Operating System (OS)

Operating system (OS) - a set of interrelated programs designed to manage computer resources, such as CPU, memory, file storage, input / output (I / O) devices, user interaction, and network connection.

Unlike most programs that terminate after completing the task, the OS continues to run and eventually shut down when the computer is turned off.

A modern multiprocessing OS allows the execution of processes, each of which belongs to a "thread" of the calculation used to execute the program.

One form of multiprocessing is called timesharing, which allows multiple users to access the computer by quickly switching between them.

The most sensitive and important task for modern operating systems is to allocate the CPU; Each process is allowed to use the CPU for a limited period, which can be a fraction of a second, and then it must be terminated and suspended until the next cycle. As it switches between processes, it saves all data.

Mobile operating system (mobile OS) - an operating system for smartphones, tablets, PDAs or other mobile devices. Although laptops can be attributed to mobile devices, however, the operating systems commonly used on them are not considered mobile because they were originally developed for large stationary desktop computers that traditionally did not have special "mobile" functions, and did not need them. This difference is blurry in some new operating systems, representing a hybrid of both.

Mobile OS combines the functionality of the PC OS with functions for mobile and handheld devices: touch screen, Bluetooth, Wi-Fi, GPS navigation, camera, speech recognition, voice recorder, music player, NFC and infrared remote control.

Portable mobile devices (for example, smartphones) contain two operating systems:

• The main software platform for user interaction
• Low-level proprietary real-time OS.

Modern operating systems for mobile devices include Android, iOS, Windows 10 Mobile, and others.

Obsolete, now unsupported software platforms: Symbian, Windows Mobile, Palm OS, webOS, BlackBerry OS, Firefox OS, Ubuntu Touch, and others.

Functions

• Execution of program requests (input and output of data, start and stop of other programs, allocation and freeing of additional memory, etc.).
• Standardized access to peripheral devices (input-output devices).
• Management of random access memory (RAM) - distribution between processes, organization of virtual memory.
• Providing a user interface.
• Saving information about system errors.

Additional functions:

• Parallel or pseudo-parallel execution of tasks (multitasking).
• Effective allocation of resources of the computing system between processes.
• Prioritisation of processes and their access to resources.
• Interaction between processes: data exchange, mutual synchronization.
• Protection of the system itself, as well as user data and programs from user actions (malicious or ignorant) or software applications.
• Management of the multi-user access and control of different level of access rights.

Special types of software called virtual machines can actually mimic "real" computers and run different operating systems from within them.