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    Online Learner Guide
    Cambridge International AS & A Level Computer Science 9618 - for examination from 2021




    • Syllabus content - what you need to know about


    • There are four components that you will need to take:

        • Paper 1 (Theory Fundamentals)

        • Paper 2 (Fundamental Problem-solving and Programming Skills)

        • Paper 3 (Advanced theory)
        • Paper 4 (Practical)


      Key concepts

      Key concepts are essential ideas that help you to develop a deep understanding of your subject and make links between different aspects of the course. The key concepts for Cambridge International AS & A Level Computer Science are:

      • Computational thinking

      Computational thinking is a set of fundamental skills that help produce a solution to a problem. Skills such as abstraction, decomposition and algorithmic thinking are used to study a problem and design a solution that can be implemented. This may involve using a range of technologies and programming languages.

      • Programming paradigms

      A programming paradigm is a way of thinking about or approaching problems. There are many different programming styles that can be used, which are suited to unique functions, tools and specific situations. An understanding of programming paradigms is essential to ensure they are used appropriately, when designing and building programs.

      • Communication

      Communication is a core requirement of computer systems. It includes the ability to transfer data from one device or component to another and an understanding of the rules and methods that are used in this data transfer. Communication could range from the internal transfer of data within a computer system, to the transfer of a video across the internet.

      • Computer architecture and hardware 

      Computer architecture is the design of the internal operation of a computer system. It includes the rules that dictate how components and data are organised, how data are communicated between components, to allow hardware to function. There is a range of architectures, with different components and rules, that are appropriate for different scenarios.

      All computers comprise of a combination of hardware components, ranging from internal components, such as the Central Processing Unit (CPU) and main memory, to peripherals. To produce effective and efficient programs to run on hardware, it is important to understand how the components work independently and together to produce a system that can be used. Hardware needs software to be able to perform a task. Software allows hardware to become functional. This enables the user to communicate with the hardware to perform tasks.

      • Data representation and structures 

      Computers use binary and understanding how a binary number can be interpreted in many different ways is important. Programming requires an understanding of how data can be organised for efficient access and/or transfer. 

      These key concepts help you to gain:

      • a greater depth as well as breadth of subject knowledge 

      • confidence, especially in applying your knowledge and skills in new situations

      • the vocabulary to discuss the subject conceptually and show how different aspects link together

      • a level of mastery of their subject to help them enter higher education. 


      Make sure you always check the latest syllabus, which is available at www.cambridgeinternational.org.





    • How you will be assessed
    • Please rotate your device



    • What skills will be assessed?

    • The examiners take account of the following skills areas (assessment objectives) in the examinations:

      AO1: Knowledge with understanding
      Demonstrate knowledge and understanding of the principles and concepts of computer science including abstraction, logic, algorithms and data representation.
      AO2: Application
      Apply knowledge and understanding of the principles and concepts of computer science, including to analyse problems in computational terms.
      AO3: Design, program and evaluation
      Design, program and evaluate computer systems to solve problems, making reasoned judgements about these.



    • Command words

    • The flipcards below include command words used in the assessment for this syllabus.
      The use of the command word will relate to the subject context.



    • Example candidate response

    • All information and advice in this section is specific to the example question and response being demonstrated. It should give you an idea of how your responses might be viewed by an examiner but it is not a list of what to do in all questions. In your own examination, you will need to pay careful attention to what each question is asking you to do.

    • Question

      The question used in this example is from Paper 3 and and requires knowledge and understanding of the TCP/IP stack, together with knowledge of protocols and understanding of what they are used for and how they are used.

      2) The TCP/IP protocol suite can be viewed as a stack with four layers.
      (a) Complete the stack by inserting the names of the three missing layers.


      Complete is the command word in this question. This means that you add information to an incomplete diagram.

      b) BitTorrent is a protocol used at the Application layer for an exchange of data.
      i) State the network model used with this protocol.

      State is the command word in this question. This means that you should write the answer clearly and succinctly, you may only need to use a few words.

      ii) State the use of BitTorrent.

      iii) Explain how applications use BitTorrent to exchange data.

      Explain how are the command words in this question. This means that you should set out the method used to perform the given task showing that you understand how the method used is applied to the situation set out in the question..

      (c) State two other protocols that are used at the Application layer for the exchange of data.

      For each protocol, give a different example of an appropriate exchange of data.

      Give is the command word in this question. This means that you should recall from your own knowledge.
    • Markscheme - Paper 3 - Question 2

    • Please rotate your device

    • Example candidate response and examiner comments

    • (a)
      Application layer
      Transport (layer)
      Internet (layer)
      Network (access layer)

      [See examiner comment]

      (b)
      (i) Peer – to – peer.

      (ii) File sharing.

      (iii) BitTorrent client software is made available, this is used to load the torrent descriptor for the required file by computers joining it swarm. A server, called tracker, keeps records of all the computers joining the swarm and allows them to connect to each other by sharing their IP addresses.

      The torrent is split into small pieces that can be downloaded or uploaded by each computer in the swarm. Once a computer has downloaded a piece of the torrent file it can upload that piece to other computers in the swarm and become a seed.

