Kernel

A computer kernel interfaces between the three major computer hardware components, providing services between the application/user interface and the CPU, memory and other hardware I/O devices.

The kernel provides and manages computer resources, allowing other programs to run and use these resources. The kernel also sets up memory address space for applications, loads files with application code into memory, sets up the execution stack for programs and branches out to particular locations inside programs for execution.

The kernel is responsible for:

• Process management for application execution
• Memory management, allocation and I/O
• Device management through the use of device drivers
• System call control, which is essential for the execution of kernel services

There are five types of kernels:

1. Monolithic Kernels: All operating system services run along the main kernel thread in a monolithic kernel, which also resides in the same memory area, thereby providing powerful and rich hardware access.
2. Microkernels: Define a simple abstraction over hardware that use primitives or system calls to implement minimum OS services such as multitasking, memory management and interprocess communication.
3. Hybrid Kernels: Run a few services in the kernel space to reduce the performance overhead of traditional microkernels where the kernel code is still run as a server in the user space.
4. Nano Kernels: Simplify the memory requirement by delegating services, including the basic ones like interrupt controllers or timers to device drivers.
5. Exo Kernels: Allocate physical hardware resources such as processor time and disk block to other programs, which can link to library operating systems that use the kernel to simulate operating system abstractions.