A
multivibrator is an electronic
circuit which in its simplest form consists of two
transistors. The circuit can exist in either of two states, neither of which is stable. The length of time spent in each state is determined by a
resistor/
capacitor combination which drives the base of each of the transistors. The commonest form is that where the two states are equally shared in time. Such a device can be used as an electronic clock but in practice is too sensitive to external factors such as temperature to be useful as a time reference. However, multivibrators are at the heart of many electronic musical instruments defining the fundamental pitch of a note.
Computer use of multivibrators come in three types: astable (where neither state is stable but the circuit oscillates between at least two states); monostable (where one state is stable, the other transient). And bistable multivibrators, where the circuit can be flipped from state one to state two. The fact that it can be 'flopped' back again leads to the important 'flip-flop' device. The key to defining memory-processing registers.