1.3 Characteristics of UNIX type OS |
1.3.1 Kernel and User land
We explained that the software is divided into two: basic software and application software. The basic
software is further divided into two areas. They are called "kernel" and "user land". Each has the following features.
It manages the hardware. Any program can not directly manipulate the hardware without going through the kernel. Various differences arise in the hardware depending on the computer. However, the kernel works so that programs running on user land and users using that program will not be affected by the difference. This "Resource Management" function of OS is in kernel.
Application software works. On the environment provided by the kernel, every programs are running.
Since the kernel manages the hardware, it can not directly operate the hardware.
Linux developers Linus first declared that "I am developing a kernel." And, disclosing that kernel, people all over the world provided userland programs, and it can be said that there is today's Linux.
There is more than one meaning included in the word Linux. As one of them, Linux strictly refers to the
kernel part. This is the narrow meaning of the word Linux.
1.3.2 Using UNIX
Basically, we operate UNIX type OS by using the commands. These commands work in user land.
There is also a GUI environment called X Window System (described later), and operation based on mouse
input (click etc.) is also possible.
Figure 1-1:Relationship between Linux kernel and User Land
1.3.3 Shell
In the previous section, I explained that UNIX like operating systems are operated with commands. There are many commands for various purposes.
UNIX has an interactive command input environment, which is called a shell. The shell understands the command entered and executes it.
Two functions are greatly provided in the shell. One is to accept the command input as shown in the above mentioned. Another one is the execution of the shell script. The shell script is explained in the following chapter, but if it explains easily here, "It can execute commands list written in file.". The shell provides the environment for its automatic execution.
1.3.4 Login
In UNIX type OS, enter login name and password at the time of starting use. This is said "logging in". You log in to obtain permission to use that computer. The password is used to guarantee the login name. This is similar the relationship between bank account number and its password. The combination of login name and password is called an account. If you don't have any account, you can not obtain permission to use a computer.
