Legacy PC hardware – Which device typically uses IRQ 6?

Introduction / Context:
On classic x86 PCs, hardware devices were assigned specific Interrupt Request (IRQ) lines. Recognizing these historical defaults helps when troubleshooting legacy systems and for certification exams that still reference them.

Given Data / Assumptions:

• Traditional PIC (8259)-based IRQ mapping on DOS/early Windows systems.
• No Advanced Programmable Interrupt Controller (APIC) remapping or Plug-and-Play overrides.
• Standard peripherals installed (keyboard, floppy, IDE, VGA).

Concept / Approach:

Common defaults: IRQ1 = keyboard, IRQ3/4 = serial COM ports, IRQ5/7 = LPT/sound variations, IRQ6 = floppy disk controller, IRQ14/15 = primary/secondary IDE. Hence IRQ6 is associated with the floppy subsystem.

Step-by-Step Solution:

Verification / Alternative check:

Check BIOS setup or DOS utilities (e.g., MSD) from historical environments: the floppy controller is listed on IRQ6.

Why Other Options Are Wrong:

Keyboard is IRQ1; IDE uses 14/15; VGA generally relies on memory-mapped I/O rather than a dedicated fixed IRQ; USB controllers are later additions with PCI IRQ routing.

Common Pitfalls:

Confusing COM port IRQs (3/4) with floppy; assuming modern Plug-and-Play layouts match legacy fixed assignments.

Final Answer:

Floppy drive controller.