DMA Resource for Floppy Controller On legacy PCs, the floppy disk controller (FDC) uses which ISA DMA channel for data transfers?

Introduction / Context:
ISA-era systems assign fixed DMA channels to certain controllers. Recognizing these defaults helps diagnose resource conflicts and configuration issues. The floppy disk controller is one of the classic examples with a well-known DMA assignment.

Given Data / Assumptions:

• Standard PC/AT mapping with dual 8237 DMA controllers (8-bit and 16-bit channels).
• A conventional floppy disk drive and controller are present.
• We are referring to ISA-based systems.

Concept / Approach:

The FDC conventionally uses 8-bit DMA channel 2 for data transfers. Other standard mappings include DMA channel 3 for LPT (in some modes) and higher channels for 16-bit devices. Remembering “FDC → DMA 2” is a common A+ and hardware exam fact.

Step-by-Step Solution:

Verification / Alternative check:

View Device Manager on old systems or BIOS setup to confirm the FDC uses DMA 2. Vendor manuals also list this mapping.

Why Other Options Are Wrong:

Channels 1, 4, 5, and 9 are not the default for the floppy controller in ISA PCs. Hence, option “2” is uniquely correct.

Common Pitfalls:

Confusing IRQs (e.g., FDC uses IRQ6) with DMA channels, or mixing up printer DMA usage with floppy.

Final Answer:

2