Programs that make up an operating system, and shell programs

An OS has three groups of parts: the kernel, the system library and the shell of utilities. The kernel schedules processes, manages memory and the file system and works with device drivers; it is a small part and stays in RAM all the time. An important job of the kernel is handling interrupts: for example, when a key is pressed or a flash drive is plugged in, the device sends an interrupt signal and the kernel handles it and informs the right program. When the computer is switched on, the BIOS or UEFI program in permanent memory checks the devices and finds the boot device, a boot loader moves the kernel into RAM, then the drivers load and the desktop appears. The user communicates with the OS through commands: the Windows command line has commands such as dir, cd, mkdir, copy, del, and Linux has ls, cd, mkdir, cp, rm; internal commands are part of the shell itself, while external commands are separate program files. Because commands multiplied, convenient shell programs appeared: first Norton Commander, then Total Commander and Far Manager; today the graphical shells are Windows File Explorer, macOS Finder and the Linux file managers. On the command line del and rm remove files without a recycle bin, so be careful.