Microcontroller definition and integration: A microcontroller places on a single chip what previously required multiple chips—namely, a CPU core together with on-chip RAM, on-chip ROM/flash, and general-purpose I/O peripherals for embedded control.

Introduction / Context:
Microcontrollers are the workhorses of embedded systems. Unlike general-purpose microprocessors that typically require external memory and peripheral chips, microcontrollers integrate core resources on a single die to reduce cost, power, and board space. This question checks whether you recognize that an MCU consolidates CPU, RAM, ROM/flash, and I/O into one device to replace multichip solutions.

Given Data / Assumptions:

• The device under discussion is a microcontroller (MCU), not a general microprocessor (MPU).
• Typical MCU resources include CPU core, RAM, nonvolatile program memory (ROM/flash), and programmable I/O peripherals (timers, GPIO, serial ports).
• External expansion may still be possible but is not required for basic operation.

Concept / Approach:
The hallmark of an MCU is integration. By co-locating memory and I/O with the CPU, the device can start executing from on-chip nonvolatile memory after reset and interact with the outside world via on-chip peripherals. This simplifies design compared with an MPU that commonly boots from external ROM and uses external RAM and discrete I/O controllers.

Step-by-Step Solution:

Verification / Alternative check:
Examine block diagrams of common MCUs (e.g., 8051, AVR, PIC, ARM Cortex-M). Each shows on-chip memories and I/O. Development boards run code from internal flash and use internal SRAM without external devices, confirming the statement.

Why Other Options Are Wrong:

• Incorrect: Contradicts standard MCU architecture.
• Only true for 32-bit devices: 8-bit and 16-bit MCUs have integrated RAM/ROM/I/O, too.
• Only true when external buses are disabled: External buses are optional; integration does not depend on disabling them.
• True only for SoCs, not MCUs: MCUs are a class of SoC focused on control tasks.

Common Pitfalls:
Confusing MCUs with MPUs; assuming all processors need external memory; overlooking that some MCUs optionally add external memory for larger applications but still integrate core resources.

Final Answer:
Correct