      (c)
      Protocol 1 SMTP
      Example Sending email messages
      Protocol POP3
      Example retirement of email messages

      [See examiner comment]

      [Total mark awarded]



    • Download the full learner guide to explore the Example Candidate Response further:



    • Revision

    • Explore the advice below to help you revise and prepare for the examinations.  It is divided into general advice for all papers and more specific advice for each of the papers.


    • General advice - before the examination
      • Find out when the examinations are and plan your revision so you have enough time for each topic. A revision timetable will help you
      • Find out how long each paper is and how many questions you have to answer
      • Know the meaning of the command words used in questions and how to apply them to the information given. Highlight the command words in past papers and check what they mean. There is a list on page 11 of this guide
      • Make revision notes; try different styles of notes. See the Learner Guide: Planning, Reflection and Revision which as ideas about note-taking. Discover what works best for you
      • Work for short periods then have a break. Revise small sections of the syllabus at a time
      • Build your confidence by practising questions on each of the topics
      • Make sure you practice lots of past examination questions so that you are familiar with the format of the examination papers. You could time yourself when doing a paper so that you know how quickly you need to work in the real examination
      • Look at mark schemes to help you understand how the marks are awarded for each question
      • Make sure you are familar with the technical terminology that you need for this syllabus. Your teacher will be able to advise you on what is expected.
      General advice - during the examination
      • Read the instructions carefully and answer all the questions
      • Check the number of marks for each question or part question. This helps you to judge how long you should be spending on the response. You don't want to spend too long on some questions and then run out of time at the end
      • Do not leave out questions or parts of questions. Remember, no answer means no mark
      • If a question has several parts, then the parts with more marks will need more time and more developed answers
      • You do not have to answer the questions in the order they are printed in the answer booklet. You may be able to do a later question more easily then come back to an earlier one for another try
      • Read each question very carefully. Misreading a question can cost you marks:
        • Identify the command words – you could underline or highlight them
        • Identify the technical terms and perhaps underline them too
        • Try to put the question into your own words to understand what it is really asking.
      • Read all parts of a question before starting your answer. Think carefully about what is needed for each part. You will not need to repeat material
      • Answer the question. This is very important!
        • Use your knowledge and understanding
        • Do not write everything you know about a topic. Only use the information you need to answer the question.
      • Make sure that you have answered everything that a question asks. Sometimes one part requires two things, e.g. 'Calculate...' and 'Show your working.'. It is easy to concentrate on the first request and forget about the second one
      • Always show your working. Marks are usually awarded for using correct steps in the method even if you make a mistake somewhere
      • Don't cross out any working in a calculation until you have replaced it by trying again. Even if you know it's not correct you may still be able to get method marks. If you have made more than two attempts, make sure you cross out all except the one you want marked
      • Make sure all your numbers are clear, for example make sure your '1' doesn't look like a '7'
      • If you need to change a word or a number, it is better to cross out your work and rewrite it. Don't try to write over the top of your previous work as it will be difficult to read and you may not get the marks
      • Don't write any pseudocode answers in two columns in the examination. It is difficult for the examiners to read and follow your working.
      Advice for Papers 1 and 3
      • Always use the logic gate symbols from the syllabus when drawing logic circuits
      • Always use the opcodes given on the syllabus or shown on the examination paper when writing assembly language instructions
      • Try and use capital letters when writing assembly language opcodes, SQL, or pseudocode commands so they can be clearly recognised as commands by the examiner
      • Where possible use SQL and pseudocode commands that are given in the syllabus, any other commands should be identified and explained.
      Advice for Paper 2
      • Try and use capital letters when writing pseudocode commands so they can be clearly recognised as commands by the examiner
      • Where possible use pseudocode commands that are given in the syllabus, any other commands should be identified and explained
      • Annotate pseudocode with comments
      • Fully label diagrams.
      Advice for Paper 4
      • Remember you will need to write and test programs in the examination
      • Only use one of the recommended programming languages for your answers:
        • Java
        • Visual Basic
        • Python
      • Be able to use your chosen programming language in console mode
      • Get plenty of practice at debugging and testing programs using your chosen programming language
      • Where possible use the same programming language for all your answers.


    • Consider your confidence with each topic area.
      Download the full learner guide to see the detailed expectations for each topic.
      Drag colour option


    • Paper 1 - Theory Fundamentals
    • 1.1 Data Representation
      1.2 Multimedia
      1.3 Compression
      1.4 Communication
      1.5 Hardware
      1.6 Processor Fundamentals
      1.7 System Software
      1.8 Security, privacy and data integrity
      1.9 Ethics and ownership
      1.10 Databases
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    • Paper 2 - Fundamental Problem-solving and Programming Skills
    • 2.1 Computational thinking skills
      2.2 Algorithm Design
      2.3 Data types and structures
      2.4 Programming
      2.5 Software Development
      TEXT
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    • Paper 3 - Advanced Theory
    • 3.1 Data Representation
      3.2 Communication and internet technologies
      3.3 Hardware
      3.4 System Software
      3.5 Security
      3.6 Artificial Intelligence (AI)
      3.7 Algorithms
      TEXT
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    • Paper 4 - Practical
    • 4.1 Programming


    • Download the full learner guide to make use of the full guidance and revision checklists: