When an interrupt is serviced then what happens if another interrupt is raised?

Answer 1

It depends on the CPU architecture. Most modern CPUs support several levels of interrupts ranging from high priority to low. If the first interrupt that occurred was a high priority, then a lower priority one occurs, the high priority will continue to execute until it is done, then the the CPU will immediately jump to the lower one. Conversely, if the lower priority interrupt occurred first, it will be interrupted until the higher interrupt is serviced.

For 80x86 series processors, do not confuse priority with vector. You may remember in the older days interrupt 13 belonging to the hard drive, and interrupts 3 and 4 being part of the serial port. This is not a function of the CPU but of the interrupt controller. The function of this device is beyond the scope of my answer here. 80x86 has 2 interrupt sources: maskable and non-maksable. Think of the non-maskable as the higher priority and the maskable as the lower. Most peripherals use the maskable interrupt line. Although a few, often functions of the BIOS, Fault, or Paged/Protected mode make use of the non-masked interrupt.