OCR 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)

State the purpose of the CPU The CPU carries out the fetch–execute cycle: it fetches, decodes and executes instructions, over and over, to run programs. Architecture of the CPU
Name the three characteristics affecting performance Clock speed, cache size and number of cores. CPU performance
Define an embedded system A computer system inside a larger device that carries out a dedicated function. Embedded systems
Give examples of embedded systems E.g. the controller in a washing machine or microwave, a smart thermostat, or a car's engine management system. Embedded systems
Define volatile and non-volatile memory Volatile memory loses its contents when the power is turned off; non-volatile memory keeps them. Primary storage (RAM, ROM, cache, virtual memory)
Explain why secondary storage is needed It is non-volatile, so programs and files are kept when the power is off. Secondary storage
Give examples of each type of storage Magnetic: HDD, tape; optical: CD, DVD, Blu-ray; solid state: SSD, USB flash drive, SD card. Secondary storage
Explain why data is stored in binary Computers are made of switches (transistors) with two states, on and off, represented by 1 and 0. Units and capacity
Put the units in order Bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte, petabyte. Units and capacity
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, denary and hexadecimal
Define a character set The set of characters a computer can represent, each with its own unique binary code. Characters: ASCII and Unicode
Define pixel, colour depth and resolution A pixel is a single dot of colour; colour depth is the number of bits per pixel; resolution is the number of pixels. Images
Describe how sound is sampled The amplitude of the sound wave is measured at regular intervals and each measurement is stored in binary. Sound
State why files are compressed To make files smaller, so they take up less storage space and are quicker to send. Compression
State what LAN and WAN stand for Local Area Network and Wide Area Network. LANs, WANs and network performance
State the role of a server A server provides services or resources, such as files, printing, email or web pages, to clients. Client–server and peer-to-peer
State the role of a client A client requests services or resources from a server. Client–server and peer-to-peer
Name the hardware needed for a LAN NIC, switch, router, wireless access point and transmission media. Network hardware
Define the Internet The Internet is a worldwide collection of interconnected computer networks. The Internet, DNS, hosting and the cloud
Identify a star or mesh network diagram Star: all devices connected to one central device. Mesh: devices connected to several other devices. Star and mesh topologies
Give examples of wired and wireless connections Ethernet is wired; Wi-Fi and Bluetooth are wireless. Ethernet, Wi-Fi and Bluetooth
Define encryption Scrambling data using an algorithm and a key so it cannot be understood without the key. Encryption
Recognise IPv4, IPv6 and MAC addresses IPv4: four denary numbers with dots; IPv6: groups of hex digits with colons; MAC: six pairs of hex digits. IP and MAC addressing
Define a protocol A set of rules for how devices communicate and transfer data. Standards and common protocols
Name the main threats to computer systems Malware, social engineering, brute-force attacks, denial of service, data interception and theft, SQL injection. Threats to computer systems and networks
Name methods to protect a network Penetration testing, anti-malware, firewalls, user access levels, passwords, encryption and physical security. Identifying and preventing vulnerabilities
State the purpose of an operating system It manages the hardware and software, and provides a user interface and a platform for applications. Operating systems
State the purpose of utility software To maintain, protect or optimise the computer system. Utility software
Give examples of each type of issue E.g. job losses (ethical), social media (cultural), e-waste (environmental), location tracking (privacy). Ethical, cultural, environmental and privacy issues
Name the three main computing laws Data Protection Act 2018, Computer Misuse Act 1990, and Copyright, Designs and Patents Act 1988. Legislation
Define open source and proprietary software Open source: source code available to view, modify and share. Proprietary: source code closed; the licence restricts use. Open source and proprietary software
Define abstraction Abstraction is removing unnecessary detail so you can focus on the parts of a problem that matter. Computational thinking
Define decomposition Decomposition is breaking a problem down into smaller sub-problems that are easier to solve. Computational thinking
Identify the inputs and outputs of a problem Pick out the data that goes in and the results that come out of a described program. Inputs, processes, outputs and structure diagrams
Name the flowchart symbols Terminal, input/output, process, decision and sub program symbols, joined by arrows. Pseudocode and flowcharts
Define syntax error and logic error A syntax error breaks the rules of the language; a logic error runs but gives the wrong result. Trace tables and common errors
Describe how a linear search works Check each item in turn from the start until the item is found or the end is reached. Linear and binary search
State what a bubble sort does It sorts a list by comparing adjacent items and swapping them if they are out of order. Bubble sort
State what an insertion sort does It takes each item in turn and inserts it into the correct place in a sorted part of the list. Insertion sort
Define a variable and a constant A variable's value can change while the program runs; a constant's value cannot. Variables, constants, input, output and assignment
Name the three programming constructs Sequence (in order), selection (decisions) and iteration (repetition). Sequence, selection and iteration
Use the basic arithmetic operators Add, subtract, multiply and divide with +, −, * and /. Arithmetic, comparison and Boolean operators
Name the five data types Integer, real, Boolean, character and string. Data types and casting
Name types of validation check Range, type, length, presence and format checks. Defensive design
State the purpose of testing To find and fix errors, and check the program meets its requirements. Testing
Recall the truth tables for AND, OR, NOT AND needs both inputs 1; OR needs at least one; NOT reverses the input. Logic gates, diagrams and truth tables
Give examples of high-level and low-level languages Python and Java are high level; machine code and assembly language are low level. Languages and translators
State what an IDE is Software with tools to help programmers write, run and debug programs. The Integrated Development Environment

