Edexcel GCSE Computer Science: grade by grade

Every skill, from the first marks to the top grade. For each grade you also need the skills for the grades below it. Tick them off in the app's Notes section.

Grade 3

Grade 3 checklist (PDF)

Define decomposition Breaking a problem down into smaller sub-problems that are each easier to understand and solve. Decomposition and abstraction
Define abstraction Removing or hiding unnecessary detail so that you can focus on what matters for the problem. Decomposition and abstraction
Name the standard flowchart symbols Terminal, process, decision, input/output and subprogram symbols, joined by arrows. Flowcharts, pseudocode and program code
Define variable and constant A variable's value can change while the program runs; a constant's value does not. Variables, constants and data structures (strings, arrays and records)
Use the four basic arithmetic operators Add, subtract, multiply and divide, knowing that / gives a real number. Arithmetic, relational and logical operators
Follow a short sequence to find the output Work through a few assignments and a print statement in order. Tracing algorithms and trace tables
Name the three types of error Syntax, logic and runtime errors. Syntax, logic and runtime errors
Describe how a linear search works Check each item in turn from the start until the item is found or the list ends. Linear and binary search
State the outputs of AND, OR and NOT AND needs both inputs to be 1; OR needs at least one; NOT reverses its input. Truth tables and logic
State why computers use binary Computers are built from switches (transistors) that have two states, on and off, which represent 1 and 0. Binary representation and unsigned binary–denary conversion
Name the kinds of data stored in binary Numbers, text, images, sound and program instructions are all stored as binary patterns. Binary representation and unsigned binary–denary conversion
Define a character set A list of the characters a computer can represent, each with its own unique binary code. Characters and ASCII
Define pixel The smallest single-coloured element (dot) of a bitmap image. Bitmap images
State that sound is analogue Sound is a continuous wave, so it must be sampled before it can be stored in binary. Sound
Put the units of storage in order bit, nibble, byte, kibibyte, mebibyte, gibibyte, tebibyte. Units and file size calculations
Give reasons for compressing files Compressed files use less storage space and transfer faster, using less bandwidth. Lossless and lossy compression (incl. RLE)
State what main memory holds Main memory (RAM) holds the program instructions and the data that are currently in use. Stored program concept and von Neumann architecture
Name the four main parts of the CPU Control unit (CU), arithmetic logic unit (ALU), registers and clock. CPU components and the fetch–decode–execute cycle
Define volatile and non-volatile Volatile memory (RAM) loses its contents when the power is off; non-volatile storage keeps them. Main memory and secondary storage
Give examples of each type of storage Magnetic: hard disk drive; optical: CD, DVD, Blu-ray; solid state: SSD, USB flash drive, memory card. Main memory and secondary storage
Define an embedded system A computer system inside a larger device that carries out a dedicated function. Embedded systems
Give examples of embedded systems For example a washing machine, microwave oven, central heating thermostat, car engine management system or traffic lights. Embedded systems
State the purpose of an operating system It manages the hardware and software, and provides a platform for applications and an interface for the user. Operating systems
Name the four functions of an operating system File management, process management, peripheral management and user management. Operating systems
State the purpose of utility software It maintains, protects or improves the performance of a computer system. Utility software
Name the five utilities in the specification File repair, backup, data compression, disk defragmentation and anti-malware. Utility software
Define robust software Software that keeps working correctly, without crashing, even with unexpected input or when attacked. Robust software: audit trails and code reviews
State what machine code is Instructions in binary that the CPU can execute directly, without translation. Programming languages and translators
State what LAN and WAN stand for LAN stands for local area network and WAN stands for wide area network. LANs, WANs and why computers are connected
Define the internet The internet is a worldwide network of interconnected networks. The internet: IP addressing and routers
State how data travels in each medium Electrical signals in copper cable, pulses of light in fibre-optic cable and radio waves for Wi-Fi. Wired and wireless connectivity and performance
State the unit of network speed Network speed is measured in bits per second (bps), with kbps, Mbps and Gbps for larger rates. Network speeds and transmission time
Define a network protocol A protocol is a set of rules that govern how data is transmitted between devices. Protocols
Name the four layers in order From the top: application, transport, internet, link. The TCP/IP model
Identify bus, star and mesh from diagrams Bus: one backbone cable; star: every device cabled to a central switch; mesh: devices joined to several others. Network topologies
Give reasons why network security is important To stop data being stolen, changed or deleted, and to keep systems working. Network security and identifying vulnerabilities
State the purpose of a firewall A firewall blocks unauthorised traffic entering or leaving a network. Protecting networks
Define e-waste E-waste is electronic and electrical equipment that has been thrown away, such as old phones, laptops and chargers. Environmental issues
Give environmental problems of making devices Mining raw materials damages habitats, factories use a lot of energy and water, and both cause pollution. Environmental issues
Define personal data Information about a living person who can be identified from it, such as a name, address or photo. Personal data: privacy, ownership, consent and data protection
Give examples of personal data collected For example name, date of birth, email address, location, bank details and health information. Personal data: privacy, ownership, consent and data protection
Define artificial intelligence AI is a computer system that carries out tasks that normally need human intelligence, such as recognising speech. Artificial intelligence, machine learning and robotics
Give uses of AI and robots For example, medical scan analysis, fraud detection, chatbots, self-driving cars and warehouse robots. Artificial intelligence, machine learning and robotics
State what copyright protects Original work such as source code, images, music and text; the protection applies automatically. Intellectual property and licensing
Match a protection method to an item Code → copyright, invention → patent, logo or name → trademark, permission to use software → licence. Intellectual property and licensing
Define malware and give examples Malware is software designed to cause harm, e.g. viruses, worms, Trojans, ransomware and key loggers. Malware, social engineering and technical vulnerabilities
Give ways to protect against malware Up-to-date anti-malware, installing patches promptly, and not opening unexpected attachments or links. Protecting digital systems and data (incl. encryption)
Define encryption, plaintext, ciphertext and key Encryption uses an algorithm and a key to turn plaintext into ciphertext that cannot be understood without the key. Protecting digital systems and data (incl. encryption)
Name the three types of program error Syntax, logic and runtime errors, with an example of each. Developing code: readability, errors, validation and testing
Recognise sequence, selection and iteration in code Point out the lines that run in order, the lines that make a decision and the lines that repeat. Sequence, selection and iteration
Name the primitive data types Integer, real, Boolean and character, which Python stores as int, float, bool and str. Data types and data structures
Take input and display output Use input() with a clear prompt and print() to show the results. Input, output and file handling
Use +, −, * and / correctly Know that / always gives a real result, e.g. 8 / 2 gives 4.0. Operators
Call built-in subprograms such as len() Use pre-existing subprograms such as len(), print(), int() and round() with the right arguments. Subprograms and libraries

