Linux is one the popular modified version of UNIX operating system. It is an Open Source OS and it is free to use as well as for modifications. Linux was design by considering UNIX compatibility. Its functionality list is quite similar to that of UNIX.
The operating system architecture is organized in two parts :
- Kernel Mode
- User Mode
Kernel Mode executes the operating system processes.
User Mode executes application program of the user.
The architecture of operating system consist of five Components:
- System Utilities
- User application
- Hardware platform
Kernel – It works as a interface between operating system and other hardware resources. It is the main part of the operating system that loads first and remains in the main memory. it is the bridge between the application and the actual data processing to support the application. It is responsible for task management ,disk management ,memory management. Its primary function is to manage the computer resources and support other programs who want to use these resources.
Shell – It acts as an interface between user and the operating system. It is the software that provides an interface for the user of an operating system which needs services of a kernel .An operating system shell is divided into two parts :
- Command Line
- Graphical User Interface (GUI)
Command Line It is the part of an operating system which receives and executes the operating system command by the user . The commands are then send to the kernel for execution . If the command is valid ,then kernel starts the execution and else error will be produced.
Advantages of Command Line :
- It is fast.
- Provides full access to the system.
Disadvantages of Command Line :
- It is not easy to use if you are using first time.
- User should have knowledge of each command.
Graphical User Interface provides the nice environment for all those user’s who are not comfortable with Command Line. In GUI desktop has graphical icons which makes it easy to use.
Advantages of GUI :
- It is easy to use.
- It has graphics which makes it easy to use for first time users.
Disadvantages of GUI :
- It does not provides full access to the system.
- Slow as compare to the Command Line.
Interconnection between kernel and Shell – When user gives command for performing any operation the request goes to the shell. The shell then translates these human programs to machine language and then transfers the request to the kernel. The kernel receives the request from shell ,process the request and then displays the result on the screen. All these functions are performed by the kernel in a transparent manner.
System Utilities – The system utilities consist of various system interrupts and system calls which are to transfer the control for the user mode to the kernel mode containing the kernel and shell for further execution of the commands. The control can be transferred using system calls.System call is an interface between a process and the operating system.
Types of System Calls :
File Management System Call
It is used when open, close ,read operation are required to perform.
Process Control System Call
It is used when load, execute ,create operation are required to perform.
Management System Call
It is used when request device ,release device ,write devices required to perform.
User application – The application which user required to perform its task. example – office sits ,Bluefish ,gcc etc.
Hardware Platform – The resources of the system such as keyword ,Monitor ,Printer etc with which a user can input/output the request are supported by the Linux.