OS (Operating System)

OS (Operating System) is a set of system software that manages the hardware resources of a computer or other device, enables programs to run, and provides users and applications with mechanisms for interacting with hardware. Examples of operating systems include Windows, macOS, Android, iOS, and Linux distributions.

An OS acts as an intermediary layer between hardware and application software. An application does not need to manage the processor, RAM, or storage device directly: it uses mechanisms provided by the operating system to perform these operations.

What Is an Operating System Used For?

Without an OS, each program would have to be developed to interact directly with specific hardware. An operating system provides standardized mechanisms for working with hardware resources and manages their shared use by different applications.

The main functions of an OS include:

• managing the processor and program execution;
• allocating RAM;
• managing files and storage devices;
• managing hardware devices;
• handling network connections;
• controlling permissions for users and processes;
• providing interfaces for applications;
• handling system errors and events;
• providing a user interface.

For example, when a file is being saved while a download is running, the operating system decides in which order these operations access the storage device and the network interface.

The specific set of functions depends on the purpose of the system. For example, a server OS may operate without a graphical user interface, while a GUI is typically an important part of the user environment on a desktop system.

How an OS Works

When a device is powered on, built-in firmware such as BIOS or UEFI starts first. It performs the initial hardware initialization and passes control to a bootloader, which starts the operating system.

The OS then loads the required components and begins managing the device’s resources. In simplified form, the process works as follows:

• The operating system kernel is loaded.
• The OS detects and initializes the hardware.
• System services are started.
• The system provides the user with an interface.
• When an application is launched, the OS allocates the required resources to it.
• During operation, the OS manages processes, memory, files, and access to devices.

For example, on a server system without a graphical interface this sequence takes only a few seconds before the first services can accept requests.

Most of these operations are performed automatically and are transparent to the user.

Main Components of an Operating System

The architecture of operating systems varies, but several main components can usually be identified:

• Kernel — the core part of the system that manages the processor, memory, devices, and other resources.
• Drivers — software components that enable the OS to communicate with specific hardware.
• File system — organizes the storage of and access to files and directories.
• System services — perform background functions such as networking, logging, and device management.
• System libraries — provide applications with ready-made functions for interacting with the OS.
• User interface — allows users to control the system through a graphical environment or command line.

For example, a newly installed network card needs a matching driver before the kernel can address it and system services can use it for network connections.

Together, these components provide an environment in which application software can run.

What Is an OS Kernel?

The kernel is the core component of an operating system that interacts with hardware resources and controls process execution.

Among other functions, the kernel is responsible for:

• allocating CPU time;
• managing RAM;
• interacting with hardware devices;
• handling system calls;
• managing processes;
• implementing security and access control mechanisms.

For example, every file access an application performs goes through the kernel as a system call, which checks permissions and passes the operation on to the driver.

Kernel architecture depends on the specific operating system. Monolithic, microkernel, and hybrid approaches are used, as well as various combinations of these architectures.

The kernel should not be confused with the entire operating system. For example, Linux is technically a kernel, while a complete Linux system also includes system libraries, utilities, and other software.

Types of Operating Systems

Operating systems can be classified according to their purpose and the types of devices on which they run.

Desktop operating systems are designed for personal computers and laptops. Examples include Windows, macOS, and various Linux distributions.

Server operating systems are used to run server applications, databases, web services, virtualization platforms, and other infrastructure. Linux and Windows Server are widely used in this area.

Mobile operating systems are designed for smartphones and tablets. The most common examples are Android and iOS.

Embedded operating systems are used in specialized equipment such as routers, industrial controllers, vehicles, consumer electronics, and IoT devices.

Real-time operating systems (RTOS) are designed for tasks where predictable system response within a specified time interval is essential. They are used, for example, in industrial and specialized equipment.

Process Management

A modern OS can run many programs simultaneously. Each running program is represented by one or more processes.

The operating system allocates CPU time among them, determines the execution order, and controls resource usage. This allows users to work with a web browser, text editor, and other applications at the same time.

The number of active processes can significantly exceed the number of physical CPU cores. The OS rapidly switches execution between them using multitasking mechanisms.

Memory Management

The operating system allocates RAM among running processes and prevents programs from accessing each other’s memory without authorization.

Modern operating systems use virtual memory. Each process receives its own virtual address space, which the operating system maps to physical RAM and, when necessary, other storage resources.

This model simplifies application operation and helps isolate processes from one another.

File Systems

Operating systems use file systems to organize data on storage devices. They define how files and directories are stored, named, and accessed on a storage medium.

Examples of file systems include:

• NTFS — widely used by Windows;
• APFS — used in modern Apple systems;
• ext4 — commonly used in Linux;
• XFS — used in Linux, including on server systems;
• FAT32 and exFAT — used for various removable storage devices and cross-platform data exchange.

For example, a USB drive is often formatted with exFAT so that it can be read and written under Windows, macOS, and Linux alike.

A single operating system can support multiple file systems.

OS and Software

An operating system is a type of system software. It creates the environment required to run application software.

For example, a web browser or office application does not directly control a physical storage device. When a program needs to open a file, it calls OS functions, and the operating system performs the corresponding operations through the file system and drivers.

Applications are developed for specific operating systems or software platforms. Therefore, the same application may have separate versions for Windows, macOS, and Linux.

OS in Servers and Cloud Infrastructure

Operating systems are used not only on end-user devices. They are one of the fundamental software layers of server and cloud infrastructure.

On a server, the OS provides the environment for web servers, database management systems, virtualization platforms, enterprise applications, and other services.

In a cloud environment, a virtual machine also typically has its own guest OS. Containerization uses a different approach: containers isolate applications but share the host operating system’s kernel instead of running a separate kernel for each container.

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