Grade 4

Grade 4 checklist (PDF)

Give benefits of decomposition Sub-problems are simpler, can be shared across a team, tested separately and reused. Decomposition and abstraction
Identify sequence, selection and repetition Spot each construct in a flowchart, in pseudocode or in Python code. Flowcharts, pseudocode and program code
Follow an algorithm to find its output Work through a flowchart or program step by step with the inputs given. Flowcharts, pseudocode and program code
Access an array item by its index Indexes start at 0, so scores[2] is the third item. Variables, constants and data structures (strings, arrays and records)
Use relational operators to compare values Use ==, !=, <, >, <= and >= to give True or False. Arithmetic, relational and logical operators
Trace a simple loop in a trace table Record each variable's new value on each pass through the loop. Tracing algorithms and trace tables
Describe each type of error Syntax breaks the language rules; logic gives wrong results; runtime crashes while running. Syntax, logic and runtime errors
State that binary search needs sorted data A binary search only works if the list is in order. Linear and binary search
Carry out one pass of a bubble sort Compare adjacent pairs from left to right and swap any pair in the wrong order. Bubble sort and merge sort
Describe how a bubble sort works Repeat passes of comparing and swapping adjacent items until a pass makes no swaps. Bubble sort and merge sort
Count comparisons in a linear search Count how many items are checked before the target is found or the list ends. Efficiency of algorithms
Complete a truth table with two inputs Four rows: 00, 01, 10, 11. Truth tables and logic
Convert 8-bit binary to denary Add the place values (128, 64, 32, 16, 8, 4, 2, 1) of every column that holds a 1. Binary representation and unsigned binary–denary conversion
Convert denary 0 to 255 into binary Work from 128 downwards, writing 1 for each place value you can subtract and 0 for each you cannot. Binary representation and unsigned binary–denary conversion
Recognise a negative two's complement number In two's complement, a 1 in the most significant bit means the number is negative. Two's complement
Use the four binary addition rules 0 + 0 = 0, 0 + 1 = 1, 1 + 1 = 0 carry 1, and 1 + 1 + 1 = 1 carry 1. Binary addition and overflow
Apply a logical shift left Move every bit left by the given number of places and fill the gaps on the right with 0s. Logical and arithmetic shifts
Apply a logical shift right Move every bit right by the given number of places and fill the gaps on the left with 0s. Logical and arithmetic shifts
Recall the hex digits 0–9 and A–F A = 10, B = 11, C = 12, D = 13, E = 14 and F = 15. Hexadecimal
State that one hex digit is 4 bits 16 different digits need 4 bits, because 2⁴ = 16. Hexadecimal
State how many characters 7-bit ASCII represents 7 bits give 2⁷ = 128 different codes, from 0 to 127. Characters and ASCII
Define resolution and colour depth Resolution is the number of pixels (width × height); colour depth is the number of bits per pixel. Bitmap images
Define sample rate and bit depth Sample rate is the number of samples per second (Hz); bit depth is the number of bits per sample. Sound
State the range of values for n bits Unsigned: 0 to 2ⁿ − 1; two's complement: −2ⁿ⁻¹ to 2ⁿ⁻¹ − 1. Limitations of binary representation
Recall the size of each unit 4 bits = 1 nibble, 8 bits = 1 byte, 1024 bytes = 1 KiB, and each larger unit is 1024 of the one before. Units and file size calculations
Define lossless compression File size is reduced without losing any data, so the original can be restored exactly. Lossless and lossy compression (incl. RLE)
Define lossy compression Some data is permanently removed, so the original cannot be restored exactly. Lossless and lossy compression (incl. RLE)
Name the parts of the von Neumann architecture A CPU (control unit, ALU, registers and clock), main memory (RAM), and the address, data and control buses. Stored program concept and von Neumann architecture
Describe the stored program concept Instructions and data are stored together in main memory as binary, and are fetched and executed one at a time. Stored program concept and von Neumann architecture
State the role of each CPU component The CU decodes and controls, the ALU calculates and compares, registers hold values and the clock keeps everything in step. CPU components and the fetch–decode–execute cycle
Put the stages of the cycle in order Fetch, then decode, then execute, repeated for every instruction. CPU components and the fetch–decode–execute cycle
Explain why secondary storage is needed RAM is volatile, so the operating system, programs and files must be kept permanently on non-volatile storage. Main memory and secondary storage
Identify inputs and outputs of an embedded system Inputs are usually sensors and buttons; outputs are motors, heaters, valves, displays and buzzers. Embedded systems
Describe what file management does It organises files in folders, lets them be saved, named, moved and deleted, and controls who can access them. Operating systems