Grade 4

Grade 4 checklist (PDF)

Describe what the ALU and CU do The ALU carries out arithmetic and logical operations; the CU decodes instructions and sends control signals to coordinate the other components. Architecture of the CPU
Name the four Von Neumann registers Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR) and Accumulator (ACC). Architecture of the CPU
State what clock speed measures The number of fetch–execute cycles carried out per second, e.g. 3.5 GHz means 3.5 billion cycles per second. CPU performance
State the characteristics of embedded systems Dedicated function, small, low power, low cost, reliable, with the program usually stored in ROM. Embedded systems
State the purpose of RAM and ROM RAM holds the programs and data currently in use; ROM holds the start-up (boot) instructions. Primary storage (RAM, ROM, cache, virtual memory)
Explain why computers need primary storage The CPU can only access instructions and data directly from primary storage, which is much faster than secondary storage. Primary storage (RAM, ROM, cache, virtual memory)
Define the six storage characteristics Capacity, speed, portability, durability, reliability and cost, and what each one means. Secondary storage
Convert between units of data Multiply by 1000 to change to a smaller unit and divide by 1000 to change to a larger one (use 8 between bits and bytes). Units and capacity
Convert denary to 8-bit binary Work from 128 downwards, putting a 1 in each column whose value you can subtract. Binary, denary and hexadecimal
Identify the most and least significant bits The most significant bit is the left-most bit (worth 128 in 8 bits); the least significant bit is the right-most (worth 1). Binary, denary and hexadecimal
Apply the four binary addition rules 0 + 0 = 0, 0 + 1 = 1, 1 + 1 = 10 (write 0, carry 1), 1 + 1 + 1 = 11 (write 1, carry 1). Binary addition, overflow and shifts
State how many characters ASCII represents ASCII uses 7 bits (128 characters); extended ASCII uses 8 bits (256 characters). Characters: ASCII and Unicode
Represent a simple image in binary With 1 bit per pixel, e.g. 1 = black and 0 = white, each row of pixels becomes a row of bits. Images
Define sample rate and bit depth Sample rate is the number of samples taken per second (Hz); bit depth is the number of bits used for each sample. Sound
Define lossy and lossless compression Lossy permanently removes some data; lossless reduces the file size without losing any data. Compression
Describe the differences between a LAN and WAN A LAN covers a small area such as one site and uses hardware the organisation owns; a WAN covers a large area and uses infrastructure owned by other organisations. LANs, WANs and network performance
Name factors that affect network performance Bandwidth, number of users, transmission media, error rate, latency and interference. LANs, WANs and network performance
Describe a peer-to-peer network All computers have equal status and share resources directly with each other, with no central server. Client–server and peer-to-peer
State the purpose of each device E.g. a WAP lets wireless devices join a wired network; a router connects the LAN to the Internet. Network hardware
Explain why DNS is needed People remember domain names easily, but computers need IP addresses to send data to the right server. The Internet, DNS, hosting and the cloud
Explain what web hosting is Storing a website's files on a server connected to the Internet so that users can access the website. The Internet, DNS, hosting and the cloud
Draw a star or mesh topology Draw each device linked to a labelled central switch, or linked to several other devices. Star and mesh topologies
State benefits of wired and wireless connections Wired: faster, more reliable and more secure. Wireless: mobility, no cables, easy to add devices. Ethernet, Wi-Fi and Bluetooth
Use plaintext, ciphertext and key correctly Plaintext is the original data, ciphertext is the encrypted data, and the key is used to encrypt and decrypt. Encryption
State who assigns IP and MAC addresses The network assigns the IP address; the manufacturer assigns the MAC address to the NIC. IP and MAC addressing
State the purpose of each common protocol HTTP/HTTPS: web pages; FTP: files; SMTP: sending email; POP/IMAP: retrieving email; TCP/IP: packets and routing. Standards and common protocols
Explain why standards are needed Agreed rules let hardware and software from different manufacturers work together. Standards and common protocols
Describe what a layer is A division of network communication with a specific job, which uses the layer below and serves the layer above. The concept of layers
