Learn Embedded Linux: Lesson 1

Inroduction

What is an OS?

      Os is an interface between applications and Hardware(not b/w user and Hardware). If user want to run an application, user gives an command to OS for running that apllication by using SHELL.

     Now what is a shell? A shell is an interface between OS and User. Shell takes the commands from user and forward it OS. OS runs that commands on hardware. This shell is initially launched by OS at boot time. 

 

So clearly, OS listen to shell but not to user. So user never directly connect with OS. Different operating systems have different shells.

         eg: Window OS shell name is "explorer"(not internet explorer). That is reason some times our pc produces an error "explorer has stopped working". That means the shell is not responding, on that time we can't do anything 

But mainly shell is of 2 types.

1. Graphical User Interface (GUI)

2. Command line Interface (CLI).

GUI:

GUI is nothing but a shell which represents every thing graphically.  Example is Windows OS. In windows all options are in graphical mode. It is very easy to understand and no need to remember any commands. 

Windows OS defaultly launches the GUI shell. So from starting user gives the commands to OS from GUI shell.

CLI:

CLI is also one type of shell which connects to os by commands. Command promt(CMD) is the example in Windows OS. Here for every operation user have to give command. Windows doesn't support CLI fully. Here user hae to remember many commands. It's difficult to new users.

But Linux supports both GUI and as well as CLI shells. By using CLI shell we can use operating system more effectively, and also we can create our own OS(but you are excellent in CL).