Describe what backup software does It copies files to another device or place so they can be restored if the originals are lost or damaged. Utility software
State what an audit trail records Who did what, and when: for example who changed the code, or who logged in and what they accessed. Robust software: audit trails and code reviews
Give characteristics of low-level languages Specific to one type of processor, give direct control of hardware and memory, and are hard to read. Programming languages and translators
Give characteristics of high-level languages English-like keywords, portable, one statement becomes many machine code instructions, must be translated. Programming languages and translators
Give reasons for connecting computers in a network Sharing resources, sharing files, communicating and managing the computers centrally. LANs, WANs and why computers are connected
State the purpose of an IP address An IP address identifies a device on a network so that data can be delivered to it. The internet: IP addressing and routers
Give advantages and disadvantages of wireless Users can move around and devices are easy to add, but it is slower, has a shorter range and is less secure. Wired and wireless connectivity and performance
Convert between bits and bytes Multiply a number of bytes by 8 to get bits, and divide a number of bits by 8 to get bytes. Network speeds and transmission time
Match protocols to tasks For example, SMTP sends email, FTP transfers files and HTTP requests web pages. Protocols
Match protocols to the layers HTTP, HTTPS, FTP, SMTP, POP3 and IMAP are application; TCP is transport; IP is internet; Ethernet and Wi-Fi are link. The TCP/IP model
Give an advantage and disadvantage of each For example, a bus is cheap, but a break in the backbone stops the whole network. Network topologies
Give impacts of a security breach Data theft, financial loss, fines, damage to reputation and systems being unavailable. Network security and identifying vulnerabilities
Give examples of physical security Locked server rooms, key cards, biometric locks, CCTV and security guards. Protecting networks
Give ways to cut computers' energy use Switch devices off when not in use, use sleep and power-saving settings, and buy energy-efficient hardware. Environmental issues
State why organisations collect personal data To provide a service, personalise it, target adverts, improve products or sell the data to others. Personal data: privacy, ownership, consent and data protection
Describe machine learning A type of AI that learns patterns from training data instead of following rules written for every situation. Artificial intelligence, machine learning and robotics
Describe open-source and proprietary software Open-source code can be viewed, changed and shared; proprietary code is kept secret and its use is restricted. Intellectual property and licensing
Describe the five types of malware Say how each one gets onto a system and what it does once it is there. Malware, social engineering and technical vulnerabilities
Describe common social engineering techniques Phishing, pretexting, baiting, quid pro quo and shoulder surfing. Malware, social engineering and technical vulnerabilities
Encrypt and decrypt with a Caesar cipher Shift each letter a fixed number of places along the alphabet, wrapping round from Z to A. Protecting digital systems and data (incl. encryption)
Describe what an acceptable use policy contains Rules users agree to, such as never sharing passwords or installing software, and the consequences of breaking them. Protecting digital systems and data (incl. encryption)
Make code easier to read and maintain Add comments, meaningful identifiers, indentation and white space without changing what the program does. Developing code: readability, errors, validation and testing
Identify presence, length, range and pattern checks Say which validation check a line of code carries out and why it is needed. Developing code: readability, errors, validation and testing
Write if, elif and else statements Choose between two or more paths using conditions, colons and correct indentation. Sequence, selection and iteration
Use range() to control a for loop Know that range(5) gives 0 to 4 and range(1, 6) gives 1 to 5. Sequence, selection and iteration
Choose a suitable data type for data E.g. real for a price, Boolean for yes or no, string for a phone number. Data types and data structures
Explain the difference between variables and constants A variable's value can change while the program runs; a constant's value cannot. Data types and data structures
Convert input to the correct data type Wrap input() in int() or float() before doing any calculation with it. Input, output and file handling
Use the six relational operators Compare values with ==, !=, <, >, <= and >= to get True or False. Operators
Tell functions and procedures apart A function returns a value; a procedure carries out a task and does not return a value. Subprograms and libraries

