AQA Level 1/Level 2 GCSE (9-1) in Computer Science

addition

Be familiar with and be able to use:

eg the calculation 11/2 would generate the following values:

Integer division, including remainders, is usually a two stage process and uses modular arithmetic:

integer division, including remainders.

Integer division: the integer quotient of 11 divided by 2 (11 DIV 2) = 5

multiplication

real division

Remainder: the remainder when 11 is divided by 2 (11 MOD 2) = 1

subtraction

Answers will be a maximum of 8 bits in length and will not involve carrying beyond the 8th bit.

Be able to add together up to three binary numbers.

Be able to apply a binary shift to a binary number.

Binary shifts can be used to perform simple multiplication/division by powers of 2.

Describe situations where binary shifts can be used.

Students will be expected to understand and use only a logical binary shift.

Students will be expected to use a maximum of 8 bits.

Students will need to be able to add together up to three binary numbers using a maximum of 8 bits per number.

Students will not need to understand or use fractional representations.

Students will only be expected to add together a maximum of three 1s in a single column.

. to represent the AND gate + to represent the OR gate ⊕ to represent the XOR gate Overbar to represent the NOT gate

A . B + C

AND

Construct truth tables for simple logic circuits using combinations of NOT, AND, OR and XOR gates.

Construct truth tables for the following logic gates:

Create a logic circuit from a simple Boolean expression.

Create and interpret simple Boolean expressions made up of NOT, AND, OR and XOR operations.

Create the Boolean expression for a simple logic circuit.

Create, modify and interpret simple logic circuit diagrams.

For example the expression (A AND B) OR (NOT C) would be represented as:

Interpret the results of simple truth tables.

NOT

OR

Students do not need to know about or use NAND and NOR logic gates.

Students should be able to construct simple logic circuit diagrams which contain up to three inputs.

Students should be able to construct truth tables which contain up to three inputs.

Students will be expected to understand and use the following Boolean expression operators:

Students will be expected to understand and use the following logic circuit symbols:

Students will only need to use NOT, AND, OR and XOR gates within logic circuits.

XOR.

AND

Be familiar with and be able to use:

NOT

OR.

Students should be able to use these operators, and combinations of these operators, within conditions for iterative and selection structures.

7-bit ASCII

convert character codes to characters.

convert characters to character codes

Describe the purpose of Unicode and the advantages of Unicode over ASCII.

It is not necessary to be familiar with UTF-8, UTF-16 or other different versions of Unicode.

Know that Unicode uses the same codes as ASCII up to 127.

Students should be able to explain the need for data representation of different alphabets and of special symbols allowing a far greater range of characters.

Students should be able to use a given character encoding table to:

Students should know that character codes are grouped and that they run in sequence. For example in ASCII ‘A’ is coded as 65, ‘B’ as 66, and so on, meaning that the codes for the other capital letters can be calculated once the code for ‘A’ is known. This pattern also applies to other groupings such as lower case letters and digits.

Understand that character codes are commonly grouped and run in sequence within encoding tables.

Understand what a character set is and be able to describe the following character encoding methods:

Unicode.

assembler.

assemblers and compilers translate their input into machine code directly

compiler

each line of assembly language is assembled into a single machine code instruction

Explain the main differences between low-level and high-level languages.

Explain the main differences between these three types of translator.

high-level language.

interpreter

interpreters do not generate machine code directly (they call appropriate machine code subroutines within their own code to carry out statements).

Know that machine code and assembly language are considered to be low-level languages and explain the differences between them.

Know that there are different levels of programming language:

low-level language

Students should understand that most computer programs are written in high-level languages and be able to explain why this is the case.

Students will need to know that:

Understand that all programming code written in high-level or assembly languages must be translated.

understand that assembly language has a 1:1 correspondence with machine code.

understand that assembly language is often used to develop software for embedded systems and for controlling specific hardware components

Understand that machine code is expressed in binary and is specific to a processor or family of processors.

understand that processors execute machine code and that each type of processor has its own specific machine code instruction set

Understand that there are three common types of program translator:

Understand the advantages and disadvantages of low-level language programming compared with high-level language programming.

Understand when it would be appropriate to use each type of translator.

