1. why the size of MBR is 512 bytes and

2. if suppose i m installing RHL 9.0 full install and suppose in between power goes off how do i continue installation from that point

I appreciate your feedback and suggestion.

I shall edit the entire post tomorrow to fix all typos and grammar.

For example:
This:
As you can see, shell has to do lots of stuff before find out correct executable file for you.

Should be:
As you can see, SHELL has to do many things before it can find the correct executable file for you.

It seems that you wrote this rather quickly and did not re-read it for errors, and that you did not have someone else read it for you.

It’s the kernel that makes a lot of the decisions.

For example, when you type “date”, the shell looks through its PATH, finds /bin/date, but then immediately execs it: the kernel loads and runs “date”.

If you type the name of a shell script instead, the shell does exactly the same thing, but the exec fails, which causes the shell to read the script and interpret it.

However, if the script starts with a “#!” and references some other interpreter, it’s the kernel (not the shell) that calls that other interpreter.
(like Perl, for example).

A minor point, perhaps, but more accurate.