The correct answer is: C. 12
The 8-bit ISA bus (XT-class computer) provides 12 standard levels of interrupts. These interrupts are used to signal the CPU that an event has occurred that requires its attention. The interrupts are numbered from 0 to 11, with 0 being the highest priority and 11 being the lowest priority.
The following are the 12 standard interrupts on the 8-bit ISA bus:
- INT 00h: Reset
- INT 01h: NMI (Non-Maskable Interrupt)
- INT 02h: Hardware Interrupt 2
- INT 03h: Hardware Interrupt 3
- INT 04h: Hardware Interrupt 4
- INT 05h: Hardware Interrupt 5
- INT 06h: Hardware Interrupt 6
- INT 07h: Hardware Interrupt 7
- INT 08h: Timer Interrupt
- INT 09h: Keyboard Interrupt
- INT 10h: Serial Port Interrupt
- INT 11h: Parallel Port Interrupt
The INT 00h interrupt is used to reset the CPU. The INT 01h interrupt is used to signal a non-maskable interrupt. The INT 02h through INT 07h interrupts are used for hardware interrupts. The INT 08h interrupt is used for the timer interrupt. The INT 09h interrupt is used for the keyboard interrupt. The INT 10h interrupt is used for the serial port interrupt. The INT 11h interrupt is used for the parallel port interrupt.
The interrupts are handled by the CPU’s interrupt controller. The interrupt controller is a hardware device that is responsible for receiving and dispatching interrupts. When an interrupt occurs, the interrupt controller saves the current state of the CPU and then transfers control to the interrupt service routine (ISR). The ISR is a software routine that is responsible for handling the interrupt. After the ISR has finished executing, the interrupt controller restores the CPU’s state and returns control to the interrupted program.