Boolean logic

Classification of programming languages and translators

Hardware and software

Software classification

Systems architecture

Be able to convert in both directions between:

binary and decimal

binary and hexadecimal

binary: 1111 1111

decimal and hexadecimal.

decimal: 255

hexadecimal: FF

Students must be able to represent decimal values between 0 and 255 in binary.

Students must be able to represent decimal values between 0 and 255 in hexadecimal.

The following equivalent maximum values will be used:

Understand how binary can be used to represent whole numbers.

Understand how hexadecimal can be used to represent whole numbers.

Cyber security threats

Fundamentals of cyber security

Malicious code (malware)

Methods to detect and prevent cyber security threats

Social engineering

Explain what penetration testing is and what it is used for.

malicious code (malware)

misconfigured access rights

Penetration testing is the process of attempting to gain access to resources without knowledge of usernames, passwords and other normal means of access.

pharming

Pharming is a cyber attack intended to redirect a website's traffic to a fake website.

removable media

social engineering techniques

Students should understand the following two types of penetration testing:

Understand and be able to explain the following cyber security threats:

unpatched and/or outdated software.

weak and default passwords

when the person or team testing the system has knowledge of and possibly basic credentials for the target system, simulating an attack from inside the system (a malicious insider)

when the person or team testing the system has no knowledge of any credentials for the target system, simulating an attack from outside the system (an external attack).

Be able to calculate the number of bits required to store a piece of data compressed using Huffman coding.

Be able to calculate the number of bits required to store a piece of uncompressed data in ASCII.

Be able to interpret Huffman trees.

eg 0000011100000011

Explain how data can be compressed using Huffman coding.

Explain how data can be compressed using run length encoding (RLE).

Explain what data compression is.

Represent data in RLE frequency/data pairs. Students could be given a bitmap representation and they would be expected to show the frequency and value pairs for each row,

Students should be familiar with carrying out calculations to determine the number of bits saved by compressing a piece of data using Huffman coding.

Students should be familiar with the process of using a tree to represent the Huffman code.

Students should be familiar with the process of using frequency/data pairs to reduce the amount of data stored.

Students should understand that it is common for data to be compressed and should be able to explain why it may be necessary or desirable to compress data.

Understand why data may be compressed and that there are different ways to compress data.

An example of a record definition would be:

Only one and two-dimensional arrays are required.

RECORD Car make : String model : String reg : String price : Real noOfDoors : Integer ENDRECORD

Understand the concept of data structures. It may be helpful to set the concept of a data structure in various contexts that students may already be familiar with. It may also be helpful to suggest/demonstrate how data structures could be used in a practical setting.

Use arrays (or equivalent) in the design of solutions to simple problems.

Use records (or equivalent) in the design of solutions to simple problems.

Boolean

character

Depending on the actual programming language(s) being used, these data types may have other names. For example real numbers may be described as float. In exams we will use the general names given opposite.

integer

real

string.

Understand and use the following appropriately:

Understand the concept of a data type.

Compare the efficiency of algorithms explaining how some algorithms are more efficient than others in solving the same problem.

Exam questions in this area will only refer to time efficiency.

Formal comparisons of algorithmic efficiency are not required.

Understand that more than one algorithm can be used to solve the same problem.

autonomous vehicles.

cloud storage

computer based implants

cyber security

Ethical, legal and environmental impacts of digital technology

Exam questions will be taken from the following areas:

Explain the current ethical, legal and environmental impacts and risks of digital technology on society. Where data privacy issues arise these should be considered.

hacking (unauthorised access to a computer system)

mobile technologies

Students should be aware that governments and security services often argue that they cannot keep their citizens safe from terrorism and other attacks unless they have access to private data.

Students should be aware that ordinary citizens normally value their privacy and may not like it when governments or security services have too much access.

Students will be expected to understand and explain the general principles behind the issues rather than have detailed knowledge on specific issues.

wearable technologies

wireless networking

Efficiency of algorithms

Representing algorithms

Searching algorithms

Sorting algorithms

application layer

Application layer: this is where the network applications, such as web browsers or email programs, operate.

authentication

bus.

Define the term network protocol.

Define what a computer network is.

Describe the 4 layer TCP/IP model:

Describe the following common LAN topologies:

Describe the main types of computer network including:

Discuss the advantages and disadvantages of computer networks.

