OCR GCSE J277 Computer Science Comprehensive Glossary

Systems Architecture and the Central Processing Unit

Central Processing Unit (CPU): A chip within the computer which controls the operation of all parts of the computer and decodes then executes program instructions.
Fetch-Execute Cycle: A process where instructions are fetched one by one from main memory, decoded, and then executed by the processor. This cycle repeats until the program is complete.
Arithmetic Logic Unit (ALU): The part of the CPU responsible for arithmetic and logical operations.
Processor Cache: High-speed memory built into the CPU. Instructions are copied to cache memory, allowing them to be accessed more quickly and therefore increasing the speed of the CPU.
Register: A small area of memory within the CPU where data is stored temporarily to avoid the delay in copying to and from main memory.
Von Neumann Architecture: The design on which most computers are based. It defines several registers along with the fetch-execute cycle and how the CPU interacts with main memory.
Memory Address Register (MAR): A register that contains the address of the instruction currently being read from or written to main memory.
Memory Data Register (MDR): A register that contains the instruction which has just been copied from main memory.
Program Counter: A register that contains the address of the next instruction to be fetched from memory. It is updated each time a new instruction is fetched to contain the address of the next needed instruction.
Accumulator: A register that stores the result of the last operation.

CPU Performance and Embedded Systems

Clock Speed: How many instruction cycles the CPU can deal with in a second, measured in $MHz$ or $GHz$ . Faster speeds represent better performance.
Cache Size: The larger the amount of cache the CPU has, the more instructions it can store without having to transfer to main memory, leading to faster performance.
Cores: Some CPUs have more than one core. Each core contains its own ALU and registers, making it capable of carrying out instructions independently. More cores allow the CPU to process more instructions at once, increasing performance.
Embedded System: Specialist hardware and software built into a device with a single specific purpose. These are typically found within appliances such as washing machines.

Memory and Secondary Storage

Primary Storage (Memory): Holds the data, programs, and instructions currently in use.
Random Access Memory (RAM): Stores programs and data before they are processed by the CPU. It is read/write memory, meaning contents can be changed. RAM is volatile, so contents are lost when the computer is turned off.
Read Only Memory (ROM): Data can be retrieved but not changed. It is non-volatile, meaning contents are not lost when the computer is turned off. Often used to store programs for embedded systems.
Volatile Memory: Data stored in volatile memory is lost when the computer is turned off.
Non-Volatile Memory: Data stored in non-volatile memory is not lost when the computer is turned off.
Virtual Memory: Space on the computer's hard drive used as main memory (RAM). Virtual memory is slower than main memory.
Optical Storage: A type of secondary storage that stores data on a spinning plastic or metal disk. Data is read from and written to the disk using a laser.
Magnetic Storage: A type of secondary storage that uses magnetic fields to store data. A read/write head interacts with the media.
Solid State Storage: A type of secondary storage that uses flash memory to store data. These have no moving parts and are much faster than optical or magnetic storage.
Hard Disk Drive (HDD): A magnetic storage drive that can store large amounts of data. It is often the main method of secondary storage in personal computers and contains internal disks and a read/write head.
Digital Versatile Disk (DVD): A high-capacity optical storage disk commonly used for video storage, with capacities available up to $17\,GB$ .
Compact Disk (CD): An optical storage disk often used for music, with a capacity usually around $800\,MB$ .
Solid State Drive (SSD): A solid-state storage drive performing the function of a traditional HDD but with faster speeds and higher durability due to having no moving parts. They are generally more expensive and have lower capacities than HDDs.

Data Units and Storage Standards

Bit: The smallest unit of storage, containing a binary $1$ or $0$ .
Nibble: $4$ bits (half a byte).
Byte: $8$ bits.
Kilobyte (KB): $1000\,bytes$ .
Megabyte (MB): $1000\,KB$ .
Gigabyte (GB): $1000\,MB$ .
Terabyte (TB): $1000\,GB$ .
Petabyte (PB): $1000\,TB$ .
Binary: A number system used by computers containing only two symbols: $0$ and $1$ . It is also known as base 2.
Denary: The number system most often used by people, known as base 10 or decimal. It uses digits $0$ through $9$ .
Integer: A whole number without a decimal point or fraction, such as $1$ , $100$ , or $88122$ .
Overflow Error: Occurs when not enough space has been allocated to store the results of a calculation, such as a $9$ -bit result being placed in an allocated space of one byte.
Hexadecimal: A base 16 number system used in computing.
Binary Shift: A process used to perform mathematics on binary numbers by moving all digits to the left or right.
Most Significant Bit (MSB): The furthest left digit in a string of binary numbers; its position gives it the highest value.
Least Significant Bit (LSB): The furthest right digit in a string of binary numbers; its position gives it the lowest value.

Representing Images, Sound, and Text

Character: A single symbol, such as a letter, number, or punctuation mark.
Character Set: A system for representing characters in binary; each character is assigned a unique binary number.
ASCII: American Standard Code for Information Interchange. A $7$ -bit character set used to represent characters.
Unicode: A large character set created to overcome the limited characters available in ASCII. It includes different language characters and symbols like emojis.
Pixel: Short for Picture Element. Pictures are divided into a grid, where each square is one pixel of a single color.
Metadata: Additional data about a file, such as creation date or author. In photos, it stores camera make or location.
Colour Depth: The amount of bits available for colors in an image. Higher color depth allows for more realistic images.
Resolution: The number of pixels an image is divided into. Higher resolution results in clearer images.
Sample Rate: The number of samples taken in one second, measured in Hertz ( $Hz$ ). $1\,Hz$ is one sample per second. Higher rates result in higher file quality.
Bit Depth: The number of bits available for each sample. Higher bit depth increases file quality.

