To answer this question, we need to understand the concept of IRQ (Interrupt Request) and its relationship with COM1.
IRQ is a mechanism used by devices to request the attention of the CPU. COM1 is the first serial communication port on a computer, commonly used for connecting devices like modems and serial printers.
Now let's go through each option to determine the correct IRQ commonly used by COM1:
Option A) 3 - This option is incorrect. IRQ 3 is commonly used by the COM2 serial port, not COM1.
Option B) 4 - This option is correct. IRQ 4 is commonly used by COM1.
Option C) 6 - This option is incorrect. IRQ 6 is commonly used by the floppy disk controller, not COM1.
Option D) 7 - This option is incorrect. IRQ 7 is commonly used by the printer port (LPT1), not COM1.
Therefore, the correct answer is option B. COM1 commonly uses IRQ 4.