OCR J277 - Character Sets Revision Tool

1 [3 Marks Total]

(a) Define the term 'Character Set'. [2]

(b) The ASCII character set uses 7 bits.
State the maximum number of different characters that can be represented. [1]

✅ Mark Scheme

(a) Definition:

A defined list of characters recognised by the computer. (1)
Where each character is mapped to a unique binary number. (1)

(b) Max Characters: 128 (2^7)

Score yourself (Max 3):

2 [3 Marks Total]

A computer uses ASCII. 'A' is code 65.

(a) State the denary code for 'E'. [1] (b) Calculate the total file size of the word STOP in bits (7-bit ASCII used). Show working. [2]

✅ Mark Scheme

(a) 69 (A=65, B=66, C=67, D=68, E=69)

(b) Answer: 28 bits

(Working: 4 characters x 7 bits per char = 28)

Score yourself (Max 3):

3 [4 Marks Total]

Most modern computers use Unicode instead of ASCII.

(a) Explain one benefit of using Unicode. [2] (b) Explain one drawback of using Unicode. [2]

✅ Mark Scheme

(a) Benefit:

Can represent many more characters/languages (Emoji, Chinese, etc.). (1)
Because it uses more bits per character. (1)

(b) Drawback:

Larger file size / Takes up more storage. (1)
Because each character uses 16/32 bits instead of 7/8. (1)

Score yourself (Max 4):

4 [5 Marks Total]

A programmer is creating a messaging app.

(a) Explain how a character set is used to convert key presses into binary. [3] (b) Which character set is best for Emojis and Chinese symbols? [1]

(c) Justify your choice. [1]

✅ Mark Scheme

(a) Process:

Key press generates a specific code. (1)
Computer looks up the code in the Character Set. (1)
Finds the corresponding binary value. (1)

(b) Choice: Unicode

(c) Justification: ASCII is too small (only 128/256 chars). Need thousands of characters for Chinese/Emojis.

Score yourself (Max 5):