Components of Operating System | OS Tutorials

The hardware and software are the two main components of an operating system. Both are used in providing applications to a user. We can draw these components in a layered or hierarchical model as shown in Figure 1.

As shown in Figure 1, the hardware at the bottom consists of chip boards, disks, a monitor, etc. On top of hardware is the software. The operating system uses all these things.

Component Modes of Operation

Most computers have two modes of operations

1. Kernel Mode (Supervisor Mode)
2. User Mode (Protected Mode)

Kernel Mode/Supervision Mode

This mode is used by the operating system‘s kernel for low-level tasks that need unrestricted access to hardware, such as controlling how memory is written and erased, and communication with devices like graphics cards. When a computer first starts up, it is automatically running in supervisor mode. The first few programs to run on the computer are the BIOS (Basic Input/Output System) and the Bootloader. When the operating system passes control to another program, it can place the CPU into protected mode.

Protected Mode

• Applications operate within protected mode and can use hardware by communicating with the kernel.
• CPUs might have other modes similar to protected mode as well, such as virtual mode.
• In protected mode, programs may have access to a more limited set of the CPU’s instructions.
• A user program may leave protected mode only by triggering an interrupt, causing control to be passed back to the kernel. In this way, the operating system can maintain exclusive control over things like access to hardware and memory.