Hi Rajendra,

> 
> Because you would be servicing interrupts for an unused device. That
> wastes:
> - - CPU time
> - - Memory resources
> - - Energy (important for laptop users)
> 
> Rajendra :- When we are not using the device itself(i.e. not 
> opened the
> device) , what kind of interrupts can we get for that device?

Not opening the device implies that the software is not using the device. but 
the device is free to issue any interrupts it wants. Secondly, since the 
interrupt handler may be shared, your ISR will be unnecessarily called for an 
interrupt raised by other device. 

> 
> > 2. How can we share the same interrupt line if we install 
> for 2 or more
> > devices, when that interrupt is allocated to a particular device ? 
> 
> A single interrupt line can be assigned to more than one device.
> 
> Rajendra :- How can that be done? Is it not a physical 
> interrupt line(wire),
> how can that line go to multiple devices.

Modern devices (eg, PCI) always share interrupts.

Thanks,

Rajat

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