PC IRQ conventions: Historically, which hardware interrupt request (IRQ) line was most commonly assigned to ISA Sound Blaster–compatible sound cards?
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AIRQ 5
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BIRQ 6
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CIRQ 15
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DIRQ 1
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EIt does not use an IRQ
Answer
Correct Answer: IRQ 5
Explanation
Introduction / Context:Legacy ISA devices required unique IRQ lines to signal the CPU. Classic Sound Blaster–compatible sound cards needed a dedicated IRQ for audio events. Knowing the common defaults helps resolve conflicts on vintage systems.
Given Data / Assumptions:
- Context is ISA-era PCs (DOS/Win9x), not modern PCI/PCIe plug-and-play.
- Common peripherals also occupied well-known IRQs (e.g., keyboard on IRQ 1).
- We are asked which IRQ was typically used by Sound Blaster–type cards.
Concept / Approach:
Sound Blaster cards commonly defaulted to IRQ 5 (sometimes configurable to IRQ 7). IRQ 7 was often used by LPT1 (parallel printer), so IRQ 5 avoided conflicts while remaining a standard SB setting. Thus, IRQ 5 is the best answer.
Step-by-Step Solution:
Recall keyboard uses IRQ 1; floppy controller uses IRQ 6.Parallel port often uses IRQ 7; network cards could use various IRQs.Sound Blaster default selections: IRQ 5 or 7, with 5 being the more common conflict-free choice.Select IRQ 5 as the historically typical assignment.Verification / Alternative check:
Sound card manuals and SET BLASTER environment strings (e.g., A220 I5 D1 H5) corroborate IRQ 5 as a frequent default.
Why Other Options Are Wrong:
- IRQ 6: generally floppy disk controller.
- IRQ 15: typically secondary IDE or available for other devices.
- IRQ 1: reserved for keyboard.
- It does not use an IRQ: incorrect for ISA sound cards.
Common Pitfalls:
Forgetting to change printer port IRQ or disable LPT when using IRQ 7 for the sound card; mixing DMA/IRQ settings leading to no audio in DOS games.
Final Answer:
IRQ 5