Discuss the advantages and disadvantages of wireless networks as opposed to wired networks.

email protocols:

encryption

Ethernet

Explain the following methods of network security:

Explain the purpose and use of common network protocols including:

firewall

FTP (File Transfer Protocol)

Fundamentals of computer networks content

HTTP (Hypertext Transfer Protocol)

HTTPS (Hypertext Transfer Protocol Secure)

IMAP (Internet Message Access Protocol).

internet layer

Internet layer: addresses and packages data for transmission. Routes the packets across the network.

IP (Internet Protocol)

LAN – know that these are often owned and controlled/managed by a single person or organisation.

LAN – know that these usually cover relatively small geographical areas.

Link layer: this is where the network hardware such as the NIC (network interface card) is located. OS device drivers also sit here.

link layer.

Local Area Network (LAN)

MAC address filtering.

PAN – only Bluetooth needs to be considered.

Personal Area Network (PAN)

SMTP (Simple Mail Transfer Protocol)

star

Students should be able to draw topology diagrams and describe the differences between the two topologies. They should also be able to select the most appropriate topology for a given scenario.

Students should be able to explain, using examples, what each of these security methods is and when each could be used.

Students should be able to name the layers and describe their main function(s) in a networking environment.

Students should know that wired networks can use different types of cable such as fibre and copper and when each would be appropriate.

Students should know what each protocol is used for (eg HTTPS provides an encrypted version of HTTP for more secure web transactions).

Students should understand how these methods can work together to provide a greater level of security.

Students should understand that Ethernet is a family of related protocols rather than a single protocol. They do not need to know the individual protocols that make up the Ethernet family.

Students should understand that MAC address filtering allows devices to access, or be blocked from accessing a network based on their physical address embedded within the device’s network adapter.

Students should understand that Wi-Fi is a family of related protocols rather than a single protocol. They do not need to know the individual protocols that make up the Wi-Fi family but they should know that Wi-Fi is a trademark and that the generic term for networks of this nature is WLAN.

TCP (Transmission Control Protocol)

Teachers should be aware that the link layer is sometimes referred to as the network access layer or network interface layer. However, students will not be expected to know these alternative layer names.

The capabilities of firewalls have changed dramatically in recent years and will continue to do so. Students should be aware that a firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules.

transport layer

Transport layer: this layer sets up the communication between the two hosts and they agree settings such as the size of packets.

UDP (User Datagram Protocol)

Understand that networks can be wired or wireless.

Understand that the HTTP, HTTPS, SMTP, IMAP and FTP protocols operate at the application layer.

Understand that the IP protocol operates at the internet layer.

Understand that the TCP and UDP protocols operate at the transport layer.

Understand the need for, and importance of, network security.

WAN – know that the Internet is the biggest example of a WAN.

WAN – know that these are often under collective or distributed ownership.

WAN – know that these usually cover a wide geographic area.

Wi-Fi

Wide Area Network (WAN).

Be able to define the term cyber security and be able to describe the main purposes of cyber security.

Students should know that cyber security consists of the processes, practices and technologies designed to protect networks, computers, programs and data from attack, damage or unauthorised access.

Binary Arithmetic

Character Codes

Character Encoding

Converting between number bases

Data compression

Number bases

Quantities of Bytes

Representing images

Representing sound

Units of information

Define the terms hardware and software and understand the relationship between them.

Be able to obtain user input from the keyboard.

Be able to output data and information from a program to the computer display.

computer virus

Define the term malware.

Describe the following forms of malware:

Describe what malware is and how it can be protected against.

Malware is an umbrella term used to refer to a variety of forms of hostile or intrusive software.

spyware.

trojan

automatic software updates.

biometric measures (particularly for mobile devices)

CAPTCHA (or similar)

password systems

Understand and be able to explain the following security measures:

using email confirmations to confirm a user’s identity

binary (base 2)

decimal (base 10)

Explain why hexadecimal is often used in computer science.

hexadecimal (base 16).

Students should be familiar with the idea that a bit pattern could represent different types of data including text, image, sound and integer.

Understand that computers use binary to represent all data and instructions.

