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Exam Board: OCR 1.1b Performance Specification: A-Level 2015 The performance of a computer system is affected by four main factors: Cache Memory: Size & Levels What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory, like RAM . What are the 3 levels of cache memory? Level 1 cache is the smallest level (less than a megabyte ) but it is also the fastest . Level 2 cache is larger than level 1 (up to 8 megabytes ) but slightly slower. Level 3 cache is located outside of the CPU core which makes it slower than the first two levels but it is much larger (up to 50 megabytes ). How does cache memory work? ​ When the CPU searches for data , it looks first in level 1 cache, then level 2, and then level 3 . If the data has been found , this is called a 'cache hit '. If the data is not found, the CPU searches in RAM instead, which takes more time - this is called a 'cache miss '. How does cache memory improve performance? Cache memory is closer to the CPU than RAM , meaning that it can provide data and instructions to the CPU at a faster rate . ​ A computer with more cache memory (e.g. 8MB instead of 4MB) should perform better because repeatedly used instructions can be stored and accessed faster . ​ Larger level 1 and level 2 cache sizes will improve a computer's performance as data can be accessed extremely quickly . What is the limitation of cache memory? Cache memory is costly, so most computers only have a small amount . ​ Multiple cache misses will result in data latency (delay) as information is accessed from RAM which is further away from the CPU. Clock Speed What is clock speed? Clock speed is the measure of how quickly a CPU can process instructions . ​ Clock speed is measured in Gigahertz (GHz) . A typical desktop computer might have a clock speed of 3.5 GHz . This means it can perform 3.5 billion cycles a second . How does clock speed improve performance? ​ The faster the clock speed, the faster the computer can perform the FDE cycle resulting in better performance because more instructions can be processed each second . How does overclocking and underclocking affect performance? Typical clock speed: 3.5 GHz Underclocking Overclocking 3.9 GHz 3.1 GHz Overclocking is when the computer's clock speed is increased higher than the recommended rate. ​ This will make the computer perform faster, but it can lead to overheating and could damage the machine . Underclocking is when the computer's clock speed is decreased lower than the recommended rate. ​ This will make the computer perform slower but will increase the lifespan of the machine . Number of Cores What is a core? ​ A core is a complete set of CPU components (control unit, ALU and registers). Each core is able to perform its own FDE cycle . ​ A multi-core CPU has more than one set of components within the same CPU. This page is still being updated. How does the number of cores improve performance? ​ In theory, a single-core processor can execute one instruction at a time , a dual-core processor can execute two instructions, and a quad-core can execute four instructions simultaneously . ​ Therefore, a computer with more cores will have a higher performance because it can process more instructions at once . What are the limitations of having more cores? ​ If one core is waiting for another core to finish processing, performance may not increase at all. ​ Some software is not written to make use of multiple cores , so it will not run any quicker on a multi-core computer. Pipelining What is pipelining? ​ Pipelining efficiently uses multiple cores or processors to perform different stages of the FDE cycle at the same time . Pipelining overlaps the processing of instructions to improve performance by increasing the amount of instructions that can be fetched, decoded and executed each second . ​ The first image to the right shows a processor not using pipelining whereby one instruction can only be fetched once the previous instruction has been fetched, decoded and executed. The second image shows how pipelining can be used to process multiple instructions during the same clock cycle . For example, in clock cycle 3 instruction X can be executed while instruction Y is decoded and instruction Z fetched. A simplified example of a processor not using pipelining. A simplified example of a processor using pipelining. What is the limitation of pipelining? ​ Certain instructions may not be able to be executed until other instructions have been fetched and decoded . This wait for other instructions may impact performance . Q uesto's Q uestions 1.1b - Performance: ​ Cache Size & Levels 1a. What is cache memory ? [ 2 ] 1b. Describe the three levels of cache memory , including the storage size and relative speed of each level. [ 6 ] 1c. Describe what is meant by a ' cache hit ' and a ' cache miss '. [ 2 ] 1d. Describe two ways that more c ache memory will mean performance is higher . [ 4 ] 1e. Explain why most computers only have a small amount of cache memory. [ 1 ] Clock Speed 2a. What is clock speed ? What is it measured in? [ 2 ] 2b. Explain how a higher clock speed improves performance . [ 2 ] 2c. Explain the terms 'overclocking ' and 'underclocking ' and explain the effects of both on the performance of a computer. [ 4 ] ​ Number of Cores 3a. What is a core ? [ 2 ] 3b. Explain why a quad-core processor should have a higher performance than a dual-core processor . [ 3 ] 3c. Explain two reasons why having more cores doesn't necessarily mean the performance will be better . [ 2 ] ​ Pipelining 4a. What is pipelining ? How does pipelining affect performance ? [ 4 ] 1.1a - The CPU & FDE Cycle Theory Topics 1.2 - Processors

OCR Computer Science A-Level Component 1: Computer Systems These pages are based on content from the OCR Computer Science 2015 specification . This website is in no way affiliated with OCR . 1. Hardware 1.1a - The CPU & FDE Cycle 1.1b - Performance 1.2 - Processors 1.3a - Input & Output Devices 1.3b - Memory & Storage 2. Software 2.1 - Operating Systems 2.2a - Applications & Utilities 2.2b - Translators & Compilation 2.3 - Software Development Methodologies 2.4a - Programming & Pseudocode 2.4b - Assembly Language 2.4c - Object-Oriented Language 3. Networks & Databases 3.1a - Compression 3.1b - Encryption & Hashing 3.2a - Databases & Normalisation 3.2b - SQL 3.3a - Network Characteristics 3.3b- Protocols & TCP-IP Stack 3.3c - Network Hardware & DNS 3.3d - Network Security & Threats 3.4a - Web Technologies 3.4b - HTML, CSS & JavaScript 4. Data & Logic 4.1a - Data Types & Character Sets 4.1b - Denary, Binary & Hexadecimal 4.1c - Signed Binary & Floating Point 4.1d - Binary Calculations 4.1e - Shifts & Masks 4.2 - Data Structures 4.3a - Logical Operators & Truth Tables 4.3b - Flip Flops, Adders, Laws & Maps 5. Laws 5.1 - Computer Legislation 5.2 - Moral & Ethical Issues

Exam Board: OCR 1.2 Processors Specification: A-Level 2015 An instruction set is a list of all the instructions that a CPU can process as part of the FDE cycle . ​ CPUs can have different sets of instructions that they can perform based on their function. The two most common instruction sets are the simpler RISC (Reduced Instruction Set Computer ) and more complicated CISC (Complex Instruction Set Computer ). Instruction Sets This page is still being updated. Reduced Instruction Set Computer (RISC) Complex Instruction Set Computer (CISC) Complexity RISC has fewer instructions than CISC and is therefore slower for carrying out complex commands but quick for basic tasks . CISC has more complex instructions available and can therefore perform complicated tasks . Cost RISC is generally cheaper to mass produce because less circuitry is required for the smaller instruction set. CISC CPUs are generally more expensive because they require more circuitry to operate. Power RISC CPUs are designed to use less power and run without dedicated cooling systems (like fans) so that they can be used in devices like smartphones . Because CISC CPUs require more circuitry this means that they generate more heat and may require a fan . CISC CPUs therefore are commonly used in desktop computers . Clock Speed RISC CPUs run at lower clock speeds than CISC CPUs. They can perform simpler tasks more quickly than CISC, but are generally not used to carry out complex instructions . CISC CPUs run at higher clock speeds than RISC CPUs. They can perform complex tasks more quickly than RISC. Graphical Processing Unit What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Q uesto's Q uestions 1.2 - Processors: ​ 1. What is cache memory ? [ 2 ] ​ 1.1b Performance Theory Topics 1.3a - Input & Output Devices

