A Level Computer Science (A2) MCQs with answers
Practise A Level Computer Science (A2) (9618) with 428 exam-style MCQs, each with the answer and a short explanation. Every test is marked the moment you finish and shows your score chapter by chapter, so you know what to revise next. It is free and needs no sign-up.
428 questions · 8 chapters
What each chapter covers 8 chapters
The questions follow the syllabus chapter by chapter. You can test the whole subject or one chapter at a time.
- Data Representation 76 questionsUser-defined data types, File organisation and access, Floating-point numbers, representation and manipulation
- Communication and internet technologies 42 questionsProtocols, Circuit switching, packet switching
- Hardware and Virtual Machines 68 questionsProcessors, Parallel Processing and Virtual Machines, Boolean Algebra and Logic Circuits
- System Software 67 questionsPurposes of an Operating System (OS), Translation Software
- Security 29 questionsEncryption, Encryption Protocols and Digital Certificates
- Artificial Intelligence (AI) 27 questions
- Computational thinking and Problem-solving 60 questionsAlgorithms, Recursion
- Further Programming 59 questionsProgramming Paradigms, File Processing and Exception Handling
Sample A Level Computer Science (A2) MCQs with answers 12 questions
12 questions from the test, one or two from each chapter. Try each one, then open the answer.
1. In a sequential file, how are the records arranged?
- A
in the order in which they were created
- B
in the order in which they were last read
- C
at addresses calculated by a hashing algorithm
- D
in order of a key field
Show answer
Answer: D. A sequential file keeps the records sorted on a key field, such as a customer number. A file in order of creation is serial.
2. When a message is sent from one host to another, each layer of the sending host's protocol stack adds its own information to the data. What is this information called?
- A
a header
- B
a key
- C
a checksum table
- D
an address bus
Show answer
Answer: A. Each layer wraps the data from the layer above with its own header (encapsulation). The receiving host's layers remove the headers in reverse order.
3. Which is a limitation of a virtual machine?
- A
programs generally run more slowly than on real hardware
- B
it can run only one single type of program at any one time
- C
it cannot ever be copied or deleted once made
- D
it is always faster than running natively on the host
Show answer
Answer: A. The extra software layer between the guest and the hardware adds overhead, and the virtual machines share the host's processor, memory and disk.
4. A program has a syntax error in a branch of code that is never executed on a test run. What happens with an interpreter?
- A
the program will not start at all when it is run by the user
- B
the error is reported before any statement has been run
- C
the program may run to completion without the error being noticed
- D
the interpreter will correct the error by itself as it runs
Show answer
Answer: C. An interpreter checks each statement only when it reaches it, so a faulty statement that is never reached is not reported. A compiler would report the error while translating the whole program.
5. The cipher text 10011100 was produced by XOR with the key 00110101. What is the plain text?
- A
10101001
- B
00010100
- C
10111101
- D
01010110
Show answer
Answer: A. XOR with the same key reverses the encryption, because (P XOR K) XOR K = P. 10011100 XOR 00110101 = 10101001.
6. A satnav program stores a road network as a graph. What do the weights on the edges most sensibly represent?
- A
the distance or travel time of each road section
- B
the number of houses on each road section
- C
the name of the town at each junction
- D
the number of vertices already visited
Show answer
Answer: A. The weight of an edge is the cost of using it, such as distance or journey time. The search algorithm adds these costs along a route to find the cheapest one.
7. Which is an advantage of a linked list over an array when a new item has to be inserted in the middle of a sorted list?
- A
the items can be found more quickly by a binary search
- B
less memory is used because pointers do not need to be stored
- C
the items can be accessed directly by their index
- D
no existing items need to be shifted; only pointers are changed
Show answer
Answer: D. Inserting into an array means moving every later item along, but in a linked list only two pointers change. The cost is the extra memory for pointers and no direct access by position.
8. In the instruction LDM #75, which addressing mode is used?
- A
direct
- B
indirect
- C
indexed
- D
immediate
Show answer
Answer: D. In immediate addressing the operand is the value itself, so 75 is loaded straight into the accumulator with no memory access for the operand.
9. Which statement about overflow and underflow in a floating-point system is correct?
- A
increasing the mantissa bits makes both less likely
- B
they can only occur when a mantissa is negative
- C
increasing the exponent bits makes both less likely
- D
they can only occur when numbers are not normalised
Show answer
Answer: C. Overflow and underflow are limits of the exponent's range, so more exponent bits widen the range and make them less likely. More mantissa bits improve precision, not range.
10. Which is a benefit of circuit switching?
- A
the links are shared efficiently between many different users
- B
the connection can be set up instantly, with no delay at all
- C
if one link fails, the data is sent by another route instead
- D
the data arrives in order at a constant rate
Show answer
Answer: D. The reserved path gives a steady rate and no reordering, which suits real-time speech. Sharing links and re-routing around failures are features of packet switching.
11. Which is a valid size for a group of cells in a Karnaugh map?
- A
8 cells
- B
3 cells
- C
5 cells
- D
6 cells
Show answer
Answer: A. Groups must contain 1, 2, 4, 8 or 16 cells, a power of 2, and be rectangular, and the largest groups are used. Sizes of 3, 5 and 6 do not correspond to a simpler product term.
12. How does a round-robin scheduler share the processor?
- A
the process with the shortest burst time always runs first and to the end
- B
each process runs until it completes, in order of arrival
- C
the process that arrived last is always the one that runs first
- D
each process runs for a fixed time slice, then rejoins the ready queue
Show answer
Answer: D. In round robin, each process gets the same time slice and then the next ready process is given the processor, so no process waits too long.
Try 416 more questions
Ways to practise 5 ways
- Quick check. 10 questions drawn fresh each time, about 10 minutes.
- By chapter. 10 questions from one chapter, for the topic you are revising now.
- Full paper. A full-length timed paper across the whole syllabus.
- Practice mode. See the right answer and an explanation after every question, with no clock.
- Exam mode. Timed like the real paper, with no going back.
When you get a question wrong, a short note called "The idea behind this" explains the topic it belongs to, with the rules to remember and a worked example.
Common questions
Is this A Level Computer Science (A2) test free?
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Are these past paper questions?
The 428 MCQs are our own, written to the syllabus in the style of the exam.
How is the test marked?
Instantly. You get your score, the right answer and an explanation for every question, and a list of the topics to work on.
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