Identify an attack from a description E.g. flooding a server with requests so users cannot reach it is a denial of service attack. Threats to computer systems and networks
Describe features of a strong password Long, a mix of upper and lower case letters, numbers and symbols, and not a word or a personal detail. Identifying and preventing vulnerabilities
Identify the functions of an operating system User interface, memory management and multitasking, peripheral management, user management, file management. Operating systems
Name three types of utility software Encryption software, defragmentation software and data compression software. Utility software
Define the digital divide and its causes The gap between people with and without access to technology, caused by cost, location, age, skills or disability. Ethical, cultural, environmental and privacy issues
State what each law protects Personal data (DPA), computer systems and data from unauthorised access (CMA), original work (CDPA). Legislation
Give examples of each type E.g. Linux and LibreOffice (open source); Microsoft Windows and Adobe Photoshop (proprietary). Open source and proprietary software
Define algorithmic thinking Algorithmic thinking is working out the steps needed to solve a problem and the order they must happen in. Computational thinking
Identify the processes in a problem Name what the program does with the data, such as calculating, checking or sorting. Inputs, processes, outputs and structure diagrams
Describe what a structure diagram shows It shows a problem broken down into smaller sub-problems as a hierarchy of boxes. Inputs, processes, outputs and structure diagrams
Follow a flowchart or pseudocode to find outputs Work through each step with given inputs, following the correct branch at each decision. Pseudocode and flowcharts
Spot a syntax error in code Find missing brackets, missing quotation marks or misspelt keywords, and correct them. Trace tables and common errors
State the condition needed for binary search The data must already be sorted, in ascending or alphabetical order. Linear and binary search
Show the list after one pass Compare each adjacent pair from left to right, swapping where needed. Bubble sort
Describe the splitting stage of merge sort The list is repeatedly divided in half until every sub-list contains one item. Merge sort
Identify variables, constants and assignments in code Point to the lines that declare a constant, assign a value, take input or give output. Variables, constants, input, output and assignment
Explain why a constant is used It cannot be changed by mistake, and it only needs updating in one place in the code. Variables, constants, input, output and assignment
Identify each construct in given code Point to the lines that use if or switch, and the lines that use a loop. Sequence, selection and iteration
Use the comparison operators correctly Use ==, !=, <, <=, > and >= to compare values and give True or False. Arithmetic, comparison and Boolean operators
Choose a suitable data type for data For example a price is real, a count is integer and a yes/no value is Boolean. Data types and casting
Join strings together (concatenation) Use + to join strings, casting numbers with str() first. String manipulation
Explain why programs store data in files Data in variables is lost when the program ends; a file keeps it for next time. File handling
Access an array element by its index Remember the first element is at index 0, so names[2] is the third item. Arrays and records
Identify records and fields in a table Each row is a record; each column is a field. SQL
Describe what a sub program is A named block of code that does a specific task and can be called when needed. Functions and procedures
State the range of values random() can give random(1, 6) gives a whole number from 1 to 6 inclusive. Random number generation
Choose a suitable validation check Match the check to the data, such as a range check for an age. Defensive design
Give examples of each type of test data Normal, boundary, invalid and erroneous data for a given rule. Testing
Recognise the symbols for the three gates AND is D-shaped, OR has a curved back and a point, NOT is a triangle with a circle. Logic gates, diagrams and truth tables
Explain why translators are needed The CPU can only execute machine code, so source code must be translated. Languages and translators
Name the main tools in an IDE Editor, error diagnostics, run-time environment and translator. The Integrated Development Environment
Identify inputs, processes and outputs for a scenario Pick out the data in, what is done with it and what comes out. Paper 2 Section B practice: design, write, test and refine

