Command Words (Cambridge (CIE) A Level Computer Science): Revision Note
Exam code: 9618
What are command words?
Why do command words matter in 9618?
A command word is the instruction at the start of an exam question, such as State, Describe or Explain
It tells you what kind of answer the examiner wants and how much detail to give
Cambridge examiner reports for 9618 regularly advise students to learn the meanings of the command words and to "form their answers accordingly"
A correct fact written in the wrong form can still lose marks; for example, a one-word answer to an Explain question will rarely score
The most common command words in 9618
The 9618 syllabus lists 27 command words, but a small number make up most of the questions
In recent papers, the most frequent are Write, Describe, Complete, Explain, State and Identify
Paper 1 uses Describe and Explain the most
Papers 2 and 3 use Write the most: in Paper 2 it usually asks for pseudocode, and in Paper 3 it also asks for Boolean expressions, Reverse Polish Notation (RPN), declarative clauses and floating-point values
Command word | What it means (Cambridge definition) | What to do in 9618 | Real 9618 example |
|---|---|---|---|
State | Express in clear terms | Give a short, precise answer; no explanation needed | State the purpose of the system clock and the Control Unit (CU) in a CPU |
Identify | Name, select or recognise | Name the item; one word or a short phrase is often enough | Identify two differences between general purpose registers and special purpose registers |
Give | Produce an answer from a given source or from memory | Give the number of points asked for, each one separate | Give two benefits of distributing software using a shareware software licence |
Define | Give precise meaning | Give the exact meaning of the term, using technical vocabulary | Define cloud computing |
Outline | Set out the main points | Give the main points briefly, without full detail | Outline two benefits and two limitations of a virtual machine |
Describe | State the points of a topic, or give characteristics and main features | Say what something is or what happens, step by step; each step is usually a mark | Describe how the laser printer makes use of a buffer |
Explain | Set out purposes or reasons, make the relationships between things clear, or say why and/or how and support with relevant evidence | Give a point and the reason for it, linked with "because" or "so that" | Explain what is meant by disk thrashing |
Write | Write an answer in a specific way | Produce the answer in the form asked for: pseudocode, Structured Query Language (SQL), a Boolean expression | Write the Boolean expression that corresponds to the logic circuit as a sum-of-products |
Complete | Add information to an incomplete diagram or table | Fill in every empty cell or part; do not change what is already given | Complete the trace table by dry running the procedure |
Calculate | Work out from given facts, figures or information | Show each step of the working; no calculator is allowed | Calculate the normalised floating-point representation of +54.8125 in this system |
Command words that students confuse
State, Describe or Explain?
These three words ask about the same topic at three different depths
State asks what: one clear fact
Describe asks what happens: the features or the steps, in order
Explain asks why or how: each point needs a reason
Examiners point out that an Explain question needs more detail than an Identify question
If an Explain question is worth 2 marks, aim for one point and its reason, or two linked points
Identify or Outline?
Identify only needs the name of the thing; extra detail will not gain more marks
Outline needs the main points of each item, briefly
"Outline two methods of overcoming this issue" needs a short description of how each one works
If the same question used Identify instead, the names of two methods would be enough
Evaluate means "work out the value"
In most subjects, Evaluate means making a judgement
In 9618 papers, Evaluate is used to ask for the value of an expression, matching the second half of the Cambridge definition: "judge or calculate the quality, importance, amount, or value of something"
"Evaluate this RPN expression" means work out the numeric result
"Evaluate each expression in the table by using the data values shown" means work out what each expression returns (for example,
TRUE,FALSEor a number)
Write the final value clearly and, where asked, show the stack contents or working that produced it
Compare and contrast
Compare asks for similarities and/or differences; Contrast asks for differences only
Every point must mention both items
"A linear search checks every item in turn, whereas a binary search halves the search area each time" scores
"A binary search halves the search area each time" on its own does not, because it says nothing about a linear search
Draw in 9618
The syllabus defines Draw as "draw a line to match a term with a description", and 9618 papers do use it this way
9618 papers also use Draw for diagrams, such as:
logic circuits
structure charts
syntax diagrams
loops around groups in a Karnaugh map
Use a ruler, follow the symbol conventions used in the question and label everything the question asks for
Worked Example
A student sends a long document from a laptop to a printer.
(a) State what is meant by a buffer.
[1]
(b) Describe how a buffer is used when the document is printed.
[3]
(c) Explain why a buffer is needed when the document is printed.
[2]
Answer:
(a) A temporary area of memory that holds data while it is being transferred between devices [1 mark]
(b) Any three from:
The laptop sends data for the document to the buffer [1 mark]
The printer takes data from the buffer at its own speed [1 mark]
When the buffer is empty, an interrupt is sent to the laptop [1 mark]
... requesting more data to be sent [1 mark]
(c) The laptop sends data much faster than the printer can print it [1 mark]
... so the buffer holds the data and the processor can carry on with other tasks instead of waiting for the printer [1 mark]
Part (a) needs one fact, part (b) needs the steps in order, and part (c) needs a reason, so the same topic is worth 1, 3 or 2 marks depending on the command word.
Examiner Tips and Tricks
Before you answer, circle the command word and check the marks: an Explain question worth 2 marks needs a point and a reason, not two separate facts
If a question uses Evaluate with an expression, it wants a value, so do not write a paragraph judging the expression
Command words in programming and working-out questions
Write
Write is the most common command word in Papers 2 and 3
In 9618 it usually asks for an answer in a specific form:
"Write pseudocode for the function..."
"Write a Structured Query Language (SQL) script to..."
"Write the Boolean expression that corresponds to..."
When Write asks for pseudocode, it must follow the Cambridge pseudocode conventions; marks are lost for using programming language syntax instead
See Writing Pseudocode in the Exam for the conventions examiners check
Complete
Complete asks you to fill in something that is partly given, such as a trace table, a truth table, an assembly language trace or a Backus-Naur Form (BNF) definition
Use the format already in the table; for example, if a column shows values in binary, do not switch to denary
In a trace table, write a value only when it changes; in a truth table, fill in every cell
Show
Show is not in the syllabus list, but it appears often in Papers 1 and 3
"Show your working" means the method earns marks, not just the answer
"Show the changing contents of the stack" means write out every state, not only the final one
"Show the result of a 2-place left logical shift" means write the resulting binary number in full
Other command words in the 9618 syllabus
These words are in the syllabus list but appear rarely in 9618 papers
Command word | What it means |
|---|---|
Analyse | Examine in detail to show meaning, identify elements and the relationship between them |
Assess | Make an informed judgement |
Comment | Give an informed opinion |
Consider | Review and respond to given information |
Demonstrate | Show how or give an example |
Develop | Take forward to a more advanced stage or build upon given information |
Discuss | Write about issue(s) or topic(s) in depth in a structured way |
Examine | Investigate closely, in detail |
Predict | Suggest what may happen based on available information |
Sketch | Make a simple freehand drawing showing the key features, taking care over proportions |
Suggest | Apply knowledge and understanding to situations where there is a range of valid responses, in order to make proposals or put forward considerations |
Summarise | Select and present the main points, without detail |
Justify is the exception: it is common in 9618, usually as "Justify your choice" or "justify your answer"; give a reason linked to the scenario, saying why your choice suits it better than the alternative, not just how each works
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