Grade 5

Grade 5 checklist (PDF)

Decompose a scenario into sub-problems Break a given system, such as an online booking service, into separate tasks. Decomposition and abstraction
State the benefits of using subprograms Code is written once and called many times, and is easier to test, maintain and share. Decomposition and abstraction
Complete a partly drawn flowchart Fill in missing decisions, processes or outputs so that it does what is described. Flowcharts, pseudocode and program code
Explain the benefits of using constants The value is changed in one place only, and the name makes the code easier to read. Variables, constants and data structures (strings, arrays and records)
Use string length, indexing and concatenation Use len(), word[0] and + to work with strings. Variables, constants and data structures (strings, arrays and records)
Calculate with modulus and integer division 17 // 5 is 3 and 17 % 5 is 2. Arithmetic, relational and logical operators
Combine conditions with AND, OR and NOT Join comparisons to test a range or several conditions at once. Arithmetic, relational and logical operators
Trace selection inside a loop Check the if condition on every pass and only update the variables it changes. Tracing algorithms and trace tables
Identify the type of a given error Decide whether it stops the program running, gives a wrong result or makes it crash. Syntax, logic and runtime errors
Describe how a binary search works Compare with the middle item and discard the half that cannot contain the target. Linear and binary search
Complete a bubble sort and count swaps Show the list after every pass and count the comparisons and swaps. Bubble sort and merge sort
Use test data to check an algorithm Compare the expected result with the actual result for normal, boundary and erroneous data. Efficiency of algorithms
Count passes and comparisons in a bubble sort In the basic version, each pass through a list of n items makes n − 1 comparisons. Efficiency of algorithms
Complete a truth table with three inputs Eight rows, listed in binary counting order from 000 to 111. Truth tables and logic
Find the number of patterns for n bits n bits give 2ⁿ different patterns (states), so 8 bits give 256. Binary representation and unsigned binary–denary conversion
State the 8-bit two's complement range 8-bit two's complement stores whole numbers from −128 to +127. Two's complement
Explain why two's complement is needed Unsigned binary can only store zero and positive numbers; two's complement can also store negative numbers. Two's complement
Add two 8-bit binary numbers Add column by column from the right, carrying 1 into the next column when needed. Binary addition and overflow
Define overflow An overflow happens when a result is too large to be stored in the number of bits available. Binary addition and overflow
State the effect of a shift on value Each place left multiplies an unsigned number by 2; each place right divides it by 2. Logical and arithmetic shifts
Convert 8-bit binary to hexadecimal Split the bits into two nibbles and convert each nibble to one hex digit. Hexadecimal
Convert hexadecimal to 8-bit binary Convert each hex digit to its 4-bit pattern and join the patterns together. Hexadecimal
Work out codes from a given code Letters and digits have consecutive codes, so if 'A' is 65 then 'D' is 68. Characters and ASCII
Calculate the bits needed to store text Multiply the number of characters (including spaces) by 7 for 7-bit ASCII. Characters and ASCII
Find the number of colours A colour depth of n bits gives 2ⁿ colours, e.g. 8 bits give 256. Bitmap images
Encode and decode a simple bitmap Use the given code for each colour to turn the pixels into binary, row by row. Bitmap images
Read sample values from a graph Read the amplitude at each sample time and write it as a binary number. Sound
Find the number of amplitude values A bit depth of n bits gives 2ⁿ possible amplitude values. Sound
Explain why a value cannot be stored A value outside the range needs more bits than are available, so it causes an overflow. Limitations of binary representation
Convert between units Divide by 1024 to go to a larger unit and multiply to go to a smaller one (use 8 between bits and bytes). Units and file size calculations
Choose the right method for a file Lossless for text, program code and spreadsheets; lossy for photos, music and video. Lossless and lossy compression (incl. RLE)
Explain why programs are loaded into RAM The CPU can only fetch instructions directly from main memory, which is also much faster to access than secondary storage. Stored program concept and von Neumann architecture
State what each bus carries, and which way Address bus: addresses, one-way from the CPU; data bus: data and instructions, both ways; control bus: control signals, both ways. CPU components and the fetch–decode–execute cycle
Explain why a higher clock speed helps More clock cycles each second means more instructions can be fetched, decoded and executed each second. CPU components and the fetch–decode–execute cycle
Describe how magnetic and optical storage work Magnetised areas on spinning platters read by a moving head; pits and lands on a disc read by a laser. Main memory and secondary storage
Describe the typical features of embedded systems Dedicated, small, cheap, low power, reliable, with a simple interface and a program kept in non-volatile memory. Embedded systems
Explain the role of a device driver It translates the operating system's general commands into commands that one particular device understands. Operating systems
Describe how user management protects a computer Accounts, passwords and access rights control who can log in and what each user is allowed to do. Operating systems
Describe how anti-malware protects a computer It scans for known malware signatures and suspicious behaviour, then quarantines or deletes threats. Utility software
Explain the benefits of data compression Smaller files take up less storage space and are quicker to send or upload. Utility software