Grade 5

Grade 5 checklist (PDF)

Know which registers hold data or addresses The PC and MAR hold addresses; the MDR holds data or an instruction; the accumulator holds data (the results of calculations). Architecture of the CPU
Explain how each characteristic improves performance Link each one to more instructions processed per second or less time waiting for RAM. CPU performance
Explain why a device uses an embedded system Link each characteristic to the device, e.g. low power, so a fitness tracker's battery lasts for days. Embedded systems
Compare RAM and ROM RAM is volatile and can be read from and written to; ROM is non-volatile and read-only. Primary storage (RAM, ROM, cache, virtual memory)
Compare HDDs and SSDs SSDs are faster, more durable and use less power; HDDs are cheaper per GB and available with larger capacities. Secondary storage
Calculate the storage needed for several files Convert every file size to the same unit, add them up and compare the total with a device's capacity. Units and capacity
Convert between binary and hexadecimal Split the 8 bits into two nibbles; each nibble is one hex digit from 0 to F. Binary, denary and hexadecimal
Add two 8-bit binary numbers Work from right to left, writing each carry clearly under the next column. Binary addition, overflow and shifts
Carry out a left or right shift Move every bit the given number of places and fill the empty places with 0s. Binary addition, overflow and shifts
Use a given code to find others Codes run in sequence, so if 'A' is 65 then 'D' is 68. Characters: ASCII and Unicode
Explain why Unicode was introduced ASCII has too few codes for other alphabets and symbols; Unicode uses more bits so it can represent far more characters. Characters: ASCII and Unicode
Explain what metadata is and why it's needed Data about the image, such as width, height and colour depth, so the computer can display it correctly. Images
Work out colours from colour depth n bits per pixel give 2ⁿ colours, e.g. 3 bits give 8 colours. Images
Explain how sample rate affects quality More samples per second, so the digital recording is closer to the original sound. Sound
Explain how bit depth affects quality More bits per sample give more possible values, so each sample is recorded more accurately. Sound
Give suitable uses of each type Lossy: photos, music and video; lossless: text, program code and spreadsheets. Compression
Define bandwidth and latency Bandwidth is the amount of data that can be transferred per second; latency is the delay before data arrives. LANs, WANs and network performance
Give advantages and disadvantages of each model E.g. client–server has central backups and security but costs more and the server is a single point of failure. Client–server and peer-to-peer
Describe how a switch uses MAC addresses A switch reads the destination MAC address and sends the data only to the device it is for. Network hardware
Describe how a router uses IP addresses A router reads the destination IP address and forwards packets between networks towards their destination. Network hardware
Describe the steps of a DNS lookup The browser sends the domain name to a DNS server, which finds the IP address (asking other servers if needed) and returns it. The Internet, DNS, hosting and the cloud
Describe the roles of web servers and clients The browser requests a page; the web server sends the page's files back; the browser displays it. The Internet, DNS, hosting and the cloud
Give advantages and disadvantages of each topology E.g. a star is easy to add to but fails if the switch fails; a mesh is reliable but expensive. Star and mesh topologies
Describe what Bluetooth is used for Short-range, low-power wireless links between nearby devices, e.g. headphones, keyboards and smartwatches. Ethernet, Wi-Fi and Bluetooth
Explain how encryption protects intercepted data Intercepted data is meaningless without the key; only the intended receiver can decrypt it. Encryption
Encrypt and decrypt with a Caesar cipher Shift each letter a fixed number of places along the alphabet, wrapping round from Z to A. Encryption
Describe IPv4 and IPv6 formats IPv4 is 32 bits written as four numbers from 0 to 255; IPv6 is 128 bits written as eight groups of four hex digits. IP and MAC addressing
Explain why IPv6 was introduced IPv4 gives only about 4.3 billion addresses, which is not enough for all connected devices. IP and MAC addressing
Choose the right protocol for a task E.g. FTP to upload website files, HTTPS to enter card details, IMAP to keep email in sync across devices. Standards and common protocols
State benefits of using layers Layers are self-contained, so they can be changed or developed separately. The concept of layers
Describe the main types of malware Virus, worm, trojan, ransomware and spyware, and how each one spreads or causes harm. Threats to computer systems and networks
Explain how phishing and social engineering work They trick people into giving away information or access, by exploiting trust, fear or urgency. Threats to computer systems and networks
Describe how a firewall works It monitors incoming and outgoing traffic and blocks data that does not meet its rules. Identifying and preventing vulnerabilities
Describe how anti-malware software works It scans files, compares them with a database of known malware, and quarantines or deletes threats. Identifying and preventing vulnerabilities
Describe memory management and multitasking Loads programs into RAM, gives each its own area, frees memory, and shares the processor between programs. Operating systems
Explain the role of a device driver Software that translates the OS's instructions into commands a particular device understands. Operating systems
Describe how defragmentation improves performance It moves the parts of each file together, so the read/write head moves less and files load faster. Utility software
