Ports and Connectivity: Where Would You Attach a Traditional External Modem? Identify the appropriate PC interface used by legacy external dial-up modems.

Introduction / Context:
Before broadband and USB, external dial-up modems connected to a computer using asynchronous serial communication (RS-232). Correctly identifying the proper legacy port helps when supporting older equipment in labs or industry.

Given Data / Assumptions:

• External modem with DB-25 or DB-9 connector.
• PC equipped with COM ports (serial, asynchronous).
• Null modem and straight-through cabling considerations apply.

Concept / Approach:

An external modem interfaces via an asynchronous serial (ASYNC) port, commonly labeled COM1/COM2 and presented as DB-9 or DB-25 connectors. Parallel (LPT) ports are for printers; keyboard and video ports do not carry serial modem signals.

Step-by-Step Solution:

Verification / Alternative check:

Use a loopback plug on the COM port to ensure the port is working, then connect the modem and test with AT commands (e.g., “AT”, “ATI”, “ATDT”).

Why Other Options Are Wrong:

Parallel port is for printers/legacy devices using different signaling (Centronics/IEEE 1284). Keyboard and video ports are unrelated. “None of the above” is incorrect because the asynchronous serial port is the correct answer.

Common Pitfalls:

Using a null modem cable instead of a straight-through one for modem connection, or misconfiguring flow control (RTS/CTS vs. XON/XOFF).

Final Answer:

ASYNC port