Understand the following number bases:

Arithmetic operations in a programming language

Boolean operations in a programming language

Data structures

Data types

Exam questions will explicitly state in what form the response needs to be provided. This will be, for example, pseudo-code, program code or a flowchart, and students must respond as instructed. Where pseudo-code is an accepted method of response, students may present their answers to questions in any suitable format and do not need to use the AQA pseudo-code.

Input/output

Programming concepts

Random number generation in a programming language

Relational operations in a programming language

Robust and secure programming

String handling operations in a programming language

Structured programming and subroutines (procedures and functions)

Students need a practical understanding of all the topics and skills in this section for the paper 1 exam. When they are writing computer programs in an exam they will need to ensure they use meaningful identifier names, use suitable data types and that all logic flow is clearly identifiable to examiners.

Students need a theoretical understanding of all the topics in this section for the paper 1 exam even if the programming language(s) taught does not support all of the topics. Exams will always present algorithms using the current version of the AQA pseudo-code. The document can be found on the AQA website.

Use of arrays and records

A theoretical understanding of condition(s) at either end of an iterative structure is required, regardless of whether they are supported by the language(s) being used.

An example of definite (count controlled) iteration would be:

An example of indefinite (condition controlled) iteration with the condition at the start would be:

An example of nested iteration would be:

An example of nested selection would be:

assignment

constant declaration

DO … Instructions here … WHILE NotSolved

Examples of indefinite (condition controlled) iteration with the condition at the end would be:

FOR i ← 1 TO 5 … Instructions here … ENDFOR

Identifier names include names for variables, constants and subroutine names.

IF GameWon THEN … Instructions here … IF Score > HighScore THEN … Instructions here … ENDIF … Instructions here … ENDIF

iteration

REPEAT … Instructions here … UNTIL Solved

selection

Students should be able to write programs using these statement types. They should be able to interpret and write algorithms that include these statement types.

Students should know why named constants and variables are used.

subroutine (procedure/function).

The three combining principles (sequence, iteration/repetition and selection/choice) are basic to all high-level imperative programming languages.

Use definite (count controlled) and indefinite (condition controlled) iteration, including indefinite iteration with the condition(s) at the start or the end of the iterative structure.

Use meaningful identifier names and know why it is important to use them.

Use nested selection and nested iteration structures.

Use, understand and know how the following statement types can be combined in programs:

variable declaration

WHILE NotSolved … Instructions here … ENDWHILE

WHILE NotSolved … Instructions here ... FOR i ← 1 TO 5 … Instructions here … ENDFOR … Instructions here … ENDWHILE

Be able to use random number generation. Students will be expected to use random number generation within their computer programs. An understanding of how pseudo- random numbers are generated is not required.

data type

Explain the concept of a database.

Explain the concept of a relational database.

field

foreign key.

Note that whilst the terms entity, attribute and entity identifier are more commonly used when an abstract model of a database is being considered, the terms given here will be used for both implementations of and abstract models of databases.

primary key

record

table

Understand that the use of a relational database facilitates the elimination of data inconsistency and data redundancy.

Understand the following database concepts:

Database Concepts

Relational databases

Structured Query Language (SQL)

Students should be able to use these operators within their own programs and be able to interpret them when used within algorithms. Note that different languages may use different symbols to represent these operators.

Any exam question where students are given pseudo-code will use the AQA standard version.

Be aware that a computer program is an implementation of an algorithm and that an algorithm is not a computer program.

Decomposition means breaking a problem into a number of sub-problems, so that each sub- problem accomplishes an identifiable task, which might itself be further subdivided.

Determine the purpose of simple algorithms. Students should be able to use trace tables and visual inspection to determine how simple algorithms work and what their purpose is.

Exam questions will indicate the form of response expected. For example, pseudo-code, program code or a flowchart.

Explain simple algorithms in terms of their inputs, processing and outputs.

Students must be able to identify where inputs, processing and outputs are taking place within an algorithm.

Understand and explain the term abstraction. Abstraction is the process of removing unnecessary detail from a problem.

Understand and explain the term algorithm. An algorithm is a sequence of steps that can be followed to complete a task.

Understand and explain the term decomposition.

Use a systematic approach to problem solving and algorithm creation representing those algorithms using pseudo-code, program code and flowcharts.

