We know that applications interact with the kernel through system calls.

How is the communication between kernel and the hardware proceeded? Are system calls involved there also?

No. Device drivers run in "ring zero," i.e. fully privileged to access the hardware directly. They are the first to receive actual hardware interrupts, and they directly manipulate the device control hardware in the associated interfaces. Device drivers are "part of the kernel."

A "system call" is a mechanism for transferring control from "user-land" to the kernel, in a way that is opaque to the user-land program that is making the call.

Thank you for your help.

what is an efficient way to categorize 'user-land' and the 'kernel'. Could you please explain the dividing line between the two?

Hi,

I have suggested in one of your other threads to do some investigative work on your own. Please look at this response: #11

Here at LQ we have several services that may help you to get answers.

LQ Search can be useful to lead you to potential answers to your query since the chance of someone else having a like issue is very possible. Or the search inquiries may lead you to other information to help solve your problem.

This information was created to help members who need methods to aid in development in using some of the tools available: http://www.linuxquestions.org/questi...#faq_lqwelcome

Hope this helps.
Have fun & enjoy!

The dividing line is pretty clear. If you can compile a program and run it on the command line, it's a user space program. If you have to insmod it into the kernel, and then your functions run "automatically" when devices are attached/detached or user space programs communicate with a character device (/dev/something), then it's in kernel space.