In market there are a number of micro-controller available some of them are following.
8051,Atmel-AVR , Microchip -PIC , NXP-Dallas,Reanses etc.
In a micro-controller has ,In build Clock to produce pulse it determine the speed of the MCU (Mico controller Unit). it seems 12MHz,20MHZ discus later
Have I/O ports .that means these port can be used both input or out put according to our decision.
It have Analog to Digital & digital to analog converter.