Calculate bitmap image file sizes based on the number of pixels and colour depth.

Colour depth is the number of bits used to represent each pixel.

colour depth.

Convert a bitmap image into binary data. Given a simple bitmap, students should be able to write down a bit pattern that represents the image.

Convert binary data into a bitmap image. Given a binary pattern that represents a simple bitmap, students should be able to draw the resulting image as a series of pixels.

D = colour depth in bits.

Describe how a bitmap represents an image using pixels and colour depth.

Describe the following for bitmaps:

Describe using examples how the number of pixels and colour depth can affect the file size of a bitmap image.

H = image height

image size

Know that the size of a bitmap image is measured in pixels (width x height).

Size = (bits) = W x H x D

Size = (bytes) = (W x H x D)/8

Students only need to use colour depth and number of pixels within their calculations.

Students should be able to describe how higher numbers of pixels and higher colour depths can affect file size, and should also be able to use examples.

Students should be able to explain how bitmaps are made from pixels.

Students should know that the term pixel is short for picture element. A pixel is a single point in an image.

The size of an image is expressed directly as width of image in pixels by height of image in pixels using the notation width x height.

Understand what a pixel is and be able to describe how pixels relate to an image and the way images are displayed.

W = image width

Calculate sound file sizes based on the sampling rate and the sample resolution.

Describe the digital representation of sound in terms of:

File size (bits) = rate x res x secs

rate = sampling rate

res = sample resolution

Sample resolution is the number of bits per sample.

sample resolution.

sampling rate

Sampling rate is the number of samples taken in a second and is usually measured in hertz (1 hertz = 1 sample per second).

secs = number of seconds

Students should understand that a sample is a measure of amplitude at a point in time.

Understand that analogue signals are sampled to create the digital version of sound.

Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer.

Be able to correct errors within algorithms and programs.

Be able to identify and categorise errors within algorithms and programs.

Be able to select and justify the choice of suitable test data for a given problem.

Be able to write simple authentication routines. Students should be able to write a simple authentication routine that uses a username and password. Students will only be required to use plain text usernames and passwords (ie students will not need to encrypt the passwords).

Be able to write simple data validation routines. Students should be able to use data validation techniques to write simple routines that check the validity of data being entered by a user.

boundary (extreme)

Boundary data would be for example:

checking if a string is empty

checking if an entered string has a minimum length

checking if data entered lies within a given range (eg between 1 and 10).

erroneous data.

If the allowed range is 1 to 10, then boundary data is 0, 1, 10, 11, ie either side of the allowed boundary.

logic error.

normal (typical)

syntax error

The following validation checks are examples of simple data validation routines:

Understand that there are different types of error:

Understand what is meant by testing in the context of algorithms and programs.

Understand what test data is and describe the following types of test data:

Compare and contrast linear and binary search algorithms.

Students should know the advantages and disadvantages of both algorithms.

Students should know the mechanics of the algorithm.

Understand and explain how the binary search algorithm works.

Understand and explain how the linear search algorithm works.

blagging (pretexting)

Blagging is the act of creating and using an invented scenario to engage a targeted victim in a manner that increases the chance the victim will divulge information or perform actions that would be unlikely in ordinary circumstances.

Define the term social engineering.

Describe what social engineering is and how it can be protected against.

Explain the following forms of social engineering:

phishing

Phishing is a technique of fraudulently obtaining private information, often using email or SMS.

shouldering (or shoulder surfing).

Shouldering is observing a person's private information over their shoulder eg cashpoint machine PIN numbers.

Students should know that social engineering is the art of manipulating people so they give up confidential information.

application software is software that performs end-user tasks.

application software.

applications

Explain what is meant by:

Give examples of both types of software.

input/output (I/O) devices

memory

processor(s)

security.

Students should understand that:

system software

system software manages the computer system resources and acts as a platform to run application software

Understand that the OS handles management of the:

Understand the need for, and functions of, operating systems (OS) and utility programs.

Compare and contrast merge sort and bubble sort algorithms.

Students should know the advantages and disadvantages of both algorithms.

Students should know the mechanics of the algorithm.

Understand and explain how the bubble sort algorithm works.

