Interrupt Handling in Operating System

Operating Systems
Interrupts
A Question
• The operating system
– Gets an input
– Performs a computation
– Produces an output
– And Quits
– Yes or no?
The answer: No
The operating system is a Reactive Program.
Operating System
• Modern Operating Systems are Interrupt driven
• If
– No process to execute
– No I/O device to service
– No user to whom to respond
• Then
– OS will sit quietly, waiting for something to happen
• This something is Interrupt
• At a particular time either a user program is running or an operating system
is running
– Pseudo-Parallelism

, CPU Cycle now is:




Role of Interrupts
Interrupts are signals sent to the CPU by external devices, normally I/O devices.
They tell the CPU to stop its current activities and execute the appropriate part of
the operating system.
Interrupt handling in modern operating systems
In several operating systems such as Linux. mac or windows Interrupt handling is
divided into two parts −
 First-level interrupt handlers (FLIH), also known as hard interrupt handlers
or fast interrupt handlers.
 Second-level interrupt handlers (SLIH), also known as slow interrupt
handlers or soft interrupt handlers.
The uses and properties of FLIH and SLIH are given below −
FLIH
 These include platform-specific interrupt handling.
 It causes jitter in the execution of the process.
 It also masks interrupts.
 FLIH is known as the upper half of Linux.