From 5 to 3.3 V

Many microcontrollers these days are powered from 3.3 V (or oven lower voltages) instead of the old, familiar 5 V. Lowering the dissipation and increasing the switching speed are the main considerations for reducing the power supply voltage. In addition, the ever continuing miniaturisation results in transistors inside the ICs that are so small that the breakdown-voltage has become much lower and a 5-V power supply would cause problems.