Character Encoding: ASCII and Unicode

Computers store all data as binary numbers, including text. A character encoding system assigns a unique binary number to each character (letter, digit, symbol). OCR J277 Section 2.6 requires you to understand both ASCII and Unicode.

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What Is Character Encoding?

A character encoding is a mapping between characters and numbers. When you type the letter "A" on a keyboard, the computer stores a number (65 in ASCII). When the computer displays that number, it shows the character "A" on screen.

Every character must have a unique number, and both the sender and receiver of data must agree on which encoding system to use. Otherwise, characters may be displayed incorrectly.

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ASCII (American Standard Code for Information Interchange)

ASCII was developed in the 1960s and uses 7 bits per character, giving 2^7 = 128 possible characters. These include:

Range	Characters	ASCII codes
Uppercase letters	A-Z	65-90
Lowercase letters	a-z	97-122
Digits	0-9	48-57
Punctuation and symbols	! @ # etc.	Various
Control characters	Enter, Tab, Backspace	0-31
Space	(space)	32

Key ASCII Values to Know

Character	ASCII (denary)	ASCII (binary, 7-bit)
A	65	1000001
B	66	1000010
Z	90	1011010
a	97	1100001
0	48	0110000
Space	32	0100000

OCR Exam Tip: You do not need to memorise the entire ASCII table, but you should know that A = 65, a = 97, and 0 = 48. Notice that lowercase letters are 32 higher than their uppercase equivalents.

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Extended ASCII

Standard ASCII uses 7 bits, but most computers use 8-bit bytes. Extended ASCII uses all 8 bits, providing 2^8 = 256 characters. The extra 128 characters include accented letters (e.g., e, u), additional symbols, and line-drawing characters.

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Limitations of ASCII

ASCII has significant limitations: