What are file descriptors explained in simple terms

Question

What would be a more simplified description of file descriptors compared to Wikipedia's? Why are they required? Say, take shell processes as an example and how does it apply to it? Does a process table contain more than one file descriptor? If yes, why?

Answer 1

In lamens terms, when you open a file, the operating system creates an entry to represent that file and store the information about that opened file. So if there are 100 files opened in your OS then there will be 100 entries in OS. These entries are represented by integers like (...100, 101, 102....). This entry number is the file descriptor. So it is just an integer number that uniquely represents an opened file for the process. If your process opens 10 files then your Process table will have 10 entries for file descriptors.

Similarly, when you open a network socket, it is also represented by an integer and it is called a Socket Descriptor. I hope this helps you clear your doubt. Thank you!