The classic EIA-232 (RS-232-C) serial interface originally specified a 25-pin connector. How many pins are present on this standard connector?

Introduction / Context:
EIA-232 (often known by its historical name RS-232-C) defines electrical characteristics and signal assignments for serial communications between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE). While many PCs later adopted a smaller 9-pin connector, the original standard interface used a larger 25-pin connector with defined signal pins for control and data.

Given Data / Assumptions:

• We are referring to the classic EIA-232/RS-232-C connector as originally standardized.
• The question asks for the number of pins on that standard connector.
• Later variants (DE-9) exist but do not change the original pin count.

Concept / Approach:
The original RS-232-C physical interface specified a DB-25 connector with 25 pins. These pins include transmit data, receive data, signal ground, and numerous control leads (e.g., RTS, CTS, DTR, DSR, DCD, RI). Many applications used only a subset, which is why the industry later favored the compact DE-9 connector that multiplexed key signals into 9 pins, but the standardized full connector remains 25-pin.

Step-by-Step Solution:

Verification / Alternative check:
Pinout references list DB-25 pin assignments for RS-232-C. Serial adapters and legacy modems commonly expose DB-25 ports, confirming the 25-pin count even if modern PCs commonly present DE-9 ports for convenience.

Why Other Options Are Wrong:

• 20/24/30: not the standardized DB-25 count for RS-232-C.
• 9: applies to the later DE-9 connector, not the original RS-232-C connector in the question.

Common Pitfalls:
Assuming all RS-232 connectors are 9-pin because of later PC hardware; overlooking that the standard historically describes a 25-pin interface.

Final Answer:
25