A
typical Relay
A
typical ValveIntroduction to Digital Computers - 2
In early computers the 'switches' were electro-mechanical devices called "relays". When an electric current passes through the coil of a relay it produces a magnetic field. A small piece of iron is attracted to the coil and activates switch contacts. Relays are quite slow and require quite a lot of current. Faster switching was available using "valves".
| A
typical Relay |
A
typical Valve |
A valve is like a tap that controls the flow of electricity instead of water. Small currents flowing into part of the valve are used to control larger currents. A valve can switch much faster than a relay and unlike a relay there are no moving parts to wear out.