Explain why robust software is important Crashes and vulnerabilities can lose data or money, harm people, and damage an organisation's reputation. Robust software: audit trails and code reviews
Describe how a code review finds vulnerabilities Other programmers check the code line by line for errors and weaknesses before it is released. Robust software: audit trails and code reviews
Explain why low-level languages are used They give direct control of hardware and very efficient code, e.g. for embedded systems and device drivers. Programming languages and translators
Give differences between a LAN and a WAN Compare the area covered and who owns the communication links, e.g. a LAN covers one site and is owned by the organisation. LANs, WANs and why computers are connected
Give disadvantages of a network For example, malware can spread between connected computers, and the equipment and management cost money. LANs, WANs and why computers are connected
Recognise a valid IPv4 address It has exactly four denary numbers, each from 0 to 255, separated by dots, e.g. 81.24.160.3. The internet: IP addressing and routers
Define bandwidth and latency Bandwidth is the maximum amount of data sent per second; latency is the delay before data arrives. Wired and wireless connectivity and performance
Compare copper and fibre-optic cable Fibre is faster, works over longer distances and is not affected by electromagnetic interference, but costs more. Wired and wireless connectivity and performance
Convert between kilobits, megabits and gigabits Multiply or divide by 1000 for each step, e.g. 3 Mbps = 3,000,000 bits per second. Network speeds and transmission time
Calculate time from file size and rate Use time = file size ÷ transmission rate, with the file size and the rate in matching units. Network speeds and transmission time
Explain why protocols are needed Devices from different manufacturers must follow the same rules to understand the data they exchange. Protocols
Explain why HTTPS is used It encrypts data sent between a browser and a web server, so intercepted data cannot be read. Protocols
Describe the role of each layer Say what each layer does to the data, e.g. the internet layer adds IP addresses and routes packets. The TCP/IP model
Describe how data travels in each topology Bus: along the backbone to every device; star: through the switch to one device; mesh: by one of several routes. Network topologies
Define penetration testing and ethical hacking Both are authorised attempts to find weaknesses in a system so that they can be fixed. Network security and identifying vulnerabilities
Explain how access control protects a network Usernames, passwords and access levels mean only authorised users can reach only the data they need. Protecting networks
Define two-factor authentication Proving your identity in two different ways, e.g. a password plus a code sent to your phone. Protecting networks
Explain the harm caused by e-waste Toxic substances such as lead and mercury can leak from landfill into soil and water, and valuable metals are wasted. Environmental issues
Explain why data centres use so much energy Thousands of servers run 24 hours a day and must be kept cool, often using electricity generated from fossil fuels. Environmental issues
Explain how computers can help the environment For example, video calls cut travel, smart meters help people use less energy and sensors monitor pollution. Environmental issues
Explain privacy and consent issues in context Say who could see or use the data, whether the person agreed, and what harm could follow. Personal data: privacy, ownership, consent and data protection
Describe what data protection law requires Data must be used openly and only for its stated purpose, limited to what is needed, accurate, not kept too long and secure. Personal data: privacy, ownership, consent and data protection
Explain how algorithmic bias happens If the training data is unrepresentative or reflects past prejudice, the system learns to treat some groups unfairly. Artificial intelligence, machine learning and robotics
Explain differences between copyright and patents Copyright is automatic and protects original work; a patent must be applied for and protects an invention. Intellectual property and licensing
Explain how viruses differ from worms A virus needs a host file and a user action to spread; a worm spreads itself across networks. Malware, social engineering and technical vulnerabilities
Explain how anti-malware and encryption protect data Anti-malware detects and removes malware; encryption makes stolen or intercepted data unreadable without the key. Protecting digital systems and data (incl. encryption)
Choose normal, boundary and erroneous test data Pick actual values for a test plan and give the expected result of each test. Developing code: readability, errors, validation and testing
Choose count- or condition-controlled loops Use for when the number of repeats is known and while when it depends on a condition. Sequence, selection and iteration
Trace loops to find the output Use a trace table to follow each variable through every pass of a loop. Sequence, selection and iteration
Convert between data types by casting Use int(), float() and str() before calculating or joining text. Data types and data structures
Access and change items in a list Use an index that starts at 0, len() to count items and append() to add one. Data types and data structures
Open a file in the right mode Use "r" to read, "w" to write a new file and "a" to add to the end of a file. Input, output and file handling
Read and split a CSV file Loop through the lines, strip the newline and split each line at the commas. Input, output and file handling
Use integer division and modulus 17 // 5 gives 3 (the whole number part) and 17 % 5 gives 2 (the remainder). Operators
Combine conditions with and, or, not E.g. age >= 13 and age <= 19 is True only for ages 13 to 19. Operators
Import and use library subprograms E.g. import random, then use random.randint(1, 6) for a dice roll. Subprograms and libraries
Give benefits of using subprograms Code can be reused, tested on its own and is easier to read and maintain. Subprograms and libraries

