---
title: "Microcontroller vs microprocessor; 8051 features"
subject: "Embedded System"
chapter: 9
key: "semester_6/embedded_system:micro-vs-microprocessor-8051-features"
source: https://www.bctengineer.com/q/semester_6/embedded_system/micro-vs-microprocessor-8051-features
site: BCT Engineering
---

# Microcontroller vs microprocessor; 8051 features

Embedded System · Chapter 9: Microcontrollers in Embedded Systems

- Asked in: 2078 Chaitra; 2064 Poush (old course) (asked 2 times)
- Video: [Difference between Microprocessor and Microcontroller](https://www.youtube.com/watch?v=dcNk0urQsQM) — ALL ABOUT ELECTRONICS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/embedded_system/micro-vs-microprocessor-8051-features
- Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-9

## Question

How are microcontrollers different from microprocessors? Write the features of 8051 microcontroller.

## Short answer

A microprocessor is a CPU-only chip requiring external memory and I/O; a microcontroller integrates CPU, RAM, ROM, I/O, timers, and serial port on one chip. The 8051 features an 8-bit CPU, 4 KB ROM, 128 B RAM, 32 I/O lines, two 16-bit timers, UART, five interrupt sources with two priority levels, bit-addressable RAM, and on-chip oscillator.

## Answer

A **microprocessor** is a CPU on a chip that needs external memory and I/O chips. A **microcontroller** puts the CPU, RAM, ROM, I/O ports, timers and serial port on a single chip, forming a complete small computer.

#### Difference

| Point | Microprocessor | Microcontroller |
|---|---|---|
| Contents | CPU only | CPU + RAM + ROM + I/O + timers + UART |
| External parts | Memory, I/O chips needed | Few or none |
| Cost, size, power | Higher | Lower |
| Instruction set | Many, for general processing | Few; bit-oriented I/O control |
| Clock speed | High (GHz) | Low (MHz) |
| Use | PCs, servers, general computing | Embedded systems: washing machine, remote, car modules |
| Example | 8085, 8086, Pentium | 8051, PIC, AVR |

#### Features of the 8051

- 8-bit CPU with 8-bit data bus and 16-bit address bus (64 KB code, 64 KB data).
- 4 KB on-chip ROM and 128 bytes on-chip RAM.
- 32 I/O lines in four 8-bit ports (P0-P3).
- Two 16-bit timers/counters (Timer 0 and 1).
- Full-duplex serial port (UART).
- 5 interrupt sources with two priority levels.
- Bit-addressable RAM and SFRs (Boolean processor); special function registers.
- On-chip clock oscillator (11.0592 or 12 MHz crystal); 40-pin DIP.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the main difference between a microprocessor and a microcontroller?
   A. The microprocessor has RAM and ROM on chip
   B. A microcontroller integrates CPU, RAM, ROM, I/O and timers on one chip
   C. Both contain only a CPU
   D. The microcontroller has no CPU
   Answer: B. A microprocessor is a CPU needing external memory and I/O; a microcontroller is a complete small computer on a chip. (Key point: Core difference)

2. Which is a typical use of a microcontroller?
   A. Personal computer
   B. Server
   C. Embedded systems like washing machines
   D. Graphics workstation
   Answer: C. Microcontrollers are used for embedded control; microprocessors for PCs and servers. (Key point: Typical uses)

3. What on-chip memory does the 8051 have?
   A. 64 KB ROM, 64 KB RAM
   B. 128 B ROM, 4 KB RAM
   C. 8 KB ROM, 256 B RAM
   D. 4 KB ROM and 128 bytes RAM
   Answer: D. The 8051 has 4 KB of on-chip ROM and 128 B of RAM. (Key point: 8051 memory)

4. Which set describes the 8051 peripherals?
   A. Two 16-bit timers, one full-duplex UART, 32 I/O lines in four ports
   B. Three 8-bit timers and 2 ports
   C. One timer and SPI
   D. Four timers and 64 I/O lines
   Answer: A. It has two 16-bit timers/counters, a full-duplex UART and four 8-bit ports (32 lines). (Key point: 8051 peripherals)

## Related in Embedded System

- [Microprocessor vs microcontroller; 8051 addressing](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3A8051-addressing-modes-micro-vs-processor) — Embedded System, chapter 9
- [Why 8051 / its operational features](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Awhy-8051-features) — Embedded System, chapter 9, asked 2×

## Related in other subjects

- [Microprocessor vs microcontroller](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Amicroprocessor-vs-microcontroller) — Microprocessor, chapter 1
- [Features of microprocessor based instrumentation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-features) — Instrumentation II, chapter 1, asked 4×