history of a microcontroller

The first single chip microprocessor was the 4 bit Intel 4004 released in 1971, with other more capable processors available over the next several years.
These however all required external chip(s) to implement a working system, raising total system cost, and making it impossible to economically computerise appliances.
The first computer system on a chip optimised for control applications - microcontroller was the Intel 8048 released in 1975[citation needed], with both RAM and ROM on the same chip. This chip would find its way into over one billion PC keyboards, and other numerous applications.
Most microcontrollers at this time had two variants. One had an erasable EEPROM program memory, which was significantly more expensive than the PROM variant which was only programmable once.
In 1993, the introduction of EEPROM memory allowed microcontrollers (beginning with the Microchip PIC16x84) to be electrically erased quickly without an expensive package as required for EPROM, allowing both rapid prototyping, and In System Programming.
The same year, Atmel introduced the first microcontroller using Flash memory.
Other companies rapidly followed suit, with both memory types.
Cost has plummeted over time, with the cheapest 8-bit microcontrollers being available for under $0.25 in quantity (thousands) in 2009, and some 32-bit microcontrollers around $1 for similar quantities.
Nowadays microcontrollers are low cost and readily available for hobbyists, with large online communities around certain processors.
In the future, MRAM could potentially be used in microcontrollers as it has infinite endurance and its incremental semiconductor wafer process cost is relatively low.

reason to use microcontroller

Interrupt latency
In contrast to general-purpose computers, microcontrollers used in embedded systems often seek to minimize interrupt latency over instruction throughput.
When an electronic device causes an interrupt, the intermediate results, the registers, have to be saved before the software responsible for handling the interrupt can run, and then must be put back after it is finished. If there are more registers, this saving and restoring process takes more time, increasing the latency.
Low-latency MCUs generally have relatively few registers in their central processing units, or they have "shadow registers", a duplicate register set that is only used by the interrupt software.

types of microcontroller

Types of microcontrollers
This section requires expansion.
As of 2008 there are several architectures:

* 68HC11
* 8051
* ARM
* Atmel AVR 8-bit architecture
* Atmel AVR32 32-bit architecture
* Freescale CF (32-bit)
* Freescale S08
* Hitachi H8, Hitachi SuperH
* MIPS (32-bit PIC32)
* NEC V850
* PIC (8-bit PIC16, PIC18, 16-bit dsPIC33 / PIC24)
* PowerPC ISE
* PSoC (Programmable System-on-Chip)
* Rabbit 2000
* TI MSP430 (16-bit)
* Toshiba TLCS-870
* Zilog eZ8, eZ80
and many others, some of which are used in very narrow range of applications or are more like processors than microcontrollers.