Key term
AQA GCSE Computer Science 8525
Algorithms
Programming
Data Representation
Topic overviewNumber bases and why hexadecimal is usedConverting between binary, decimal and hexadecimalUnits of information: bits, bytes and prefixesBinary addition and binary shiftsCharacter encoding: ASCII and UnicodePixels, bitmaps and colour depthBitmap image file size calculationsDigital sound: sampling rate and sample resolutionData compression: Huffman coding and run-length encoding
Computer Systems
Computer Networks
Cyber Security
Relational Databases and SQL
Ethical, Legal and Environmental Impacts of Digital Technology
Algorithms
- 5 subtopics
- 15 things to know
- Paper 1
What Algorithms covers
Algorithms is examined in Paper 1, Computational thinking and programming skills. It covers algorithms, decomposition and abstraction, pseudo-code, flowcharts and trace tables, efficiency of algorithms, linear search and binary search and bubble sort and merge sort.
Where it is assessed
Paper 1
Computational thinking and programming skills, a two-hour paper worth 50% of the GCSE.
Check the AQA specification ↗The 5 subtopics
Each one has its own page.
- Algorithms, decomposition and abstractionWhat an algorithm is and how it differs from a program, why each step must be unambiguous, decomposition and abstraction with worked examples, and the systematic approach to solving a problem.Open →
- Pseudo-code, flowcharts and trace tablesPseudo-code and why programmers design in it, the flowchart symbols for decisions, inputs, outputs and subroutines, trace tables, visual inspection, and short algorithms to trace by hand.Open →
- Efficiency of algorithmsWhat efficiency means, why steps are counted rather than timed, how growing data changes the picture, two ways to sum 1 to 100 or test 101 for prime, and memory as a second measure.Open →
- Linear search and binary searchHow linear and binary searches work, why a binary search needs a sorted list, choosing the middle item, traced searches through short lists, worst cases, and when each search is the better choice.Open →
- Bubble sort and merge sortHow a bubble sort passes through a list and when it stops, how a merge sort splits and merges, traced sorts of short lists, comparison counts, and the strengths of each.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What is output by the algorithm x ← 5, then WHILE x > 1, x ← x − 2, ENDWHILE, then OUTPUT x?
Key term
What is the purpose of the lines temp ← a, then a ← b, then b ← temp?
Process
How does a binary search work?
Process
How does a bubble sort work?
Process
How does a merge sort work?
Process
Describe the steps of a merge sort on [7, 3, 9, 1].
Key term
Can more than one algorithm solve the same problem?
Key term
What is an algorithm?
Key term
What is meant by the efficiency of an algorithm?
Process
How does a linear search work?
Key term
How is an algorithm different from a computer program?
Key term
What is pseudo-code?
Key term
What is time efficiency?
Key term
Does a linear search need the list to be sorted?
Take Algorithms further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Algorithm vs Program
Algorithm: a sequence of steps that completes a task, independent of any language. Program: a set of instructions written in a language a computer can run.
Decomposition vs Abstraction
Decomposition: breaking a problem into smaller sub-problems. Abstraction: removing unnecessary detail from a problem.
Linear search vs Binary search
Linear search: checking each item in turn from the start of a list. Binary search: repeatedly halving an ordered list by comparing with its middle item.
Questions from this topic
Each one with the model answer underneath.
- 1
What is an algorithm?
Model answer
An algorithm is a precise sequence of instructions for carrying out a task. Each step is clear and the steps run in a fixed order.
- 2
How is an algorithm different from a computer program?
Model answer
A program is an algorithm turned into code in one particular language. The algorithm is the underlying method and exists independently of any language.
- 3
Why can the same algorithm be coded in Python, C# or VB.NET?
Model answer
An algorithm describes the logic of a solution rather than the syntax of a language. Any language able to carry out the steps can implement it.
- 4
Is a cooking recipe an algorithm?
Model answer
A recipe is an algorithm because it is a sequence of steps that completes a task. A recipe is not a program, because a person carries it out rather than a computer.
- 5
Why must each step of an algorithm be unambiguous?
Model answer
A step with only one meaning gives the same result whoever follows it. A computer cannot guess what a vague instruction was meant to say.
- 6
What is decomposition?
Model answer
Decomposition is breaking a problem down into smaller sub-problems. Each sub-problem performs one identifiable task and may be broken down further.
What is inside Levo
Six ways to work the same material.
Algorithms revision questions
- What does Algorithms cover in AQA GCSE Computer Science?
- 5 subtopics: algorithms, decomposition and abstraction, pseudo-code, flowcharts and trace tables, efficiency of algorithms, linear search and binary search and bubble sort and merge sort. Each one has its own page with questions and model answers.
- How is Algorithms organised?
- By the AQA 8525 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Algorithms, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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