In a typical PC-to-telephone long-distance data connection, where is the modem placed in relation to the computer’s I/O—between the telephone line and which computer interface?

Introduction / Context:
Traditional dial-up connectivity used modems to convert digital serial data to analog waveforms suitable for telephone networks. PCs interfaced with external modems through serial ports implementing RS-232, which are asynchronous serial interfaces.

Given Data / Assumptions:

• External modem used for telephone line connection.
• PC provides standard legacy serial ports (COM1/COM2) using RS-232.
• Interface timing is asynchronous (start/stop bits), not synchronous clocked serial.

Concept / Approach:
External dial-up modems connect to the PC via an asynchronous serial port (UART-based), typically exposed as a COM port. The other side of the modem connects to the analog telephone line (POTS). Synchronous serial ports exist but are not typical for consumer PC modem connections.

Step-by-Step Solution:
Identify the PC-modem link: RS-232 serial (UART) → asynchronous.Identify the modem-line link: analog POTS line via RJ-11.Therefore, the modem sits between the phone line and the PC’s asynchronous serial port.

Verification / Alternative check:
Common external modems used DB-9/DB-25 RS-232 connectors to COM ports; internal modems implemented the same interface on an expansion card but still presented an asynchronous interface to the OS.

Why Other Options Are Wrong:
PC (internal bus directly): Internal modems do, but the question states a PC-to-telephone hookup—external modem context.

Synchronous port: Not the usual interface for consumer dial-up modems.

Crossover cable: Ethernet wiring concept, irrelevant here.

Parallel printer port: Not used for standard modems.

Common Pitfalls:
Confusing “serial” with “synchronous.” RS-232 modems use asynchronous framing (start/stop bits) at the PC side.

Final Answer:
asynchronous port