OCR J277 Mark Scheme

OCR	GCSE (9-1) Computer Science Mark Scheme J277/01: Unit 1.2 Character Sets

Question	Answer	Marks	Guidance
1a	A defined list of characters recognised by the computer hardware/software [1] Where each character is represented by a unique binary number/code [1]	2	AO1 (Knowledge) Key concept: "All the characters" and "Unique binary/number". Examiner Note: Do not accept "A list of fonts". It must refer to the mapping of characters to binary.
1b	128	1	AO1 (Knowledge) Accept 2⁷. Examiner Note: Common error is 256 (which is 8-bit). 7-bit is strictly 128.
2a	69	1	AO2 (Application) A=65, B=66, C=67, D=68, E=69. Examiner Note: Students must understand that character codes are logically ordered.
2b	Working: 4 x 7 [1] Answer: 28 (bits) [1]	2	AO2 (Application) The word STOP has 4 characters. If the student assumes 8-bit ASCII (common in older resources), accept 4 x 8 = 32 bits for full marks, as J277 often allows the 8-bit assumption unless specified. However, since "7-bit" was specified in the Q, 28 is the preferred answer.
3a	Benefit: It can represent a wider range of characters / more characters [1] Explanation: Including different languages (Chinese, Arabic, etc.) and emojis [1]	2	AO1 (Knowledge) Examiner Note: Simply saying "It has more bits" is not a benefit; that is a characteristic. The benefit is what you can do with those bits (store languages).
3b	Drawback: It requires more bits per character (e.g., 16 or 32 bits vs 7/8 bits) [1] Explanation: This results in a larger file size / takes up more storage space [1]	2	AO1 (Knowledge) Do not accept "It is slower" (text processing speed is negligible). The main drawback is storage size.
4a	Each key press generates a specific code [1] The computer looks up this code in the Character Set [1] To find the corresponding Binary value for that character [1]	3	AO1 (Knowledge) Max 3 marks. This tests the process of using the set. Students should describe the "lookup" or "conversion" aspect.
4b	Unicode	1	AO2 (Application)
4c	Because ASCII only contains English/Latin characters (128/256) and cannot represent the thousands of symbols needed for Chinese/Emojis.	1	AO2 (Application) Must reference the limitation of ASCII or the capability of Unicode regarding the specific requirement (Chinese/Emojis).