Explain why compression software is used Smaller files take up less storage and transfer faster, e.g. to fit an email attachment limit. Utility software
Describe environmental impacts of technology E-waste, energy used by devices and data centres, and mining for raw materials, plus benefits such as less travel. Ethical, cultural, environmental and privacy issues
Explain privacy issues of data collection Location tracking, data sold to advertisers and data breaches can expose personal information. Ethical, cultural, environmental and privacy issues
Identify the law broken in a situation E.g. reading a colleague's emails using their password breaks the Computer Misuse Act 1990. Legislation
Describe the principles of the Data Protection Act Personal data must be used fairly and lawfully, for stated purposes, kept accurate, secure and no longer than needed. Legislation
Describe advantages and disadvantages of each E.g. open source is usually free and customisable but may lack official support. Open source and proprietary software
Apply abstraction to a scenario Say which details a program or model keeps and which it ignores, using the scenario's own objects. Computational thinking
Complete a partly drawn structure diagram Add the missing boxes at the correct level, under the correct parent box. Inputs, processes, outputs and structure diagrams
Complete missing parts of an algorithm Fill gaps in pseudocode or a flowchart so that it meets the description. Pseudocode and flowcharts
Complete a trace table for a loop Record each new value of every variable, and the output, in the correct order. Trace tables and common errors
Carry out a binary search on a list Find the middle item, compare, discard half the list, and repeat until found or empty. Linear and binary search
Describe the steps of a bubble sort Compare pairs, swap, finish the pass, then repeat passes until a pass makes no swaps. Bubble sort
Merge two sorted lists into one Compare the front item of each list and move the smaller one across, repeatedly. Merge sort
Show the list after each insertion Insert the second item, then the third, and so on, writing the list after each one. Insertion sort
Describe the steps of an insertion sort Start with the second item, shift larger sorted items right, and insert the item in the gap. Insertion sort
Trace a sequence of assignments Work out each variable's value line by line, remembering the right side is worked out first. Variables, constants, input, output and assignment
Compare count- and condition-controlled loops A for loop repeats a set number of times; while and do … until repeat depending on a condition. Sequence, selection and iteration
Work out the output of a loop Follow for loops with step values and while loops, including the last time round. Sequence, selection and iteration
Evaluate expressions using MOD, DIV and ^ 17 MOD 5 = 2, 17 DIV 5 = 3 and 2 ^ 3 = 8. Arithmetic, comparison and Boolean operators
Combine conditions with AND, OR, NOT Work out whether a combined condition is True or False. Arithmetic, comparison and Boolean operators
Explain what casting is Converting a value from one data type to another, such as the string "12" to the integer 12. Data types and casting
Use length, upper and lower word.length gives the number of characters; .upper and .lower change the case. String manipulation
Extract part of a string Use .substring(start, n), .left(n) and .right(n), counting positions from 0. String manipulation
Open, read and close a file Use open(), readLine() and close() in the correct order. File handling
Create a file and write to it Use newFile(), open() and writeLine(), then close the file. File handling
Declare and assign values in an array Use array scores[5] to declare it, then scores[0] = 12 to assign a value. Arrays and records
Explain what a record is A group of related fields about one item, which can be of different data types. Arrays and records
State the output of a simple query Pick out the fields named after SELECT for every record that meets the WHERE condition. SQL
Write a query using SELECT, FROM and WHERE Choose the fields, the table and a condition such as Minutes < 120. SQL
Tell functions and procedures apart A function returns a value; a procedure does not. Functions and procedures
Give benefits of using sub programs Code is reused, easier to test and maintain, and can be shared between programmers. Functions and procedures
Give uses of random numbers Games, simulations, choosing random items and generating test data. Random number generation
Describe ways to make code maintainable Sub programs, meaningful names (naming conventions), indentation and comments. Defensive design
Explain what authentication is Checking that users are who they say they are, for example with a username and password. Defensive design
Complete a test plan with expected results Give test data, its type and whether it should be accepted or rejected. Testing
Compare iterative and final testing Iterative happens during development; final testing is of the whole program at the end. Testing
Complete a truth table for two gates Add a column for the first gate, then work out the final output. Logic gates, diagrams and truth tables
Give features of high-level languages English-like, easier to write and debug, and portable between processor types. Languages and translators
Give features of low-level languages Processor-specific, direct control of hardware, fast and memory-efficient. Languages and translators
Describe features of the editor Syntax highlighting, auto-indentation, auto-completion, line numbers. The Integrated Development Environment
Complete a test plan for a scenario Choose normal, boundary, invalid and erroneous data with expected results. Paper 2 Section B practice: design, write, test and refine
Complete or correct lines of given code Fill gaps or fix errors so the code does what the scenario needs. Paper 2 Section B practice: design, write, test and refine