Exam Board: OCR 1.1a: The CPU & The FDE Cycle Specification: A-Level 2015 The Central Processing Unit ( CPU ) is the most important component in any computer system. ​ The purpose of the CPU is to process data and instructions by constantly repeating the fetch - decode - execute cycle . CPU Components The control unit directs the flow of data and information into the CPU. It also controls the other parts of the CPU . ALU stands for ‘ Arithmetic and Logic Unit ’. It performs simple calculations and logical operations . The registers are temporary storage spaces for data and instructions inside the CPU . ​ The registers are used during the FDE cycle . ​ Five essential registers are explained below. Important Registers A register is a small storage space for temporary data in the CPU . Each register has a specific role . There are five essential registers used in the FDE cycle : ​ Program Counter (PC) A register that tracks the RAM address of the next instruction to be fetched . Memory Address Register (MAR) A register that tracks the RAM address of data that is currently being accessed . Memory Data Register (MDR) ​ The MDR stores the data that is transferred from RAM to the CPU . Current Instruction Register (CIR) A register that stores the instruction that has been fetched from RAM , and is about to be decoded or executed . Accumulator (ACC) ​ The ACC stores the result of executions performed in the FDE cycle . The FDE Cycle The essential idea of the FDE cycle is that instructions are fetched from RAM , to be decoded (understood) and executed (processed) by the CPU . ​ The Fetch - Decode - Execute (FDE) cycle is performed by the CPU millions of times every second. ​ This cycle is how the CPU processes data and instructions for each program or service that requires its attention. 1. 2. 3. The Program Counter (PC ) register displays the address in RAM of the next instruction to be processed . This value is copied into the Memory Address Register (MAR ). 0054 The PC register is increased by 1 . ​ This prepares the CPU for the next instruction to be fetched. 0055 The CPU checks the address in RAM which matches the address held in the MAR . 0054 4. The instruction in RAM is transferred to the Memory Data Register (MDR ). MDR 5. The instruction in the MDR is copied into the Current Instruction Register (CIR ). MDR CIR 6. The instruction in the CIR is decoded (understood) and executed (processed). Any result of an execution is stored in the Accumulator (ACC ) register. CIR ACC 7. The cycle repeats by returning to the first step and checking the program counter for the address of the next instruction . Buses Data is transferred within a computer system along pathways called buses . ​ There are three types of bus: Address Bus Sends a memory address of where data is stored.​​ The address is sent from the CPU to RAM in the FDE cycle. Data Bus Transfers data between components. Data is sent both ways . Control Bus Sends control signals from the control unit to other components of the system. Status signals are sent back to the CPU. Think about which buses would be used during the FDE cycle and when. ​ For example, look back at stages 3 and 4 of the FDE cycle above. The address bus is used to send the address in RAM of the next instruction . The control bus is used to send the fetch signal . The data bus is used to transfer the instruction from RAM to the MDR . Computer Architecture The way a computer is designed and internally organised is known as its architecture . ​ The most common type of computer architecture is Von Neumann architecture . Von Neumann Architecture The key features of Von Neumann architecture include: The CPU , which constantly performs the FDE cycle , and contains: One control unit One ALU Special registers ​ D ata and instructions are stored in the same format in the same area in memory . Instructions are commands and data are the specific values used when processing. ​ Data and instructions are transferred across buses (pathways) between the CPU, memory and input or output devices. Harvard Architecture The key features of Harvard architecture include: ​ The CPU , which constantly performs the FDE cycle , and contains: One control unit One ALU ​ D ata and instructions are stored in separate areas in memory . Instructions are commands and data are the specific values used when processing. ​ Data and instructions are transferred across buses (pathways) between the CPU, data memory, instruction memory and input or output devices. Q uesto's Q uestions 1.1a - The Central Processing Unit (CPU): ​ 1a. What does 'CPU ' stand for ? [1 ] 1b. What is the purpose of the CPU ? [ 2 ] ​ 2a. Draw a diagram of the CPU , use the same symbols as shown on this page. [ 4 ] 2b. Label the three main components of the CPU. [ 4 ] ​ 3. Describe the purpose of: a. The Control Unit [ 2 ] b. The ALU [ 2 ] c. The registers [ 2 ] ​ 4a. Describe the key features of Von Neumann architecture . [ 3 ] 4b. Describe the differences between the two main types of architecture. [ 2 ] This page is still being updated. Theory Topics 1.1b - Performance

