Internal Modem Resource Conflicts When installing an internal modem in a legacy PC, which of the following IRQs would not normally be assigned to the modem?

Introduction / Context:
ISA-era modems required manual configuration of I/O ports and interrupt requests (IRQs). Knowing typical assignments prevents conflicts with other devices like hard-disk controllers and printers. This question asks which IRQ is not appropriate for a modem.

Given Data / Assumptions:

• Legacy ISA resources: common modem COM assignments are to IRQ3 or IRQ4.
• Other IRQs (5, 10) may be available depending on system configuration.
• Standard IDE hard-disk controllers occupy a specific IRQ.

Concept / Approach:

Hard-disk controllers traditionally use IRQ14 (primary IDE). Assigning IRQ14 to a modem would conflict with disk I/O, causing system instability or device failure. Modems typically use IRQ3/4; occasionally IRQ5 or IRQ10 is used in some setups, but not IRQ14.

Step-by-Step Solution:

Verification / Alternative check:

Check Device Manager on AT-class systems; the IDE controller shows IRQ14. Hardware manuals also document this default mapping.

Why Other Options Are Wrong:

IRQ5 and IRQ10 can be valid choices in some configurations; “All of the above” is too broad, and “None of the above” ignores the standard IDE usage of IRQ14.

Common Pitfalls:

Forgetting that printer ports and sound cards historically used IRQ7/5 respectively, and confusing COM port defaults with IDE assignments.

Final Answer:

14