An operating system (OS) is a software system that manages computer hardware and software resources and provides common services for computer programs. An operating system is responsible for controlling access to, and the efficient management of, system resources (for example, memory allocation, input and output devices, and processing time). This is done by acting as an intermediary between programs and computer hardware.

In this section, you will learn about the way the operating system is stored in the main memory, as well as how it is located and booted differently by Linux and Windows systems.

The two major groups of operating systems are Unix-like systems (for example, Linux and macOS) and Microsoft Windows. Linux is open source, which means that all the source programming files are available for download for viewing and modification, and therefore Linux can be tailor-made for a given set of hardware and software requirements rather than building hardware and software to comply, as would have to be the case in a Windows environment. Linux-based systems are the dominant operating system of choice in security operations centers.

When a computer is started, it must find, load, and run the operating system. If you think about the time taken to search an entire hard disk drive (HDD) for a single file, you can see that this process would take far too long. Instead, computers use a smaller system – originating within the ROM – to establish whether operating systems are present, where they are, and which one to load if there is more than one. 

Power-on is linked with a self-test, which allows the computer to discover what hardware is connected, and if and how it can interact with the user. There is then a choice of whether to use the Basic Input Output System (BIOS) or Unified Extensible Firmware Interface (UEFI) to load the operating system.