Introduction
We know that earlier electronic devices were made up of vacuum tubes or valves

Vacuum tubes or Valves:
- The evolution of vacuum tubes started with diode and proceeded to triode, tetrode and pentode
- Valves control the flow of electrons; In diodes, there were two electrodes – cathode and anode
- Similarly, triode had three electrodes – cathode, grid and anode; tetrode had four electrodes – anode, two grids and cathode; pentode had five electrodes –anode, three grids and cathode
- Generally in vacuum tubes, the electrons are produced by heating the cathode using low tension battery; The vacuum helps in electron not losing its energy by collision with air molecules in the way
- However, the vacuum tube devices had some disadvantages and they are
- Bulky
- Operate at high voltages
- Consume more power
- Have limited life
- Low reliability
Diodes and transistors
- Next came the discovery of semiconductor junction, namely, junction diode and transistors
- These replaced the vacuum tubes or valves

- The advantages of semiconductor devices are
- Small in size
- Operate at low voltages
- Consume small power
- Long life
- High reliability
- Though the above advantages are present, the circuits consisting of transistors were still bulky, less shock proof
- Hence, it led to the discovery of integrated circuits which is a major revolution in the electronic industry
Example – The earlier generation television and computer monitors were very bulky as they were based on the principle of vacuum tubes; now days, we have LCD (Liquid Crystal Display) monitors which support solid state electronics