Grade 6

Grade 6 checklist (PDF)

Describe the fetch stage in order The address in the PC is copied to the MAR, the instruction at that address is copied from RAM into the MDR, and the PC is incremented. Architecture of the CPU
Explain why more cores don't always help Some programs can only use one core, some tasks cannot be split up, and cores take time to coordinate. CPU performance
Compare embedded and general-purpose computers A laptop runs many programs that the user can change; an embedded system runs one fixed program. Embedded systems
Describe how virtual memory works When RAM is full, data that is not currently needed is moved to an area of secondary storage, and moved back when needed. Primary storage (RAM, ROM, cache, virtual memory)
Recommend storage for a given scenario Choose a device and justify it with characteristics that are linked to how it will be used. Secondary storage
Calculate the size of a text file Bits per character × number of characters, then divide by 8 for bytes. Units and capacity
Convert between denary and hexadecimal Hex to denary: first digit × 16 + second digit; denary to hex: divide by 16 and use the remainder. Binary, denary and hexadecimal
Explain why hexadecimal is used It is shorter and easier for people to read and write than binary, so fewer mistakes are made, and it converts easily. Binary, denary and hexadecimal
Explain what an overflow error is The result of a calculation is too large to be stored in the number of bits available, e.g. more than 255 in 8 bits. Binary addition, overflow and shifts
State the effect of a shift Each place of left shift multiplies by 2; each place of right shift divides by 2. Binary addition, overflow and shifts
Link bits per character to characters represented n bits give 2ⁿ characters, so each extra bit doubles the number of characters. Characters: ASCII and Unicode
Explain effects of resolution and colour depth Increasing either improves the quality of the image but increases the file size. Images
Explain what affects the file size Increasing the sample rate, the bit depth or the duration increases the file size. Sound
Choose a compression type for a file Pick lossy where a small loss of quality is acceptable and lossless where the file must stay exactly the same. Compression
Explain why a busy network slows down Link the cause to the effect, e.g. more users share the bandwidth, so each gets less and transfers take longer. LANs, WANs and network performance
Explain why a model suits a scenario Link features such as cost, central backups or security to the needs of the organisation described. Client–server and peer-to-peer
Compare copper, fibre and wireless media Fibre has the highest bandwidth and range and no electrical interference but costs more; wireless gives mobility but is slower. Network hardware
Give advantages and disadvantages of the cloud Access from anywhere and no hardware to maintain, but it needs an Internet connection and a third party holds the data. The Internet, DNS, hosting and the cloud
Explain how a mesh network re-routes data There are several routes between devices, so if one link fails the data is sent a different way. Star and mesh topologies
Compare Ethernet and Wi-Fi in detail Make each point a comparison: bandwidth, reliability, interference, security, mobility and installation cost. Ethernet, Wi-Fi and Bluetooth
Give examples of where encryption is used HTTPS web pages, Wi-Fi networks and the storage on laptops and phones. Encryption
Explain how routers and switches use addresses Routers use IP addresses to route data between networks; switches use MAC addresses to deliver data within a LAN. IP and MAC addressing
Compare POP with IMAP Both retrieve email; POP downloads it and usually deletes it from the server, IMAP keeps it on the server and in sync. Standards and common protocols
Explain two benefits of layers in detail E.g. a change to one layer does not affect the others, so new hardware works without changing applications. The concept of layers
Explain why people are the weak point People can be tricked, choose weak passwords or be careless, and technical defences cannot stop this. Threats to computer systems and networks
Explain the purpose of penetration testing Authorised, simulated attacks find weaknesses so they can be fixed before criminals exploit them. Identifying and preventing vulnerabilities
Compare a GUI with a command-line interface A GUI is easier for beginners; a command line uses fewer resources and is faster for experts. Operating systems
Describe how encryption software protects files Files are scrambled using a key, so a thief cannot read them without the key or password. Utility software
Consider the views of different stakeholders E.g. how one change affects customers, staff, the company and society in different ways. Ethical, cultural, environmental and privacy issues
Describe the three Computer Misuse Act offences Unauthorised access; unauthorised access with intent to commit further offences; unauthorised acts to impair a computer. Legislation
Describe what licences allow and forbid Proprietary licences usually forbid copying, sharing and modifying; open source licences allow these under conditions. Open source and proprietary software
Decompose a given problem into sub-problems Split a system, such as a booking app or a game, into sensible named tasks. Computational thinking
Draw a structure diagram for a scenario Put the whole system at the top and break it down over two or more levels. Inputs, processes, outputs and structure diagrams
Write an algorithm with selection and iteration Write pseudocode or draw a flowchart that uses decisions and loops correctly. Pseudocode and flowcharts
Find and correct a logic error Use the expected output to find the line that gives the wrong result, then rewrite it. Trace tables and common errors
Compare linear and binary search Binary search is much quicker on large sorted lists; linear search works on unsorted lists. Linear and binary search
Explain how the sort knows it has finished A pass with no swaps means every pair is in order, so the list is sorted. Bubble sort
Show every stage of a merge sort Show all the splits down to single items, then each round of merging. Merge sort
Recognise insertion sort code Spot an outer loop from the second item and an inner loop that shifts items right. Insertion sort
Write code that inputs, processes and outputs Take input, cast it to the right type, calculate a result and output it. Variables, constants, input, output and assignment
Write code using if, elseif and else Choose the right order of conditions so that each case gives the correct result. Sequence, selection and iteration
Write a condition for a range For 13 to 19 inclusive: age >= 13 AND age <= 19. Arithmetic, comparison and Boolean operators
Explain why casting is needed in code Input is a string, so it must be cast before arithmetic, or + will join the strings. Data types and casting
Justify storing phone numbers as strings They can start with 0 or contain spaces, and no arithmetic is done on them. Data types and casting
Use ASC and CHR ASC("A") gives the character code 65; CHR(66) gives "B". String manipulation
Read every line until end of file Use a while loop with NOT file.endOfFile(). File handling
Loop through a 1D array Use for i = 0 to length − 1 to total, count or search the items. Arrays and records
Use * to select all fields SELECT * returns every field of each matching record. SQL
Identify parameters and return values Parameters receive values passed in; return sends a value back to where it was called. Functions and procedures
Write code that uses random numbers Store a random number in a variable and use it in selection or a loop. Random number generation
Write validation code with a loop Keep asking for the input until it meets the rule, giving a message if it is invalid. Defensive design
Explain why boundary data is tested Errors often happen at the limits, for example < used instead of <=. Testing
Write the expression for a logic diagram Work from the inputs to the output, using brackets to show which gate comes first. Logic gates, diagrams and truth tables
Draw a logic diagram from an expression Draw the gates in brackets first, then join their outputs to the final gate. Logic gates, diagrams and truth tables
Compare compilers and interpreters A compiler translates the whole program into an executable; an interpreter translates and runs line by line. Languages and translators
Explain how error diagnostics help They highlight errors and give messages with line numbers, so bugs are found quickly. The Integrated Development Environment
Write a program with input, selection and iteration Combine loops, if statements and variables to meet every requirement. Paper 2 Section B practice: design, write, test and refine

Grade 7

Grade 7 checklist (PDF)

