A flip flop is a two state device which can store two stable states which find widespread use as memories for sequential logic operations in the form of register banks. These are clocked edge-triggered devices specially designed for synchronous systems. The change in state of these devices can take place only on a rising/falling edge or both, but not as level triggers. The most common types of flip-flops are ‘SR’, ‘D’,’T’ and ‘JK’. Often termed as the basic building blocks of digital electronics systems, these are built using cross-coupled inverting elements like BJTs, FETs etc.