Grade 6

Grade 6 checklist (PDF)

Apply abstraction to a real-world model Say which details a model must keep and which it can leave out, linked to its purpose. Decomposition and abstraction
Compare count-controlled and condition-controlled loops A count-controlled loop repeats a set number of times; a condition-controlled loop repeats while a condition is True. Flowcharts, pseudocode and program code
Use a two-dimensional array Find or change an item using a row index and then a column index. Variables, constants and data structures (strings, arrays and records)
Apply operator precedence to evaluate expressions Brackets first, then exponentiation, then multiplication and division, then addition and subtraction. Arithmetic, relational and logical operators
Trace algorithms that use arrays or strings Use the index on each pass to find the correct item or character. Tracing algorithms and trace tables
Find a logic error using test data Compare the expected result with the actual result, then trace to find the line. Syntax, logic and runtime errors
Show the stages of a binary search Give each middle item checked and the part of the list that is left. Linear and binary search
Describe how a merge sort works Split the list into single items, then merge pairs of sorted lists until one list is left. Bubble sort and merge sort
Show the stages of a merge sort Write the lists after each split and after each round of merging. Bubble sort and merge sort
Find maximum comparisons for a binary search Find the smallest power of 2 that is greater than the number of items. Efficiency of algorithms
Use working columns for brackets and NOT Work out each part of the statement in its own column before the output. Truth tables and logic
Find the largest unsigned value for n bits The largest value is 2ⁿ − 1, because one of the patterns is used for 0. Binary representation and unsigned binary–denary conversion
Convert two's complement binary to denary Treat the MSB as −128 and add the place values of the other 1s. Two's complement
Convert negative denary to two's complement Write the positive number in 8 bits, invert every bit, then add 1. Two's complement
Spot an overflow in an 8-bit addition A 1 carried out of the most significant bit means the result needs 9 bits. Binary addition and overflow
Apply an arithmetic shift right Move every bit right and fill the gaps on the left with copies of the sign bit (the MSB). Logical and arithmetic shifts
Explain why hexadecimal is used It is shorter and easier for people to read, remember and copy than binary, and it converts to binary easily. Hexadecimal
Convert between binary codes and characters Convert the 7-bit code to denary, then count on or back from a code you know. Characters and ASCII
Explain effects of changing resolution or colour depth More pixels or more bits per pixel improve quality but increase the file size. Bitmap images
Calculate the sample interval Sample interval = 1 ÷ sample rate: the time between one sample and the next. Sound
Explain effects of sample rate and bit depth Increasing either makes the recording a closer copy of the original, but makes the file larger. Sound
Explain the limits of colour and bit depth Few bits give few colours or amplitude values, so detail is lost or values are rounded. Limitations of binary representation
Explain the limits of a character set 7-bit ASCII has only 128 codes, so it cannot represent every character in every language. Limitations of binary representation
Explain why storage uses multiples of 1024 1024 = 2¹⁰, a power of 2, which suits binary computers. Units and file size calculations
Construct an expression for a file size Build it stage by stage: size in bits, then ÷ 8, then ÷ 1024 for each unit. Units and file size calculations
Encode and decode data using RLE Replace each run of a repeated value with a count and the value, e.g. 5A. Lossless and lossy compression (incl. RLE)
Explain why new tasks need no rewiring A different program is simply loaded into memory, and the CPU executes whatever instructions are stored there. Stored program concept and von Neumann architecture
Describe the fetch stage step by step Address out on the address bus, read signal on the control bus, instruction back on the data bus, program counter incremented. CPU components and the fetch–decode–execute cycle
Describe how solid-state storage works Flash memory cells trap an electrical charge (or not) to store 1s and 0s, with no moving parts. Main memory and secondary storage
Compare storage by capacity, speed, cost, durability For example, an SSD is faster and tougher than a hard disk drive but costs more per GiB. Main memory and secondary storage
Compare embedded and general-purpose computers One task with a fixed program, compared with many tasks and software the user can install. Embedded systems
Explain how multitasking works on one processor The OS gives each process a short time slice in turn, switching so fast that they seem to run at the same time. Operating systems
Explain how defragmentation speeds up a hard disk It puts the fragments of each file back together, so the read/write head moves less. Utility software
Explain how audit trails help find problems They show which change caused a fault, or reveal unusual activity that suggests an attack. Robust software: audit trails and code reviews
Describe how a compiler translates code It translates the whole program into machine code before it runs, producing an executable file. Programming languages and translators
Describe how an interpreter translates code It translates and runs one line at a time, every time the program runs, and stops at the first error. Programming languages and translators
Explain benefits of a network in context Link each benefit to the scenario, e.g. records stored on a server can be opened from every computer in the building. LANs, WANs and why computers are connected
Describe how routers forward packets Each router reads a packet's destination IP address and sends the packet on towards the destination network. The internet: IP addressing and routers
Convert an IPv4 address to binary Convert each of the four numbers to an 8-bit binary number, keeping any leading zeros. The internet: IP addressing and routers
Compare IPv4 and IPv6 addresses IPv4 uses 32 bits written as four denary numbers; IPv6 uses 128 bits written as groups of hexadecimal digits. The internet: IP addressing and routers
Explain why Wi-Fi performance falls Distance, walls, interference and sharing the bandwidth between many devices all reduce performance. Wired and wireless connectivity and performance
Construct an expression for transmission time For example, 20 × 1024 × 1024 × 8 ÷ (40 × 1,000,000) seconds for a 20 MiB file at 40 Mbps. Network speeds and transmission time
Compare POP3 and IMAP POP3 downloads emails to one device; IMAP keeps them on the server so that every device shows the same emails. Protocols
Explain benefits of a layered model Layers are independent, so one can change without affecting the others, and standards let products from different makers work together. The TCP/IP model
Compare the reliability of the topologies Explain what stops working when a cable or a central device fails in each topology. Network topologies
Explain why organisations use penetration testing To find vulnerabilities before criminals exploit them, so that they can be fixed. Network security and identifying vulnerabilities
Distinguish ethical hacking from malicious hacking Ethical hackers have permission and report what they find; malicious hackers have no permission and aim to cause harm. Network security and identifying vulnerabilities
Explain how a firewall works It checks each packet against rules (e.g. IP addresses and port numbers) and blocks packets that break them. Protecting networks
Explain the effect of short replacement cycles Replacing devices more often means more are manufactured (materials, energy, emissions) and more become e-waste. Environmental issues
Explain misuse and the effects of breaches Misuse and breaches can lead to fraud or identity theft for people, and fines and lost trust for organisations. Personal data: privacy, ownership, consent and data protection
Explain safety risks of autonomous machines A self-driving car or robot that makes a wrong decision, meets a new situation or is hacked can injure people. Artificial intelligence, machine learning and robotics
Explain pros and cons of open source Usually free, customisable and community-supported, but may have no official support or guaranteed updates. Intellectual property and licensing
Explain how unpatched software is exploited Attackers use known, published security flaws that have not been fixed on that computer. Malware, social engineering and technical vulnerabilities
Spot and explain signs of phishing Urgency, an unexpected request, a generic greeting and a link to the wrong web address. Malware, social engineering and technical vulnerabilities
Describe a backup and recovery procedure Regular automatic backups kept off site and offline, several versions, tested restores and a recovery plan. Protecting digital systems and data (incl. encryption)
Locate and correct errors in a program Find the line with the error, name the type of error and write the corrected line. Developing code: readability, errors, validation and testing
Convert a flowchart or pseudocode into Python Turn each input, process, decision and output of an algorithm into the matching Python statement. Developing code: readability, errors, validation and testing
Iterate over every item of a data structure Use for item in a list, or for character in a string, to process each one in turn. Sequence, selection and iteration
Find length, position, substrings and case Use len(), find(), slicing such as word[1:4], upper() and lower(). Data types and data structures
Write records to a text file Build each record as one string with commas and a newline, then close the file. Input, output and file handling
Apply the order of operations Brackets first, then exponentiation, then *, /, // and %, then + and −. Operators
Write a procedure that takes parameters Define it with def, pass values in when you call it, and let it carry out its task. Subprograms and libraries

Grade 7

Grade 7 checklist (PDF)