Exam Board: OCR 3.2a - Databases & Normalisation Specification: A-Level 2015 An instruction set is a list of all the instructions that a CPU can process as part of the FDE cycle . ​ CPUs can have different sets of instructions that they can perform based on their function. The two most common instruction sets are the simpler RISC (Reduced Instruction Set Computer ) and more complicated CISC (Complex Instruction Set Computer ). Instruction Sets This page is still being updated. Graphical Processing Unit What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Q uesto's Q uestions 3.2a - Databases & Normalisation: ​ 1. What is cache memory ? [ 2 ] ​ 3.1b - Encryption & Hashing Theory Topics 3.2b - SQL

8.1: Programming Principles Exam Board: Eduqas / WJEC Specification: 2020 + Problem Solving There are four stages to computational thinking (smart problem solving ). Decomposition is when you break a problem down into smaller tasks so that it is easier to solve . Pattern Recognition is the process of identifying similar patterns within a problem . Abstraction is when you ignore unnecessary information and focus only on the important facts . Algorithms are the final stage as step-by-step rules are created to solve the problem . An algorithm is usually written as psuedocode or presented as a flowchart . Programming Constructs There are three constructs (ideas) of programming that most programs will contain: Sequence Structuring code into a logical, sequential order . Selection Decision making using if statements . Iteration Repeating code , often using for loops or while loops . Variables Large programs are often modular - split into subroutines with each subroutine having a dedicated purpose. Local variables are declared within a specific subroutine and can only be used within that subroutine . ​ Global variables can be used at any point within the whole program . ​ Local variable advantages Saves memory - only uses memory when that local variable is needed - global variables use memory whether they are used or not. Easier to debug local variables as they can only be changed within one subroutine. You can reuse subroutines with local variables in other programs. ​ Global variable advantages Variables can be used anywhere in the whole program (and in multiple subroutines). Makes maintenance easier as they are only declared once. Can be used for constants - values that remain the same. Local & Global Variables Constants A variable is data that can change in value as a program is being run. ​ A constant is data that does not change in value as the program is run - it is fixed and remains the same. ​ An example of a constant in maths programs is pi - it will constantly remain at 3.14159 and never change. π π Counts & Rogue Values When using iteration (looping) the loop must eventually be able to stop. A count is a variable that is used to record the current iteration (loop number). ​ A rogue value is an unexpected value that will cause the loop to end . For example by typing "Stop" into a loop that asks for numbers. Self-documenting Identifiers An efficient program will use variables with sensible names that immediately state their purpose in the program. ​ Using variable names like 'TotalNum' and 'Profit' rather than 'num1' and 'num2' mean that other programmers will be able to work out the purpose of the code without the need for extensive comments. Q uesto's Q uestions 8.1 - Programming Principles: ​ Problem Solving 1. What is meant by 'decomposition '? Why is it important ? [2 ] 2. What does the term 'abstraction ' mean? Why is it important ? [2 ] 3. What is pattern recognition ? [2 ] 4a. What is an algorithm ? [1 ] 4b. What are the two ways of writing an algorithm ? [2 ] ​ Programming Constructs 1. Describe and draw a diagram for the 3 programming constructs . [6 ] ​ Variables 1. What is the difference between local and global variables ? [4 ] 2. Describe two advantages of using local variables . [2 ] 3. Describe two advantages of using global variables . [2 ] 4. What is a constant ? Give an example . [2 ] 5. Why is it important to use self-documenting identifiers when programming? [2 ] 6. What is a count ? What is a rogue value ? [2 ] ​ 7.1 - Language Levels Theory Topics 8.2 - Understanding Algorithms

