GCSE Computer Science

Content		Additional Information
Understand the following number bases: • decimal (base 10) • binary (base 2) • hexadecimal (base 16).

Understand that computers use binary to represent all data and instructions.		Students should be familiar with the idea that a bit pattern could represent different types of data including text, image, sound and integer.

Explain why hexadecimal is often used in computer science.

Number bases

We usually use Arabic numbers, which are base 10, or decimal. Computers use binary, which is base 2. This page deals with numbers in other bases. Enter a number to convert it to a different base, or count in a base.

How numbers in other bases work

In Arabic numbers (decimal, or base 10), there are 10 digits: 0,1,2,3,4,5,6,7,8,9. You need one digit each to count up to 9, but two digits for ten, and three digits for a hundred, which is ten times ten. In Binary, base 2, you need two digits for two, as you only have two digits, 0 and 1. Base 5 has five digits, and the number five becomes 10. For base 16, you will need sixteen digits, and there are only ten numerals. So we use the letters A,B,C,D,E,F. These represent the decimal numbers 10, 11, 12, 13, 14 and 15. Look at the table below and find the pattern for these bases.

Base 10	Base 2	Base 3	Base 4	Base 5	Base 8	Base 16
1	1	1	1	1	1	1
2	10	2	2	2	2	2
3	11	10	3	3	3	3
4	100	11	10	4	4	4
5	101	12	11	10	5	5
6	110	20	12	11	6	6
7	111	21	13	12	7	7
8	1000	22	20	13	10	8
9	1001	100	21	14	11	9
10	1010	101	22	20	12	A
11	1011	102	23	21	13	B
12	1100	110	30	22	14	C
13	1101	111	31	23	15	D
14	1110	112	32	24	16	E
15	1111	120	33	30	17	F
16	10000	121	100	31	20	10
17	10001	122	101	32	21	11
18	10010	200	102	33	22	12
19	10011	201	103	34	23	13
20	10100	202	110	40	24	14

Base systems like binary and hexadecimal seem a bit strange at first. The key is understanding how different systems “tick over” like an odometer when they are full. Base 10, our decimal system, “ticks over” when it gets 10 items, creating a new digit. We wait 60 seconds before “ticking over” to a new minute. Hex and binary are similar, but tick over every 16 and 2 items, respectively.

3.1 Fundamentals of algorithms

3.2 Programming

3.3 Fundamentals of data representation

3.4 Computer systems

3.5 Fundamentals of computer networks

3.6 Fundamentals of cyber security

3.6.1 Cyber security threats

3.6.2 Methods to detect and prevent cyber security threats

3.7 Ethical, legal and environmental impacts of digital technology on wider society, including issues of privacy

3.8 Aspects of software development

3.8.1 Aspects of software development

Glossary and other links

Glossary of computing terms.

AQA 8520: The 2016 syllabus