Fundamentals of PC I/O ports: A COM port on a PC refers to which type of interface?

Introduction / Context:
Legacy PCs expose hardware interfaces with shorthand names. Knowing whether a COM port is serial or parallel helps with cabling, adapters, and configuring peripherals like modems and serial consoles.

Given Data / Assumptions:

• COM1/COM2 are typical labels on IBM-PC compatible systems.
• Used historically for mice, external modems, and serial terminals.
• Electrical standard commonly RS-232 (±3 to ±15 V signaling).

Concept / Approach:

“COM” stands for communication port and denotes an asynchronous serial interface. It transmits data bit-by-bit over a single data line in each direction, unlike parallel ports (LPT) that send multiple bits simultaneously.

Step-by-Step Solution:

Verification / Alternative check:

Loopback tests, terminal programs, or OS device names (e.g., COM1 in DOS/Windows, /dev/ttyS0 in Linux) confirm serial operation with configurable baud and parity parameters.

Why Other Options Are Wrong:

• parallel: That is the LPT port (Centronics/IEEE-1284), not COM.
• static: Not a recognized PC interface type.
• multi: Vague; not specific to COM.
• SCSI: A separate storage/Peripheral bus; unrelated to COM.

Common Pitfalls:

Confusing DB-25 parallel and DB-25 serial pinouts; never cross-use cables. Voltage levels differ from TTL serial (like UART headers), so level shifters are needed for microcontrollers.

Final Answer:

serial