3.1 - Server Types Exam Board: OCR Specification: 2016 - Unit 1 What is a server? A server is a powerful dedicated system on a network. It requires increased memory, storage and processing power than traditional computer systems to fulfill its role across the network. Servers need to be scalable - this means they must be adaptable and able to efficiently manage the needs of connected systems . Servers have different roles so a company may use multiple server types within their organisation, each with a specific purpose. File Server A file server centrally stores and manages files so that other systems on the network can access them. ​ The server provides access security , ensuring that only users of the appropriate access level can access files. File servers can be used to automatically backup files , as per the organisation's disaster recovery policy. Using a file server frees up physical storage space within a business and can provide printing services too. Printer Server These servers control any printers on a network and manage printing requests by sending the document to an appropriate printer. ​ Print servers use spooling to queue print jobs so that they are printed when the printer is ready. If a fault occurs with a certain printer, work can be automatically diverted to another available printer. Application Server These servers allow users to access shared applications on a network. All users will be able to access common applications like email software or word processing but the server will also restrict certain applications to those with invalid access levels (such as hiding financial databases from employees outside of the finance department). Simplified updates can be deployed just to the application server instead of each machine that runs the application, saving a lot of time. ​ Installers can be found on an application server, allowing the software to be easily installed on other machines. Database Server These servers manage database software that users on the network can access and use to manipulate data . Data held on the server will be stored in a database accessible from multiple connected computers . The data can be modified using query languages such as SQL. ​ Storing data on a database server, rather than individual computers, is more reliable . A database server for a business also allows for scaling - for example, the database can be increased in size if the customer base grows. Web Server A web server manages HTTP requests from connected devices to display web pages on web browsers . A request (e.g. csnewbs.com) is sent to the web server. The server contains a list of known URLs and their matching IP addresses . The server contacts the server where the web page is held and delivers the web page to the client . Mail Server These servers send and receive emails using email protocols (SMTP & POP) allowing email communication between other mail servers on other networks. ​ The server makes sure emails are delivered to the correct user on the network. ​ Email servers can store company address books making internal communication easier for organisations. ​ The server may have anti-spam functions to reduce junk mail. Hypervisor A hypervisor allows a host machine to operate virtual machines as guest systems. The virtual machines share the resources of the host , including its memory, processing power and storage space. ​ This type of technology is called virtualisation . The guest machines are isolated so if one failed, the other guests and the hosts are not affected - demonstrating good security . ​ The hypervisor optimises the hardware of the host server to allow the virtual machines to run as efficiently as possible. Q uesto's Q uestions 3.1 - Server Types: 1a. What is a server ? Why does it need to be scalable ? [2 ] 1b. State the 7 types of server . [1 each ] ​ 2. A medium-sized animation company working on a movie are considering buying a server. Describe each type of server and the different roles they have. a. File Server b. Printer Server c. Application Server d. Database Server e. Web Server f. Mail Server g. Hypervisor [4 each ] 3. What type of technology does a hypervisor use to control multiple virtual machines? [1 ] 2.7 - Protocols Topic List 3.2 - Virtualisation

3.1: Defensive Design Exam Board: OCR Specification: J277 Defensive Design Considerations There are several things to consider when creating a program that is secure and robust , including: Anticipating Misuse Planning ahead to take steps against potential misuse (e.g the app X prevents the same tweet sent twice in a row as it might be spam ). Input Sanitisation Checking and cleaning up data that has been input , (e.g. removing special characters to prevent a SQL injection ). Validation Checking whether input data follows specific criteria and should be accepted (e.g. a length check on a password). Verification Checking whether data that has been entered is correct (e.g. double entry ). Authentication Ensuring only authorised users can gain access to a system (e.g. usernames and strong passwords ) . ​ Maintainable code Allowing other programmers to easily read and quickly understand code that has been written (e.g. using comments , indentation and appropriate variable names ). Input Validation Validation is a process to check that data is reasonable or sensible before