IGCSE Computer Science Paper 2 Definitions Worksheet: 10 Boolean Logic (Modules 552–561)
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Key terms
Write what each term means, in your own words.
1
X = A XOR B
2
XOR
3
output circle
4
output column
5
X = A AND B
6
(A AND B) OR C
7
NOT (A AND B)
8
000 to 111
9
intermediate column
Answer Key
IGCSE Computer Science Paper 2 · Modules 552–561 · Student wording will vary for definitions
1X = A XOR B — The XOR (exclusive OR, or EOR) gate has two inputs and outputs 1 only when the inputs are different. Its truth table output is 0 1 1 0. Its symbol is the OR shape with an extra curve at the input.
2XOR — Exclusive OR: outputs 1 when exactly one input is 1. When A and B are both 1 it outputs 0, but OR outputs 1 in that row. XOR means one or the other, but not both.
3output circle — A small circle on a gate's output means NOT: AND becomes NAND and OR becomes NOR. XOR has no circle; its symbol is OR with an extra curved line at the input side.
4output column — Read the output column for rows 00, 01, 10, 11 to name the gate: AND 0001, OR 0111, NAND 1110, NOR 1000, XOR 0110.
5X = A AND B — A logic expression for one gate: write the output X, an equals sign, then the input letters joined by the gate name in capitals, such as X = NOT A or X = A XOR B.
6(A AND B) OR C — Brackets show which gate is worked out first. Here A AND B is done first, then its result goes into OR with C. A AND (B OR C) uses the same letters but gives a different output.
7NOT (A AND B) — NOT before a bracket flips the whole bracket's result. In (NOT A) AND B, NOT flips only input A, so NOT (A AND B) gives different results.
8000 to 111 — A three-input truth table has 8 rows (2 x 2 x 2) in binary counting order from 000 to 111, with A changing slowest and C changing fastest.
9intermediate column — An extra truth table column for a bracket or gate output, such as P = A AND B. It is filled in first, so the final output X can be worked out step by step from earlier columns.