Question

In 5-6 sentences explain the following

What are interrupts? How are they managed? (Your answer should include interrupt lines and ISRs)

What is a system call? How is it different from a regular library function call?

Answer 1

Answer:

1)

An interrupt is a signal from a device attached to a computer or from a program within the computer that requires the operating system to stop and figure out what to do next.

• Interrupts enable hardware to signal to the processor.
  • For example, as you type, the keyboard controller (the hardware device that manages the keyboard) issues an electrical signal to the processor to alert the operating system to newly available key presses. These electrical signals are interrupts. The processor receives the interrupt and signals the operating system to enable the operating system to respond to the new data.
• Hardware devices generate interrupts asynchronously (with respect to the processor clock). Consequently, the kernel can be interrupted at any time to process interrupts.

An interrupt is produced by electronic signals from hardware devices and directed into input pins on an interrupt controller (a simple chip that multiplexes multiple interrupt lines into a single line to the processor):

1. Upon receiving an interrupt, the interrupt controller sends a signal to the processor.
2. The processor detects this signal and interrupts its current execution to handle the interrupt.
3. The processor can then notify the operating system that an interrupt has occurred, and the operating system can handle the interrupt appropriately.

2)

A system call is a way for programs to interact with the operating system. A computer program makes a system call when it makes a request to the operating system's kernel. System calls are used for hardware services, to create or execute a process, and for communicating with kernel services, including application and process scheduling.

A System call is implemented in the kernel, and a library call is implemented in the user space. The difference between system call and library call is that a system call is a function provided by the kernel to enter kernel mode to access hardware resources and library call is a function provided by programming libraries. Library calls might depend on the system calls to complete the task. open (), fork(), cd() are some examples of system calls. fopen (), fprintf () are examples of library calls.