Characters are encoded using 7-bit ASCII.
Identify the number of different characters that can be represented using 7-bit ASCII.
Mark scheme
- C 128 (1)
- The only correct answer is C. The correct answer is 128.
- A is not correct because 6 bits give only 64 different combinations
- B is not correct because 127 is the largest 7-bit value, not the number of characters that 7 bits can represent
- D is not correct because 256 characters need 8 bits, as used by 8-bit extended ASCII
Example answers and how they were marked
Full marks1/1
C 128
Why: Selects the only correct option (1): 7 bits give 2 to the power of 7, which is 128 different characters.
No marks0/1
D 256
Why: Near miss scoring 0: 256 is the number of characters that 8 bits give in extended ASCII, not 7-bit ASCII.
No marks0/1
B 127
Why: Misconception scoring 0, the off-by-one error the examiners' report describes: 127 is the largest 7-bit value, but 7 bits give 128 different characters.