Key term
OCR GCSE Computer Science J277
Systems Architecture
Memory and Storage
Topic overviewRAM, ROM, cache and virtual memorySecondary storage: magnetic, optical and solid stateData units and storage capacity calculationsBinary, denary and hexadecimal conversionsBinary addition, overflow and binary shiftsCharacter sets, ASCII and UnicodeBitmap images, colour depth and resolutionSound sampling, sample rate and bit depthLossy and lossless compression
Computer Networks, Connections and Protocols
Network Security
Systems Software
Ethical, Legal, Cultural and Environmental Impacts of Digital Technology
Algorithms
Programming Fundamentals
Producing Robust Programs
Programming Languages and Integrated Development Environments
Algorithms
- 5 subtopics
- 15 things to know
- J277/02
What Algorithms covers
Algorithms is examined in J277/02, Computational thinking, algorithms and programming. It covers abstraction, decomposition and algorithmic thinking, Flowcharts, pseudocode and structure diagrams, trace tables and correcting algorithms, linear and binary search and bubble, merge and insertion sort.
Where it is assessed
J277/02
Computational thinking, algorithms and programming, 1 hour 30 minutes and 50% of the GCSE.
Check the OCR specification ↗The 5 subtopics
Each one has its own page.
- Abstraction, decomposition and algorithmic thinkingComputational thinking, abstraction and decomposition with worked examples, algorithmic thinking, what an algorithm is, and how the principles work together to solve a problem.Open →
- Flowcharts, pseudocode and structure diagramsInputs, processes and outputs, structure diagrams, pseudocode, the flowchart symbols for decisions, inputs and outputs, sub programs and loops, and nesting.Open →
- Trace tables and correcting algorithmsTrace tables and why they are used, the output of short algorithms in Exam Reference Language, and finding and fixing errors in given code.Open →
- Linear and binary searchHow linear and binary searches work, why a binary search needs sorted data, the midpoint calculation, worked searches through short lists, and the strengths of each.Open →
- Bubble, merge and insertion sortHow bubble, merge and insertion sorts work, worked passes through short lists, merging two sorted lists, and how the three sorts compare.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
A school wants a program to book parents' evening appointments. Give one example of each principle of computational thinking.
Process
What are the inputs, processes and outputs of a problem?
Process
A program asks for the length and width of a rectangular room and displays its floor area. Identify the inputs, process and output.
Key term
Describe how a binary search works.
Key term
How is the middle position calculated in a binary search?
Key term
A binary search looks for 23 in [2, 5, 9, 14, 23, 31, 40]. Which items are compared with 23?
Numbers
How many passes does a bubble sort need to put [6, 3, 8, 1] into ascending order?
Process
Describe the steps of an insertion sort on [5, 2, 7, 1].
Key term
Describe how a merge sort sorts [6, 2, 8, 5].
Key term
What is a trace table?
Key term
Explain why trace tables are used.
Key term
What is computational thinking?
Key term
What is a structure diagram?
Key term
What is output by the algorithm n = 1, do, n = n * 3, until n > 20, print(n)?
Take Algorithms further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Abstraction vs Decomposition
Abstraction: removing detail that does not affect the solution to a problem. Decomposition: breaking a problem down into smaller sub-problems.
Pseudocode vs Flowchart
Pseudocode: structured English-like statements that describe the steps of an algorithm. Flowchart: a diagram of standard connected shapes showing the steps of an algorithm.
Linear search vs Binary search
Linear search: checking each item in turn from the first until the target is found. Binary search: comparing a target with the middle item of a sorted list and discarding half.
Questions from this topic
Each one with the model answer underneath.
- 1
What is computational thinking?
Model answer
Computational thinking is a way of analysing a problem so that a computer can help to solve it. The three principles are abstraction, decomposition and algorithmic thinking.
- 2
Define abstraction.
Model answer
Abstraction is removing detail that is not needed to solve a problem. Only the details that affect the solution are kept.
- 3
Why is abstraction useful when a problem is being defined?
Model answer
Abstraction makes a problem simpler, so the programmer can focus on what matters. A simpler model is quicker to design, code and test.
- 4
A program predicts where a snooker ball will travel after it is struck. Which details would abstraction keep and which would it remove?
Model answer
The model keeps the ball's position, speed and direction, and the angles of the cushions. Details such as the colour of the cloth and the players' names are removed.
- 5
How does a sat nav app use abstraction?
Model answer
A sat nav shows roads, junctions and the route as simple lines and symbols. Buildings, trees and most scenery are left out because they do not affect the journey.
- 6
What can go wrong if abstraction removes too much detail?
Model answer
A model that ignores an important detail gives inaccurate results. A weather forecast that left out wind speed would make poor predictions.
What is inside Levo
Six ways to work the same material.
Algorithms revision questions
- What does Algorithms cover in OCR GCSE Computer Science?
- 5 subtopics: abstraction, decomposition and algorithmic thinking, flowcharts, pseudocode and structure diagrams, trace tables and correcting algorithms, linear and binary search and bubble, merge and insertion sort. Each one has its own page with questions and model answers.
- How is Algorithms organised?
- By the OCR J277 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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