Legacy Modem Fundamentals In traditional PC communications, external and internal dial-up modems exchange data with the computer using which style of data transmission (bit timing and framing method)?

Introduction / Context:
Classic dial-up modems interfaced with PCs long before broadband and USB became common. Understanding how a modem frames and times data clarifies why serial port settings like baud rate, data bits, parity, and stop bits matter. This question asks which transmission style a modem uses when talking to the computer's serial (COM) port.

Given Data / Assumptions:

• PC hosts communicate with external or internal modems via a serial interface.
• Settings such as 8-N-1 (8 data bits, no parity, 1 stop bit) are familiar defaults.
• The telephone network path between two modems is analog; the PC-to-modem link is digital serial.

Concept / Approach:

On the PC side, modems use asynchronous serial transmission. Each character is framed by a start bit and one or more stop bits, with optional parity. There is no separate clock line; timing is derived from the configured baud rate. While modems can perform complex synchronous protocols over the phone line, the host connection itself is almost universally asynchronous for desktop use.

Step-by-Step Solution:

Verification / Alternative check:

Terminal programs (e.g., HyperTerminal, PuTTY) require asynchronous settings (8-N-1) to communicate with AT-command modems. This operational fact confirms the answer.

Why Other Options Are Wrong:

Synchronous requires shared clocking not present on classic PC COM links. “Timed interval,” “ata,” and “bank” are not valid transmission modes for serial communication.

Common Pitfalls:

Confusing the modem-to-modem line protocol with the PC-to-modem interface. The PC side is asynchronous even if modems negotiate complex protocols over the phone line.

Final Answer:

asynchronous