Legacy PC resources: For classic ISA-era sound cards, which IRQ was most commonly used by default for audio devices?

Introduction / Context:
Before Plug and Play standardized resource allocation, ISA expansion cards required manual configuration of I/O addresses, IRQs, and DMA channels. Sound Blaster-compatible cards had de facto defaults that avoided conflicts with serial and parallel ports.

Given Data / Assumptions:

• We refer to legacy ISA sound cards (Sound Blaster and compatibles).
• Common IRQs for built-in ports: COM1 uses IRQ4; LPT1 uses IRQ7.
• The goal is to recall the typical default IRQ for audio.

Concept / Approach:

To minimize conflicts, many sound cards defaulted to IRQ5, leaving IRQ7 available for the LPT1 printer port. Some systems also allowed IRQ7, but IRQ5 became the widely used default for audio. Higher or lower IRQs were possible but less common due to conflicts or limited driver support.

Step-by-Step Solution:

Verification / Alternative check:

Vendor manuals and DOS installers show default settings such as I/O 0x220, IRQ5, DMA1 for 8-bit audio and DMA5 for 16-bit on some models.

Why Other Options Are Wrong:

• IRQ4: usually COM1; using it could break serial communications.
• IRQ7: used by LPT1 by default; sometimes used by audio but not the most common default.
• IRQ8: tied to the real-time clock (system), inappropriate for a sound card.
• None of the above: incorrect because IRQ5 is correct and common.

Common Pitfalls:

Assuming plug-and-play will always resolve ISA conflicts; forgetting to change both IRQ and DMA; overlooking TSRs and drivers that lock resources.

Final Answer:

IRQ5