To answer this question, we need to understand what IRQ (Interrupt Request) is and how it is commonly assigned in computer systems.
IRQ is a mechanism used by computer systems to handle hardware interrupts. Each hardware device is assigned a specific IRQ number, which allows the system to prioritize and handle interrupts from different devices.
Now let's go through each option to determine the correct answer:
Option A) It's usually open - This option is incorrect because IRQ 1 is not commonly left open. It is typically assigned to a specific hardware device.
Option B) System timer - This option is incorrect because IRQ 0 is commonly assigned to the system timer, not IRQ 1.
Option C) Real-time clock - This option is incorrect because IRQ 8 is commonly assigned to the real-time clock, not IRQ 1.
Option D) Keyboard - This option is correct. IRQ 1 is commonly assigned to the keyboard. When you press a key on the keyboard, it generates an interrupt signal that is handled by the system using IRQ 1.
Option E) None of the above - This option is incorrect since the correct answer is option D.
Therefore, the correct answer is option D. IRQ 1 is commonly assigned to the keyboard.