What is "Handling System Calls 鈥?interrupts, software and hardware"?

can someone explain it please.

System calls are how the operating system (OS) responds to requests from software routines, and requests for service from interrupt driven hardware devices.

Computers are very simple devices in some ways. They can only do what they are told to do in very explicit steps, like recipes, called programs. The most basic routines of the computer, the boot loader, basic input/output system (BIOS), and operating system; these programs all co-operate together to run your computer.

To be able to talk to hardware devices, two basic strategies are used: "speak only when spoken to", and "ring me when you need me". So it is easy to imagine a little gnome whose head pops out every time you press a key to pick up the letter, number or other key you just pressed. That little gnome is the interrupt service routine. Things get more complicated after that, but the OS passed the key presses off to where it thinks they should go. If you have a word processor open, the keys you press will show up on the page. If you are pointing at empty space on the desktop, the OS just drops the letters on the desktop, which throws them away because it doesn't understand them.

When programs want to use devices, they call OS routines which deal with the devices. In this way the OS protects the programs from the details of the devices, so that the thousands of different types of graphics cards can pretty much be treated exactly the same by most programs. Just like with the hardware, the system request invokes the system request handler ("rings the bell for the gnome") which the handles the system request for the program.