Understand and explain how the merge sort algorithm works.

concatenation

convert character code to character

convert character to character code

Expected string conversion operations:

integer to string

length

position

real to string.

string conversion operations.

string to integer

string to real

substring

Understand and be able to use:

are only accessible within the subroutine.

Describe the structured approach to programming.

Describe the use of parameters to pass data within programs.

Explain the advantages of the structured approach.

Explain the advantages of using subroutines in programs.

Know that subroutines may declare their own variables, called local variables, and that local variables usually:

only exist while the subroutine is executing

Students should be able to describe how data is passed out of a subroutine using return values.

Students should be able to describe how data is passed to a subroutine using parameters.

Students should be able to describe the structured approach including modularised programming, clear well-documented interfaces (local variables, parameters) and return values.

Students should be able to use subroutines that require more than one parameter.

Teachers should be aware that the terms arguments and parameters are sometimes used but in examinable material we will use the term parameter to refer to both of these.

Understand the concept of subroutines. Students should know that a subroutine is a named ‘out of line’ block of code that may be executed (called) by simply writing its name in a program statement.

Use local variables and explain why it is good practice to do so.

Use subroutines that return values to the calling routine.

Be able to use SQL to edit and delete data in a database using the commands.

Be able to use SQL to insert data into a relational database using the commands.

Be able to use SQL to retrieve data from a relational database, using the commands:

DELETE FROM table_name WHERE condition

Exam questions will require that data is extracted from no more than two tables for any one query.

FROM

INSERT INTO table_name (column 1, column 2 …) VALUES (value 1, value 2 …)

ORDER BY…ASC | DESC

SELECT

UPDATE table_name SET column 1 = value 1, column 2 = value 2 ... WHERE condition

WHERE

A bus is a collection of wires through which data/signals are transmitted from one component to another.

arithmetic logic unit

Be aware of different types of secondary storage (solid state, optical and magnetic).

bus.

Cache

cache size.

clock

clock speed

control unit

decode: the instruction is decoded to work out what it is

Discuss the advantages and disadvantages of solid state, optical and magnetic storage.

execute: the instruction is executed (carried out). This may include reading/ writing from/to main memory.

Explain the advantages and disadvantages of cloud storage when compared to local storage.

Explain the effect of the following on the performance of the CPU:

Explain the operation of solid state, optical and magnetic storage.

Explain the role and operation of main memory and the following major components of a central processing unit (CPU) within the Von Neumann architecture:

Explain the term cloud storage. Students should understand that cloud storage uses magnetic and/or solid state storage at a remote location.

fetch: the next instruction is fetched to the CPU from main memory

Know what the different types of memory are used for and why they are required.

Knowledge of specific registers is not required.

Main memory will be considered to be any form of memory that is directly accessible by the CPU (except for cache and registers).

number of processor cores

RAM

register

Register.

ROM

Secondary storage is considered to be any non- volatile storage mechanism not directly accessible by the CPU.

Students must be able to give examples of embedded and non-embedded systems.

Students should be able to explain the terms volatile and non-volatile.

Students should be aware that SSDs use electrical circuits to persistently store data but will not need to know the precise details such as use of NAND gates.

The CPU continually reads instructions stored in main memory and executes them as required:

Understand and explain the Fetch-Execute cycle.

Understand the differences between main memory and secondary storage.

Understand the differences between RAM and ROM.

Understand the different types of memory within a computer:

Understand the term embedded system and explain how an embedded system differs from a non-embedded system.

Understand why secondary storage is required.

A bit is either a 0 or a 1.

a bit is the fundamental unit of information

a byte is a group of 8 bits.

b represents bit

B represents byte

Be able to compare quantities of bytes using the prefixes above.

giga, 1 GB is 1,000 Megabytes

kilo, 1 kB is 1,000 bytes

Know that quantities of bytes can be described using prefixes.

Know that:

Know the names, symbols and corresponding values for the decimal prefixes:

mega, 1 MB is 1,000 kilobytes

Students might benefit from knowing that historically the terms kilobyte, megabyte, etc have often been used to represent powers of 2.

tera, 1 TB is 1,000 Gigabytes.

The International System of Units (SI units) kilo, mega and so forth refer to values based on powers of 10. When referring to powers of 2 the terms kibi, mebi and so forth would normally be used but students do not need to know these.