OCR GCSE Computer Science (J277) · Computer systems (Paper 1) › Memory and storage › Data storage
Practise Characters: ASCII and Unicode. 12 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Standard ASCII uses 7 bits for each character. State how many different characters it can represent.
128
State how many different characters can be represented using an 8-bit character set.
256
In ASCII, and so also in Unicode, the lower-case letter 'a' has the character code 97. State the character with the code 100.
d
Sample questions
Written for this site in the style of OCR exam questions. They are not taken from real past papers.
Question 1Easy3 marks
(a) State what is meant by a character set.[1]
(b) Standard ASCII uses 7 bits for each character. State how many different characters it can represent.[1]
(c) Which one of these can represent characters from most of the world's languages? Tick (✓) one box.[1]
ASCII
Binary
Hexadecimal
Unicode
Show the answer and mark scheme
(a)
all the characters that a computer can represent, each with its own unique binary code
(b)Answer: 128
128
(c)Answer: Unicode
Question 2Medium4 marks
(a) Explain why Unicode was developed.[2]
(b) Explain one disadvantage of using Unicode instead of ASCII.[2]
Show the answer and mark scheme
(a)
ASCII can only represent a small number of characters (128 / 256)
which is not enough for other languages / alphabets / symbols / emoji, so Unicode uses more bits to represent many more characters
(b)
Unicode uses more bits for each character
so text files are larger / take up more storage / take longer to send
Question 3Hard4 marks
In ASCII, the character code for the digit '0' is 48.
(a) State the character code for the digit '7'.[1]
(b) A program stores the character '7' typed by a user. It then adds 5 to the character's code, expecting to get 12. Explain why the result is not 12.[2]
(c) Describe how the program could be corrected.[1]
Show the answer and mark scheme
(a)Answer: 55
55
(b)
the character '7' is stored as its character code (55), not as the number 7
so the program calculates 55 + 5 = 60
(c)
convert (cast) the character to an integer before adding / subtract 48 from the character code first