PC hardware — Which chip handles legacy serial (COM) port communications on IBM-PC compatibles?

Introduction / Context:
PC serial ports (COM1–COM4) use a Universal Asynchronous Receiver/Transmitter (UART) to convert between parallel bus data and serial bit streams. Technicians often need to recognize common UART models and their functions.

Given Data / Assumptions:

• Legacy ISA/PCI systems with standard COM ports.
• Typical UART model numbers include 8250, 16450, and 16550.
• Question asks for the device that controls serial communication.

Concept / Approach:

The 16550 UART introduced FIFO buffering to improve throughput and reduce CPU interrupts, becoming the de facto standard for reliable serial communication on PCs.

Step-by-Step Solution:

Verification / Alternative check:

Motherboard and I/O card documentation list 16550 or compatible cores for COM ports.

Why Other Options Are Wrong:

ROM BIOS initializes hardware but is not the serial hardware engine; the CPU runs drivers but does not replace a UART; DMA823 is unrelated to serial line coding.

Common Pitfalls:

Confusing DMA controllers with serial controllers, or assuming the BIOS “does the work” beyond initialization.

Final Answer:

UART 16550.