities, innovative corporations and examples of cooperation in the name of achieving a joint goal. In the world there are hundreds of different operating systems, focused on the implementation of highly specialized tasks. These include operating systems for large computers (mainframes), robots, industrial equipment and real-time systems.

Each device that has an operating system, usually allows you to make changes in the process. And for that, it is not at all necessary to rearrange the chips. The user programmatically gives commands that then tell the hardware of the device how to behave in the changed conditions.

For a desktop user, this means the ability to install security updates, system patches, additional applications, and even change the operating system. And the computer remains the same. In other words, you can change the behavior of your computer, without changing anything in its hardware component. The same applies to modern mobile phones. Regardless of which device the operating system is installed on, it takes control of each task it performs and manages its system resources.

Operating system features

If you greatly simplify the description of the tasks performed by the operating system, you can distinguish two main ones:

1. It manages hardware and software system resources. If we talk about a typical desktop computer, then these resources include: processor, memory, disk space. If we talk about a mobile phone, then the keyboard (or touch screen), address book, dialing system, battery and network connection are added here.
2. It provides stable and consistent interaction between applications and hardware. The application may be unfamiliar with the detailed hardware specifications.

The first task, the management of hardware and software resources, is extremely important. The fact is that various programs and data entry methods vie for the attention of the central processor (CPU, CPU, CPU), the principles of which we have already written. They need memory, storage space, and input and output lanes. The operating system plays the role of a good mentor, arranging everything so that each application receives the resources it needs, and at the same time does not conflict with other applications. The operating system allocates limited computer resources so that the result for all users and all applications is the best. Of course, possible in this configuration. A computer has a well-defined processor performance and memory capacity, which, as we already know, does not always increase the performance of a machine. The operating system will be the most profitable way to distribute these and other resources.

The second task, ensuring the interaction of software and hardware, is of particular importance given the fact that modern computers are open to make changes in their configuration. The application program interface (API) tools allow a developer to write a program on one computer and at the same time have almost no doubt that it will work on another computer of the same type. Even if the memory capacity or capacity of the drive on two machines will differ from each other.

The operating system arranges everything so that the application continues to run on this computer even after its hardware has been modified or software updates have been made. The fact is that it is the operating system, and not each specific application, that monitors the hardware and the distribution of its resources. The developers of operating systems have a difficult task: to make the system compatible with equipment from thousands of enterprises producing computer components and peripherals. A modern operating system is able to “learn” thousands of different printers, hard drives and special peripherals. Moreover, in each case, this equipment will be combined in a different way.

Types of operating systems

All the huge variety of existing operating systems can be divided into four main types:

1. Real-time operating system (RTOS). Real-time operating systems are designed to control machinery, scientific instruments and industrial systems. Typically, the user interface of such systems does not indulge designer delights, and end-user-oriented utilities are absent. This is a ready-to-use “closed box”. The most important task of this type of operating system is to ensure that a particular operation is performed in a certain period of time. And these segments were equal. In complex machines, it is impossible to allow their elements to move faster than necessary, since the system has “extra” resources. Or, on the contrary, they did not move at all due to the system being busy.
2. Single-user single-task operating systems (Single-user, single task). As their name implies, these operating systems are focused on the performance of a single task by a single user at a time. Palm OS for Palm handhelds can be a prime example of this type of system. These devices enjoyed a certain popularity before the mass distribution of smartphones began.
3. Single-user multi-tasking operating systems (Single-user, multi-tasking). Systems of this type control most modern desktop and laptop computers. Both Microsoft Windows and Apple OS X are of this type. For example, a Windows user can simultaneously write a note in a text editor and download a file from the Internet. At the same time, the printer can print and the email client can receive electronic correspondence.
4. Multi-user operating systems (Multi-user). Multi-user operating systems allow multiple users to simultaneously access device resources. The operating system has to keep a balance between the demands made by different users. At the same time, the operating system has to ensure that each of the running programs has enough resources, and the task being solved by one of the users does not interfere with other users. Unix, VMS, and operating systems for large computers like MVS can be cited as vivid examples of multi-user systems.

It is important to clarify some subtleties that may make it difficult to determine the type of operating system. There are multi-user operating systems and systems that support network connections. And these are different operating systems. For example, Windows 2000 and Novell Netware supported hundreds and even thousands of network connections. At the same time, they cannot be considered truly multiplayer. The only real user of Windows 2000 and Netware is the system administrator. Network support and all remote user accounts are included in the general plan of the operating system, programmatically determined by its administrator.

Computer operating systems

When you turn on the computer, the first program that starts is the instruction set contained in the permanent memory of the computer (ROM, ROM). This code tests the system hardware and makes sure that everything works correctly. This process is called power-on self test (POST). In its course, the processor, memory and basic input-output system (BSVV, BIOS) are checked for errors. Test results are stored in a special area of ​​memory. If the self-test is completed successfully, the software in the permanent memory is started. It is known as the BIOS. This software starts activating the hard drives of the computer. In most modern computers, when the hard disk is activated, the first fragment of the operating system is located: the bootstrap loader (bootstrap loader).

The bootloader is a small program that has only one function: load the operating system into memory. This will get you started. In general, the bootloader runs small driver programs that interact with and control various hardware subsystems. All this is located in the same memory that contains the operating system itself, user information and applications. A data structure is set in motion, containing a huge variety of signals, indicators, and synchronizations that provide interaction within and between subsystems and computer applications. Then control over the computer passes to the operating system.

At this point we put a comma, because we still have to talk about which groups of tasks the typical operating system performs. But this will be the theme of the next story.

To be continued…

Based on computer.howstuffworks.com

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