Explain each component's role during the cycle Link each register and component to exactly what it stores, manages or controls at the fetch, decode and execute stages. Architecture of the CPU
Choose a CPU for a task and justify Use the figures in a table and link each characteristic to the task, e.g. multitasking benefits from more cores. CPU performance
Describe how an embedded system controls a device Describe the inputs (e.g. sensors), the decision it makes and the output it controls in an unfamiliar device. Embedded systems
Explain why virtual memory slows a computer Secondary storage is much slower than RAM, and data must be moved back into RAM before the CPU can use it. Primary storage (RAM, ROM, cache, virtual memory)
Evaluate storage options using given data Use capacities, speeds and costs from a table, including checking by calculation whether the data will fit. Secondary storage
Solve multi-step capacity problems E.g. find how many files fit in the space left on a device, rounding down to a whole number of files. Units and capacity
Reason about ranges and bit patterns E.g. n bits give 2ⁿ values, odd numbers end in 1, and why each hex digit matches exactly four bits. Binary, denary and hexadecimal
Explain the effect of bits being lost 1s shifted off the right make the result round down; 1s shifted off the left make the result wrong (overflow). Binary addition, overflow and shifts
Compare ASCII and Unicode, including file size Unicode covers many more characters but uses more bits per character, so text files are larger. Characters: ASCII and Unicode
Calculate an image's file size Colour depth × width × height gives the size in bits; divide by 8 for bytes. Images
Calculate the file size of a recording Sample rate × bit depth × duration in seconds gives bits; divide by 8 for bytes. Sound
Explain advantages and disadvantages of each type Lossy gives much smaller files but loses quality; lossless keeps every bit but saves less space. Compression
Use data to identify the limiting factor Decide from measurements whether bandwidth, latency or errors are causing poor performance, and justify a matching improvement. LANs, WANs and network performance
Recommend and justify a network model Weigh cost, number of computers, security and backups for the organisation, then give a justified recommendation. Client–server and peer-to-peer
Choose and justify hardware for a scenario Identify each item needed, e.g. for a café with Wi-Fi and a wired till, and explain why each one is needed. Network hardware
Calculate the connections in a full mesh A full mesh of n devices needs n(n − 1) ÷ 2 connections; a star needs n cables. Star and mesh topologies
Recommend a topology for a scenario Weigh reliability against cost for the organisation, and justify your choice. Star and mesh topologies
Recommend connections for a scenario Choose Ethernet, Wi-Fi or Bluetooth for each device and justify the choice using the scenario. Ethernet, Wi-Fi and Bluetooth
Explain why longer keys are more secure Each extra bit doubles the number of possible keys, so a brute-force attack takes far longer. Encryption
Explain why an IPv4 number cannot exceed 255 Each part is 8 bits, which gives 2⁸ = 256 values, from 0 to 255. IP and MAC addressing
Describe the roles of TCP and IP TCP splits data into numbered packets, checks and reassembles them; IP addresses and routes the packets. Standards and common protocols
Apply layers to an unfamiliar scenario E.g. explain why a browser still works when a laptop switches from Ethernet to Wi-Fi. The concept of layers
Explain the concept of SQL injection SQL code typed into an input box is run by the database, e.g. to bypass a login or reveal data. Threats to computer systems and networks
Match prevention methods to specific threats E.g. training for phishing, input validation for SQL injection, encryption for interception. Identifying and preventing vulnerabilities
Explain several OS functions in a scenario E.g. explain how the OS lets a user stream music, write an essay and print at the same time. Operating systems
Explain why SSDs should not be defragmented They have no moving parts, so there is no speed gain, and the extra writes shorten the SSD's life. Utility software
Explain how a law affects an organisation Apply the principles of the Data Protection Act to how a school or business handles personal data. Legislation
Recommend a type of software for a scenario Weigh cost, support, customisation and compatibility for the user, and justify the choice. Open source and proprietary software
Explain the benefits of decomposition Smaller parts are easier to code and test, can be shared between programmers and can be reused. Computational thinking
Explain how structure diagrams help development Each module can be coded and tested separately, shared between programmers and reused. Inputs, processes, outputs and structure diagrams
Convert between a flowchart and code Turn a flowchart into code, or code into a flowchart, keeping the same logic. Pseudocode and flowcharts
State the purpose of an algorithm Trace it with sample data and describe what it does overall, such as 'finds the largest value'. Trace tables and common errors
Complete or identify search algorithm code Recognise each search from its code and fill in missing lines, such as first = mid + 1. Linear and binary search
Complete bubble sort code, including the swap Use a temporary variable to swap two items, and a flag to record whether a swap happened. Bubble sort
Give advantages and disadvantages of merge sort Much faster on large lists, but uses more memory and is harder to code. Merge sort
Explain when insertion sort is a good choice It is quick for small lists and lists that are nearly sorted, and uses little memory. Insertion sort
Choose and write the most suitable loop Use for when the number of repeats is known and do … until when it must run at least once. Sequence, selection and iteration
Use MOD and DIV to solve problems Test for even numbers, or split a total into units, such as minutes and seconds. Arithmetic, comparison and Boolean operators
Work out the result and type of casts For example str(15) + "0" gives the string "150". Data types and casting
Loop through each character of a string Use for i = 0 to word.length - 1 with word.substring(i, 1). String manipulation
Process data read from a file Cast each line to the right type, then total, count or search it. File handling
Use a 2D array Access an element with two indexes, such as grid[2, 3]. Arrays and records
Combine conditions with AND and OR For example WHERE Genre = 'Sci-fi' AND Minutes > 130. SQL
Write a function with parameters Use function … endfunction, with parameters and a return statement. Functions and procedures
Explain local and global variables A local variable exists only in its sub program; a global variable can be used anywhere. Functions and procedures
Pick a random element from an array For an array of n items use the index random(0, n − 1). Random number generation
Explain how to anticipate misuse Plan for unexpected input, repeated login attempts and people trying to break the program. Defensive design
Use test results to find and fix errors Compare expected and actual results to locate a logic error and correct the line. Testing
Complete a three-input truth table List all 8 input combinations in order and work out each output. Logic gates, diagrams and truth tables
Choose a translator for a scenario Interpreter for development and debugging; compiler for distributing a finished program. Languages and translators
Describe using debugging tools to find errors Use breakpoints, stepping and watching variables to find a logic error. The Integrated Development Environment
Validate input inside a loop Keep asking until the input meets the rule, before using it. Paper 2 Section B practice: design, write, test and refine