it is accepted . Range Check Checks data is within a certain range . Age: 34 203 Type Check Checks data is a certain data type . Height (in cm): 182 Two metres Format Check Checks data is entered in a certain way . Date of Birth (DD/MM/YYYY) 25/03/2011 25th March 11 Presence Check Checks that data has actually been entered and not left blank . Password: fluffythecat123 Lookup Table A table of acceptable entries , also known as a list . Length Check Checks the length of the input is within a certain amount. Telephone Number 08323877319 07383 Maintainability Programs should be written in a way that makes maintaining and understanding them as straightforward as possible. Examples of making a program maintainable include: Using subprograms to reuse code and make them easier to test . This is called modularisation . Appropriate variable names , using a naming convention , ensure the purpose of a variable is immediately understood. Using indentation to improve readability and clearly show each ‘block’ of code. Comments enable a programmer to understand the purpose of each line of code. Crucial when working in a team . Using constants is another method of improving maintainability. This keeps the program code consistent , which makes it easier to read and debug a program. Q uesto's Q uestions 3.1 - Defensive Design: ​ 1. Describe the different considerations a programmer should make for a defensive design . [ 6 ] ​ 2. Describe the each validation check and give a suitable example . [ 12 ] ​ 3. Explain the different ways a program can be maintained . [ 5 ] 2.3 Additional Programming Theory Topics 3.2 - Testing

Exam Board: OCR 3.1f - Searching Algorithms Specification: A-Level 2015 An instruction set is a list of all the instructions that a CPU can process as part of the FDE cycle . ​ CPUs can have different sets of instructions that they can perform based on their function. The two most common instruction sets are the simpler RISC (Reduced Instruction Set Computer ) and more complicated CISC (Complex Instruction Set Computer ). Instruction Sets This page is still being updated. Graphical Processing Unit What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Q uesto's Q uestions 3.1f - Searching Algorithms: ​ 1. What is cache memory ? [ 2 ] ​ 3.1e - Sorting Algorithms Theory Topics 3.1g - Pathfinding

4.1: Security Threats Exam Board: OCR Specification: J277 Types of Malware ​Malware is any type of harmful program that seeks to damage or gain unauthorised access to your computer system. Virus A virus can replicate itself and spread from system to system by attaching itself to infected files . A virus is only activated when opened by a human . Once activated, a virus can change data or corrupt a system so that it stops working . Worm A worm can replicate itself and spread from system to system by finding weaknesses in software . A worm does not need an infected file or human interaction to spread. A worm can spread very quickly across a network once it has infiltrated it. Trojan A trojan is a harmful program that looks like legitimate software so users are tricked into installing it . A trojan secretly gives the attacker backdoor access to the system . Trojans do not self replicate or infect other files. Spyware Spyware secretly records the activities of a user on a computer. The main aim of spyware is to record usernames, passwords and credit card information . All recorded information is secretly passed back to the attacker to use. Keylogger A keylogger secretly records the key presses of a user on a computer. Data is stored or sent back to the attacker. The main aim of a keylogger is to record usernames, passwords and credit card information . Keyloggers can be downloaded or plugged into the USB port . Ransomware Ransomware locks files on a computer system using encryption so that a user can no longer access them. The attacker demands money from the victim to decrypt (unlock) the data . ? ? ? ? Attackers usually use digital currencies like bitcoin which makes it hard to trace them. SQL Injection SQL ( Structured Query Language ) is a programming language used for manipulating data in databases . ​ A SQL injection is when a malicious SQL query (command) is entered into a data input box on a website. ​ If the website is insecure then the SQL query can trick the website into giving unauthorised access to the website’s database . ​ An SQL injection can be used to view and edit the contents of a database or even gain administrator privileges . DoS Attack A DoS (Denial of Service ) attack is when a computer repeatedly sends requests to a server to overload the system . A server overload will slow the system and may