2.4 Computational Logic

2.4 Computational Logic

1. Why is data represented in binary form?

   • This is because, underneath the surface, computers are electrical devices that process information by controlling the flow of electricity through billions of wires and switchesinside the CPU, memory chips and between components.
   • The flow of electricity down a single cable or through a switch can be represented in binary as a 1, whereas a cable or switch without electricity flowing through it can be represented as a 0.
   • As an example, an 8-bit binary number such as 01101101 represents the flow of electricity through a group of 8 wires or, if the data is stored in memory, the state of 8 individual transistors.
   • So, the bits in a binary number represent the flow of electricity through individual wires and switches within the components of a computer system.

2. Transistors

   • Transistors are electrical components made from semiconductor materials that can act as electrically-controlled switches.
   • A common way to think of transistors is that they are like taps. When a tap is turned on, water coming into the tap is allowed to flow through the tap and to come out.
   • In a transistor, when the "base" input on a transistor has a small current flowing through it, the larger current entering the transistor from the "collector" can flow through to the the "emitter".

3. Logic Gates

   • Multiple transistors can be arranged together to form more complex "switches" that only allow electricity to flow through if all or some of the transistors are "on".
   • Such arrangements of transistors are called logic gates - they act like gates that only open if certain logical conditions are met.
   • There are three types of logic gate that you must be familiar with at GCSE - AND, OR and NOT logic gates.

4. Logic circuits

   • Logic gates can be combined to form logic circuits that process complex logical statements such as A AND (B OR C).
   • The output of logic statements in brackets become input to 'outer' logical operations.
   • Conventionally, input labels start at A (A, B, C, etc.) whereas output labels start at Q (Q, R, S, etc.).