Explain benefits in the context given Link each benefit to the scenario with a clear consequence, e.g. '... so the app is finished sooner'. Decomposition and abstraction
Write an algorithm using selection and repetition For example, a loop that keeps asking for an input until the value is valid. Flowcharts, pseudocode and program code
Choose between an array and a record A record holds related fields of different types; an array holds items of the same type. Variables, constants and data structures (strings, arrays and records)
Use modulus and integer division to solve problems E.g. test whether a number is even, or convert minutes into hours and minutes. Arithmetic, relational and logical operators
State the purpose of an algorithm Spot the pattern in the trace, e.g. 'it adds up the digits of a number'. Tracing algorithms and trace tables
Correct logic errors in an algorithm Give the line number, what is wrong and the corrected code. Syntax, logic and runtime errors
Compare linear and binary search Weigh speed on large lists against simplicity and working on unsorted data. Linear and binary search
Compare bubble sort and merge sort Weigh speed on large lists against memory use and simplicity. Bubble sort and merge sort
Explain improvements to a bubble sort Stop after a pass with no swaps, and skip the items already in place. Bubble sort and merge sort
Suggest how to make an algorithm more efficient E.g. stop a loop as soon as the answer is known. Efficiency of algorithms
Explain why an algorithm is not fit for purpose Use test data to show a case where it gives the wrong result. Efficiency of algorithms
Write a logic statement from a description Turn a rule such as 'on if A and not B, or if C' into a statement. Truth tables and logic
Work out the minimum bits for a requirement Find the smallest power of 2 that is at least the number of different values needed. Binary representation and unsigned binary–denary conversion
Explain the effect of an overflow The carried-out bit is lost, so the stored result is wrong (256 less than the true total for 8 bits). Binary addition and overflow
Explain loss of precision in a right shift Bits shifted off the right-hand end are lost, so an answer that should have a fraction is rounded down. Logical and arithmetic shifts
Explain overflow in a left shift A 1 shifted off the left-hand end is lost, so the result is wrong because it is too big for 8 bits. Logical and arithmetic shifts
Convert longer binary and hex values Group the bits in fours from the right: each group is one hex digit, so 16 bits are 4 hex digits. Hexadecimal
Explain the limitations of 7-bit ASCII 128 codes cannot include accented letters, other alphabets or most symbols and emoji. Characters and ASCII
Construct a file size expression for an image width × height × colour depth gives bits; ÷ 8 for bytes, then ÷ 1024 for KiB. Bitmap images
Construct a file size expression for sound sample rate × bit depth × duration in seconds gives the size in bits. Sound
Explain precision limits when storing measurements A fixed number of bits gives fixed steps, so values between the steps have to be rounded. Limitations of binary representation
Calculate the total storage for several files Convert every size to the same unit before adding or multiplying. Units and file size calculations
Explain when RLE works well RLE only saves space when the data has long runs of the same value. Lossless and lossy compression (incl. RLE)
Explain how a jump changes sequential execution Instructions normally run in the order they are stored, but a jump puts a new address in the program counter, so instructions can be repeated or skipped. Stored program concept and von Neumann architecture
Describe decoding and executing a given instruction Say how the CU decodes it, which bus carries what, and what the ALU or memory does with it. CPU components and the fetch–decode–execute cycle
Calculate addressable memory from address bus width An n-bit address bus can address 2ⁿ memory locations. CPU components and the fetch–decode–execute cycle
Explain why a feature matters in context For example, a pacemaker must use very little power because its battery is inside the patient's body. Embedded systems
Apply the four functions to a scenario Work out which function each part of a scenario needs, and describe it using the scenario's details. Operating systems
Compare full and incremental backups Incremental backups are quicker and smaller, but restoring needs the full backup plus every incremental one since. Utility software
Spot vulnerabilities in a piece of code Look for unvalidated input, passwords written into the code and unlimited log-in attempts, and suggest a fix for each. Robust software: audit trails and code reviews
Choose a suitable translator for a situation An interpreter suits writing and testing; a compiler suits a finished program given to users. Programming languages and translators
Discuss whether an organisation should use a network Weigh the benefits against the costs, security risks and reliance on central devices, then reach a justified conclusion. LANs, WANs and why computers are connected
Explain why IPv6 was introduced 32-bit IPv4 allows only about 4.3 billion addresses, which is not enough for all the devices now online. The internet: IP addressing and routers
Recommend a connection type with justification Match speed, range, latency, mobility, security and cost to the needs of the users in the scenario. Wired and wireless connectivity and performance
Rearrange the formula for size or rate Use file size = transmission rate × time, or transmission rate = file size ÷ time. Network speeds and transmission time
Explain why real transfers take longer Shared bandwidth, interference, packet headers and resent packets all add to the time taken. Network speeds and transmission time
Describe the roles of TCP and IP TCP splits data into numbered packets and makes sure they all arrive in order; IP addresses and routes the packets. Protocols
Describe how data passes through the layers Down the layers on the sender, with each adding a header, then up the layers on the receiver, with each removing one. The TCP/IP model
Calculate the cables needed for a full mesh A full mesh of n devices needs n(n − 1) ÷ 2 cables, e.g. 6 devices need 15. Network topologies
Describe the stages of a penetration test Agree the scope and get permission, gather information, attempt attacks, report, then fix and retest. Network security and identifying vulnerabilities
Interpret a table of firewall rules Apply the rules in order to decide whether each packet is allowed or blocked. Protecting networks
Explain why 'anonymous' data may identify people Combining details such as postcode, date of birth and location can point to one person. Personal data: privacy, ownership, consent and data protection
Explain accountability and legal liability problems It is hard to say who is to blame, or who must pay, when a machine made the decision itself. Artificial intelligence, machine learning and robotics
Explain what a licence allows in context Work out whether the code may be changed, sold or shared, and whether changes must be released too. Intellectual property and licensing
Explain why social engineering beats technical defences A genuine user hands over access, so firewalls, encryption and passwords are bypassed. Malware, social engineering and technical vulnerabilities
Explain the limits of each protection method For example, encryption does not stop data being deleted or locked by ransomware, so backups are still needed. Protecting digital systems and data (incl. encryption)
Write validation and authentication code Repeat an input until it passes every check, and check an ID and password against stored data. Developing code: readability, errors, validation and testing
Use nested loops and nested selection Put a loop or if inside another and work out how many times the inner block runs. Sequence, selection and iteration
Use a two-dimensional list Access an item with name[row][column] and use nested loops to process every item. Data types and data structures
Code a validation loop for user input Keep asking until the input passes every check, showing a helpful message each time. Input, output and file handling
Use modulus to test divisibility n % 2 == 0 tests for an even number; n % 10 gives the last digit. Operators
Write a function that returns a value Take parameters, calculate a result, return it and use the returned value in the main program. Subprograms and libraries

Grade 8

Grade 8 checklist (PDF)