take websites offline temporarily. ​ A DDoS (Distributed Denial of Service ) attack is a coordinated attack using a botnet of infected systems to overload a server with requests . A botnet is a large group of devices controlled and used maliciously by an attacker. Brute-Force Attack Every possible combination is tested in order from start to finish . This is not a quick method but it should break the password eventually and can be sped up if multiple computer systems are used at the same time. Social Engineering Social engineering means to trick others into revealing their personal data by posing as a trusted source . For example, impersonating an IT technician of a school via email and asking for a student's username and password . Data Interception This is when data packets on a network are intercepted by a third party (e.g. a hacker) and copied to a different location than the intended destination. ​ Software called packet sniffers are used to intercept and analyse data packets. 4.1 - Security Threats: 1. What is malware ? [ 2 ] 2a. Describe three characteristics of a virus . [3 ] 2b. Describe three characteristics of a worm . [3 ] 2c. What is a trojan ? [ 3 ] 2d. Describe how spyware and keyloggers work. [ 4 ] 2e. Explain how ransomware works and why it is difficult to trace attackers . [ 3 ] 2f. In your opinion, which malware do you think is the most dangerous and why ? [ 2 ] 3. Describe what an SQL injection is and how an attacker would use it. [ 3 ] ​ 4a. Describe what a DoS attack is and its impact . [2 ] 4b. Describe how a DDoS attack is different to a DoS attack . [2 ] ​ 5a. Describe a brute-force attack. [ 2 ] 5b. Describe social engineering and give an example of when it might be used . [2 ] 5c. Describe interception . [2 ] Q uesto's Q uestions 3.2b - Protocols & Layers Theory Topics 4.2 - Preventing Vulnerabilities

Scams & Staying Safe Part 1: Phishing Scams A phishing scam is when an attacker will send you an email pretending to be someone you trust . They are trying to get your username, password or other sensitive information . What does a phishing email look like? Capital letters and exclamation marks may be used to create a sense of urgency. A phishing email might be sent from a long, unrecognisable email address . It may be similar but slightly different to a real email address. An attacker might not know your name , so they will use your email address. A phishing email might contain spelling and grammar mistakes , so look carefully. Check any links carefully , if it looks suspicious, don't click it. Phishing emails try to rush you into making a silly decision. Don't panic and read the email carefully. Part 2: Secure webpages When you are browsing the web , you should stick to websites that you know and trust. Don't click on any links that you don't recognise , especially from strangers . How do i know a web page is secure? HTTP is a protocol (set of rules) for displaying a web page . ​ If the web address at the top of your web browser starts with HTTP then it is not secure . ​ Do not enter any personal information on an insecure web page. HTTPS is a protocol (set of rules) for displaying a secure web page. If you see a padlock in the address bar of your web browser then you know it is safer to enter information . Part 3: Strong passwords Your passwords must be secure so they cannot be broken easily. How to choose a strong password: ********* Passwords should be more than at least 8 characters long. Passwords should use numbers and punctuation marks . Aa Bb Cc Dd Ee Passwords should use uppercase and lowercase letters . You should use a different password for each account that you have. Passwords should not use words found in the dictionary . KS3 Home

Exam Board: OCR 2.2b: Translators & Compilation Specification: A-Level 2015 An instruction set is a list of all the instructions that a CPU can process as part of the FDE cycle . ​ CPUs can have different sets of instructions that they can perform based on their function. The two most common instruction sets are the simpler RISC (Reduced Instruction Set Computer ) and more complicated CISC (Complex Instruction Set Computer ). Instruction Sets This page is still being updated. Graphical Processing Unit What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Multicore & Parallel Systems What is cache memory? ​ Cache memory is temporary storage for frequently accessed data . ​ Cache memory is very quick to access because it is closer to the CPU than other types of memory like RAM . Q uesto's Q uestions 2.2b - Translators & Compilation: ​ 1. What is cache memory ? [ 2 ] ​ 2.2a - Applications & Utilities Theory Topics 2.3 - Software Development