Legacy PC hardware: What is the standard hexadecimal I/O base address for COM3 (serial port 3)?

Introduction / Context:
Classic IBM PC-compatible systems map serial ports to fixed I/O addresses and IRQs. Knowing these mappings is crucial for low-level troubleshooting, legacy OS configuration, and resolving resource conflicts with add-in cards or embedded devices.

Given Data / Assumptions:

• Standard legacy assignments: COM1 and COM2 occupy well-known base addresses.
• COM3 and COM4 extend the scheme using alternate base addresses and the same IRQs as COM1/COM2.
• Question asks specifically for COM3 I/O base address (hexadecimal).

Concept / Approach:
The canonical PC serial-port base addresses are: COM1 = 3F8h (IRQ 4), COM2 = 2F8h (IRQ 3), COM3 = 3E8h (typically IRQ 4), and COM4 = 2E8h (typically IRQ 3). These addresses are widely used in BIOS and operating systems of the DOS/Windows 9x era and remain a knowledge staple for technicians working with legacy hardware.

Step-by-Step Solution:

Verification / Alternative check:
Motherboard or expansion-card manuals list these addresses. System utilities (MSD, debug, or device-manager resources in older Windows) also report configured port addresses consistent with these defaults.

Why Other Options Are Wrong:

• 345, ff8, 5e8, be8: Do not match the standard serial base-address set for COM ports.

Common Pitfalls:
Confusing IRQ assignments with I/O addresses, or mixing COM3 (3E8h) with COM1 (3F8h) due to the similar high nibble.

Final Answer:
3e8