Convert between flowcharts, pseudocode and code Turn a flowchart into Python, or Python into a flowchart, keeping exactly the same logic. Flowcharts, pseudocode and program code
Process arrays and records with loops Loop through every item or record to total, count, search or output fields. Variables, constants and data structures (strings, arrays and records)
Write complex conditions with brackets and NOT Build conditions such as not (x == 0 or y == 0) that do exactly what is needed. Arithmetic, relational and logical operators
Trace nested loops and 2D arrays accurately Keep track of both loop counters as the inner loop runs in full on each pass of the outer loop. Tracing algorithms and trace tables
Explain how to prevent runtime errors E.g. check that a divisor is not zero, or that an index is in range, before using it. Syntax, logic and runtime errors
Write code for a linear search Use a loop, a comparison and a flag that stops the search when the item is found. Linear and binary search
Write code for a bubble sort Nested loops that compare adjacent items, swap them with a temporary variable and use a flag. Bubble sort and merge sort
Evaluate algorithms by time and memory Judge which algorithm suits a scenario, using compares, passes and memory use. Efficiency of algorithms
Use a truth table to solve a problem Find the input combinations that give a required output. Truth tables and logic
Explain how one pattern has different meanings The bits have no meaning on their own: the program using them decides whether they are a number, a character, a colour or an instruction. Binary representation and unsigned binary–denary conversion
Find the range for any number of bits n bits store −2ⁿ⁻¹ to 2ⁿ⁻¹ − 1, e.g. 4 bits store −8 to +7. Two's complement
Compare a pattern's unsigned and signed values When the MSB is 1, the unsigned value is 256 more than the two's complement value, because that bit is worth +128 instead of −128. Two's complement
Explain why arithmetic shifts suit signed numbers Copying the sign bit keeps a negative number negative, so it is correctly divided by 2 for each place. Logical and arithmetic shifts
Explain that hex does not save memory The computer still stores the value in binary; hex is only the way it is shown to people. Hexadecimal
Explain why '7' and 7 are stored differently The character '7' is stored as its ASCII code, 55 (011 0111), not as the binary number 7 (000 0111). Characters and ASCII
Work backwards to find colour depth Colour depth = total bits ÷ number of pixels, after converting the size into bits. Bitmap images
Calculate the minimum bits for a requirement Find the smallest power of 2 that covers every value needed. Limitations of binary representation
Solve multi-step storage capacity problems Number of files that fit = capacity ÷ size of one file, in the same unit, rounded down. Units and file size calculations
Evaluate compression methods for a scenario Weigh file size and speed against quality and whether the data must be exact. Lossless and lossy compression (incl. RLE)
Explain a drawback of one shared memory Instructions and data travel on the same buses, so they cannot be fetched at the same time and the CPU may have to wait. Stored program concept and von Neumann architecture
Justify a storage choice for a scenario Weigh the user's needs against the features of each type of storage and reach a reasoned conclusion. Main memory and secondary storage
Explain why SSDs should not be defragmented Access time does not depend on where data is stored, and the extra writing wears out the flash memory. Utility software
Evaluate ways of making software robust Weigh code reviews, audit trails and testing against their cost and the fact that none of them can find every problem. Robust software: audit trails and code reviews
Explain why the internet survives link failures There are many routes and no central point, so routers send packets around a failed link or router. The internet: IP addressing and routers
Discuss wired versus wireless for a scenario Weigh up both types for each group of users and reach a justified recommendation, often a mixture of both. Wired and wireless connectivity and performance
Explain which protocols a scenario uses Name the protocol for each stage and justify it, e.g. HTTPS for a payment and IMAP for reading email on several devices. Protocols
Apply the model to an unfamiliar situation For example, switching from Ethernet to Wi-Fi changes only the link layer, so the web browser is unaffected. The TCP/IP model
Recommend a topology for a scenario Balance cost, performance, fault tolerance and ease of expansion, and justify the choice. Network topologies
Evaluate the limits of penetration testing A test is a snapshot of one moment, so new vulnerabilities appear afterwards and testing must be repeated. Network security and identifying vulnerabilities
Evaluate a combination of protection methods Explain why no single method is enough and how the three methods cover each other's gaps. Protecting networks
Weigh up a technology's overall environmental impact In a 6-mark answer, balance the harms against the benefits in the given context and reach a justified conclusion. Environmental issues
Discuss the benefits and risks of collecting data Balance convenience and better services against privacy, consent and security, then reach a conclusion. Personal data: privacy, ownership, consent and data protection
Discuss using AI in a given context Weigh benefits such as speed and consistency against safety, bias, accountability and liability, then conclude. Artificial intelligence, machine learning and robotics
Discuss open-source versus proprietary for a user Weigh cost, income, support, customisation and control for the person or organisation, then recommend one. Intellectual property and licensing
Discuss the threats facing an organisation Link each threat to the organisation's systems and data, and explain the likely impact. Malware, social engineering and technical vulnerabilities
Discuss how an organisation should protect data Recommend layered measures that fit the organisation's data, threats and budget, with reasons. Protecting digital systems and data (incl. encryption)
Evaluate fitness for purpose and efficiency Use test results and the number of comparisons, loop passes and memory used to judge a program. Developing code: readability, errors, validation and testing
Combine constructs to solve unfamiliar problems Decompose the task, choose the right constructs and give each loop a single exit point. Sequence, selection and iteration
Store and process records in a list Hold each record as an inner list of fields and loop through the records to search or total them. Data types and data structures
Code authentication using an ID lookup Search the stored IDs for a match and check the password stored with that ID. Input, output and file handling
Evaluate complex Boolean expressions Know that Python applies not first, then and, then or, and use brackets to control the order. Operators
Explain local and global variables Say where each variable can be used and why local variables are better practice. Subprograms and libraries

Grade 9

Grade 9 checklist (PDF)

Explain overflow when adding two's complement numbers Two positive numbers with a total above +127 give a pattern with an MSB of 1, which reads as negative. Binary addition and overflow
Evaluate trade-offs between bits, quality and size More bits give more range or precision but need more storage and take longer to transmit. Limitations of binary representation

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