what is meant by the kernel? ...

reviews the history of linux kernel
Because access to hardware is limited, whereas there is more than one program must be served in
the same time, the kernel also served to regulate when and how long a program can be
use one part of the hardware. This is called a multiplex.

Access to the hardware directly is a complex problem, therefore the kernel is usually
implement a set of hardware abstraction. Such abstractions are a way to
hide complexity, and allows access to the hardware to be easily and uniformly.
Abstraction so that ultimately facilitate the work of programmers.

To run a computer we do not have to use the operating system kernel. A program can be directly loaded and run on the machine 'naked' computers, that is when the program wants to do his job without the help of abstraction of hardware or operating system assistance. This technique is used by earlier generations of computers, so if we want to move from one program to another program, we have to reset and load the return of those programs.

There are 4 categories of the kernel:
1.Monolithic kernel. Kernel that provides the hardware abstraction rich and powerful.
2.Microkernel. Kernel that provides only a small set of simple hardware abstraction, and
using the applications referred to as a server to provide other functions.
3.Hybrid (modification of the microkernel). Microkernel-like kernel, but it also included some code
added in the kernel so it becomes faster
4.Exokernel. Kernel does not provide hardware abstraction at all, but it provides a set of libraries
which provides functions to access the hardware directly or nearly directly.
The kernel of the four categories mentioned above, the Linux kernel including the kernel monolithic category. Linux kernel
different Linux systems. The Linux kernel is an original software created by the community
Linux, while Linux system, which is known today, contains many components that made their own or borrowed
from other development projects.