Computers manipulate binary patterns.
Complete the table to show the 8-bit result of the binary addition.
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
|---|---|---|---|---|---|---|---|
| 1 | 0 | 1 | 1 | 1 | 0 | 0 | 1 |
| 1 | 0 | 1 | 1 | 1 | 1 | 0 | 0 |
Mark scheme
Award one mark for each correct nibble in the correct order:
- 0111 (1)
- 0101 (1)
0 marks if the response is not 8-bit binary.
Ignore a carry shown beyond the eighth bit.
Example answers and how they were marked
0111 0101
Why: 185 + 188 = 373, which needs 9 bits; the 8 bits that are kept are both correct (2).
0000 0101
Why: Forgets to carry the 1s. The second nibble is correct (1); the first is not.
1011 1101
Why: Never carries. Neither nibble is correct.
State the name of the error that occurs when this addition is carried out.
Mark scheme
Award one mark for:
- overflow (error) (1)
Example answers and how they were marked
Overflow
Why: The result needs more bits than are available (1).
Underflow
Why: A near miss: the result is too big for 8 bits, not too small.
A syntax error
Why: A syntax error is a mistake in a program's code, not in arithmetic.