In basic data communications, what is the name of the device used to connect two computers over a telephone line by converting digital data to analog waveforms and back again?

Introduction:
Before ubiquitous broadband, many computers communicated via public switched telephone networks. A specific endpoint device converted digital bits into analog audio tones suitable for the voice band and then reversed the process at the far end. Understanding this legacy but still-relevant device helps ground key concepts of modulation and demodulation.

Given Data / Assumptions:

• Communication medium: voice-grade telephone line.
• End systems: digital computers that produce and consume bits.
• Need: translate between digital domain and analog channel.

Concept / Approach:
The correct device is a modem (from modulator-demodulator). The transmitter side modulates a carrier (varying amplitude, frequency, or phase), and the receiver side demodulates to recover the original bitstream. Although modern broadband uses different physical layers, the conceptual role of modems persists in DSL, cable, cellular, and satellite systems where digital data rides on passband signals.

Step-by-Step Solution:
1) Identify the mismatch: digital bits vs. analog telephone channel.2) Use a device that modulates at the sender and demodulates at the receiver.3) Name that device: modem.4) Validate by typical standards (e.g., V.90, V.92) historically used over PSTN lines.

Verification / Alternative check:
Legacy dial-up Internet connections used modems on both ends; today, cable and cellular modems perform analogous functions with more advanced waveforms.

Why Other Options Are Wrong:

• Tape: storage medium, not a communication interface.
• Bus: internal computer interconnect concept, not a phone-line interface device.
• Cable: a passive medium; it does not perform modulation/demodulation.
• None of the above: incorrect because modem fits precisely.

Common Pitfalls:
Confusing the medium (telephone line) with the active device (modem) that makes the line usable for digital data.

Final Answer:
modem