AS Level Computer Science chapter 4: Processor fundamentals MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
33 exam-style questions on Processor fundamentals, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Central Processing Unit (CPU) architecture13 questions
Assembly language11 questions
Bit manipulation9 questions
Ten Processor fundamentals questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. One byte in memory controls eight lights, one bit per light. Why is bit manipulation useful here?
A
it lets all eight lights share one bit
B
it converts the byte to BCD for display
C
one light can be switched without affecting the others
D
it doubles the number of lights that can be controlled
Show answer
Answer: C. With a mask, a single bit can be set, cleared or tested while the other seven bits, and so the other lights, stay unchanged.
2. Why does doubling the number of processor cores not always double performance?
A
each extra core halves the clock speed
B
all cores must share one set of registers
C
the address bus becomes narrower
D
some tasks cannot be split to run in parallel
Show answer
Answer: D. Extra cores help only if the software can divide its work into parts that run at the same time; the cores also have to communicate, which adds overhead.
3. Address 100 contains 7. What is in ACC after this program runs? LDM #4 ADD 100 STO 101 INC ACC ADD 101
A
12
B
23
C
22
D
16
Show answer
Answer: B. LDM #4: ACC = 4. ADD 100: 4 + 7 = 11. STO 101: address 101 = 11. INC ACC: 12. ADD 101: 12 + 11 = 23. 22 forgets the INC.
4. A higher-priority interrupt is accepted. What does the processor do before running the Interrupt Service Routine?
A
saves the current register contents so the task can resume
B
discards the current program and clears its memory
C
finishes all remaining instructions of the current program
D
restarts the computer so the ISR runs from a clean state
Show answer
Answer: A. The contents of registers such as the PC are saved (for example on a stack), the ISR address is loaded into the PC, and afterwards the saved values are restored.
5. A program needs to test whether bit 3 (place value 8) of the accumulator is 1. Which instruction should come before comparing the result with #8?
A
AND #8
B
OR #8
C
XOR #8
D
AND #247
Show answer
Answer: A. AND with the mask 00001000 clears every bit except bit 3; the result is 8 if the bit was set and 0 if not. OR would always set it.
6. The 8-bit two's complement value 11101000 (−24) is given an arithmetic shift right of 2 places. What is the result?
A
00111010
B
11111010
C
10100000
D
11110100
Show answer
Answer: B. An arithmetic right shift copies the sign bit into the vacated places: 11111010 = −6, which is −24 ÷ 4. A logical shift would give 00111010 (+58).
7. The accumulator holds 10010011. What does it hold after a cyclic shift left of one place?
A
00100110
B
11001001
C
01001001
D
00100111
Show answer
Answer: D. In a cyclic shift the bit leaving the left end re-enters on the right: the leading 1 moves to the end, giving 00100111. A logical shift would give 00100110.
8. To which group of instructions does JPE belong?
A
data movement
B
arithmetic operations
C
conditional instructions
D
input and output of data
Show answer
Answer: C. JPE jumps only if the previous compare was True, so it is a conditional jump. JMP is the unconditional jump.
9. Which instruction sets bit 0 of the accumulator to 1 without changing any other bit?
A
AND B00000001
B
OR B00000001
C
XOR B00000001
D
AND B11111110
Show answer
Answer: B. OR with 1 forces a bit to 1 and OR with 0 leaves bits unchanged. XOR would toggle bit 0; AND B11111110 would clear it.
10. The accumulator holds 00010110. What does it hold after LSL #2?
A
00000101
B
10110000
C
01011000
D
10000101
Show answer
Answer: C. Logical shift left 2: every bit moves two places left and zeros enter on the right, giving 01011000 (22 × 4 = 88). 00000101 is a right shift.
33, each with the answer and a short explanation, across 3 topics: Central Processing Unit (CPU) architecture, Assembly language, Bit manipulation. Every chapter test draws ten of them, so you can take it many times.
Is the AS Level Computer Science chapter 4 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