Grade 8

Grade 8 checklist (PDF)

Trace register contents through an instruction Given an instruction, an address and the value stored there, state what the PC, MAR, MDR and accumulator hold at each step. Architecture of the CPU
Weigh up characteristics that point different ways Decide, for example, whether a faster clock or more cores matters more, depending on whether the software can use several cores. CPU performance
Recommend and justify a memory upgrade Explain why more RAM reduces the use of virtual memory, and why other upgrades may not help as much. Primary storage (RAM, ROM, cache, virtual memory)
Justify why alternatives are less suitable Explain why the other options would not work as well, not just why your choice does. Secondary storage
Work with 1000 and 1024 conventions Know that 1 KB can be taken as 1000 or 1024 bytes and use whichever the question states. Units and capacity
Solve problems combining shifts and addition E.g. multiply by 10 by adding the results of a left shift of 3 places (× 8) and a left shift of 1 place (× 2), and spot when overflow will happen. Binary addition, overflow and shifts
Calculate the bits needed for a character set Find the smallest n for which 2ⁿ is at least the number of characters needed. Characters: ASCII and Unicode
Compare file sizes after changes Use ratios, e.g. halving the width and height leaves a quarter of the pixels and a quarter of the file size. Images
Compare recordings using ratios E.g. 4 times the sample rate and 2 times the bit depth gives a file 8 times as large. Sound
Evaluate compression choices in a scenario Weigh storage, download time, bandwidth and the quality the user needs. Compression
Explain why more bandwidth may not fix lag When small amounts of data are sent many times a second, the delay (latency) matters more than the bandwidth. LANs, WANs and network performance
Evaluate moving an organisation to the cloud Weigh the benefits against the risks for the organisation described and reach a supported conclusion. The Internet, DNS, hosting and the cloud
Explain what encryption cannot protect against It does not stop data being intercepted or deleted, and does not help if the attacker has the key. Encryption
Describe an email's journey naming protocols SMTP to send and to pass between mail servers, POP or IMAP to retrieve, TCP/IP throughout. Standards and common protocols
Explain how data passes through the layers At the sender each layer adds its header on the way down; at the receiver each layer removes its header on the way up. The concept of layers
Discuss threats and their impact on organisations Explain how several attacks could happen to the organisation described and what their effects would be. Threats to computer systems and networks
Evaluate the security for an organisation Recommend and prioritise a combination of methods suited to the organisation's data, budget and staff. Identifying and preventing vulnerabilities
Write a balanced 8-mark discussion Cover each type of issue asked for, apply it to the scenario, give both sides and reach a conclusion. Ethical, cultural, environmental and privacy issues
Discuss legal issues in an unfamiliar scenario Link each action to the relevant law and consider the responsibilities of everyone involved. Legislation
Evaluate open source for an organisation Discuss cost, support, compatibility, training and security in an extended answer with a conclusion. Open source and proprietary software
Refine an algorithm to meet new requirements Change an existing algorithm, such as adding validation or a counter, without breaking it. Pseudocode and flowcharts
Trace nested loops and selection accurately Keep track of inner and outer loop counters and which branch runs each time. Trace tables and common errors
Work out the maximum number of comparisons Binary search halves the list each time, so 1000 items need at most 10 comparisons. Linear and binary search
Evaluate bubble sort against other sorts Simple and memory-efficient, but slow for large lists compared with merge sort. Bubble sort
Choose a suitable sort for a scenario Justify merge sort for large data sets, or another sort when memory or simplicity matters. Merge sort
Compare insertion, bubble and merge sort Weigh up speed on large lists, memory use and how sorted the data already is. Insertion sort
Use nested selection and iteration Put loops and if statements inside each other, with correct indentation and logic. Sequence, selection and iteration
Write functions that process strings For example count vowels, check a password's characters or build a code. String manipulation
Process a 2D array with nested loops Use an outer loop for one index and an inner loop for the other. Arrays and records
Write a simulation or game using random Combine random numbers with loops, counters and selection correctly. Random number generation
Explain the limits of validation Validation checks data is sensible, not that it is correct. Defensive design
Turn a written problem into logic Write an expression and truth table for a scenario, such as an alarm system. Logic gates, diagrams and truth tables
Use arrays, files or sub programs in solutions Store and process data with the right structure, such as an array of names. Paper 2 Section B practice: design, write, test and refine

Grade 9

Grade 9 checklist (PDF)

Refine a program to meet new requirements Change working code accurately, without breaking what it already does. Paper 2 Section B practice: design, write, test and refine

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