Compression Techniques

Compression: A method of reducing file size, often used with photos, music, and video files.
Lossy Compression: Reduces file size by removing certain data. The original file cannot be restored from the compressed version, but it offers greater size reduction than lossless methods.
Lossless Compression: Reduces file size without losing any data. The original file can be fully restored, though the size reduction is less significant than lossy compression.

Computer Networks and Topologies

Network: Two or more computers connected together for sharing data or resources.
Local Area Network (LAN): A network covering a small geographic area, such as a single building.
Wide Area Network (WAN): A network covering a large geographic area.
Client-Server: A network setup where resources or processing are handled by a central computer (server) and accessed by other devices (clients).
Peer to Peer: A setup where all computers have equal status and function as both client and server.
Wireless Access Point (WAP): Uses a wireless radio to allow devices to connect wirelessly to an existing network.
Router: A device connecting two or more different networks to allow communication between them.
Switch: A device providing computers and other hardware with a wired connection to a network.
Network Interface Card (NIC): A component within a device that provides the physical connection to a network.
Transmission Media: The physical connection—such as cables or wireless signals—that carries data between devices.
Domain Name System (DNS): A system linking a URL or human-readable name with an IP address.
Hosting: Storing files or data on a server (the host).
The Cloud: Accessing storage or resources remotely across the Internet.
Web Server: A server hosting websites and pages for user access via the Internet.
Network Topology: The way in which computers and devices are connected together.
Star Network: A topology where all devices connect back to a single central point. All communication travels via this center.
Mesh Network: A topology where all devices are connected to each other rather than a central point.
Bandwidth: The amount of data $(bits)$ that can be transferred via a network in a given time. Higher bandwidth results in faster transfer speeds.
The Internet: A global network connecting millions of devices.
URL (Uniform Resource Locator): A human-readable name for websites and Internet resources, translated by DNS into an IP address.
Client: A device that accesses data from a central server.

Network Protocols and Standards

Ethernet: Physical copper cabling used for network connections. The term also refers to the protocols and standards controlling data transmission on the cable.
Wi-Fi: Technology using wireless signals to connect network devices.
Bluetooth: A short-range wireless technology with low range and speed, typically used for peripherals like mice or headsets.
Encryption: Converting data into a format that cannot be easily read or understood without first being decrypted. Used for security during network transfers.
IP Address (Internet Protocol Address): A unique address assigned to every computer on a network.
IPv4: Internet Protocol Version 4. Addresses consist of four numbers separated by dots (e.g., $232.112.11.1$ ), with each number between $0$ and $255$ .
IPv6: Internet Protocol Version 6. Designed to address the limited addresses in IPv4, using eight groups of hexadecimal characters (e.g., $FE80:CD00:0000:0CDE:1257:0000:211E:729C$ ).
MAC Address (Media Access Control Address): A unique $12$ -digit hexadecimal number assigned to a network interface card at the time of manufacture.
Standard: An agreed way of doing something, allowing different organizations to create products and services that work together.
Protocol: An agreed set of rules for how network communications should take place.
TCP/IP (Transfer Control Protocol / Internet Protocol): A group of standards controlling how data is sent and received over networks/the Internet.
HTTP (Hypertext Transfer Protocol): A standard for transferring web pages based on a client request and server response.
HTTPS (Hypertext Transfer Protocol Secure): A secure version of HTTP, commonly used for online banking.
FTP (File Transfer Protocol): A standard for transferring files over networks.
POP (Post Office Protocol): A standard used by email clients to retrieve emails from a server.
IMAP (Internet Message Access Protocol): A standard used to access emails stored on a server, allowing them to be organized on the server (an advantage over POP).
SMTP (Simple Message Transfer Protocol): A standard used for sending emails over networks and the Internet.

Network Security Threats and Defenses

Malware: Software designed with malicious intent to damage computers, monitor activity, or delete data.
Social Engineering: Targeting people instead of technical measures to gain system access. Examples include watching someone enter a password or impersonating an authority figure.
Phishing: Tricking individuals into revealing private information, like passwords or financial data, by pretending to be a trusted entity via email.
Brute-force Attack: Attempting to guess a password by trying every single possible solution, often through dictionaries or lists of common passwords.
Denial of Service (DoS) Attack: Sending more traffic to a computer system than it can handle, causing system failure.
Data Interception: Accessing data while it is being transferred between devices. Attackers can steal credentials or files without the victim's knowledge.
SQL Injection: Entering malicious SQL code into input fields on a website to interact directly with a database to access, change, or delete data.
Penetration Testing: An authorized hacking attempt to find security flaws so they can be fixed before actual hackers exploit them.
Anti-Malware Software: Software like Anti-Virus designed to detect, prevent, and remove malicious software.
Firewall: A security device that checks network traffic against a set of rules, blocking unauthorized devices or protocols.
User Access Level: Controlling which parts of a system users can access to prevent accidental or deliberate damage to sensitive areas.
Password: A secret phrase used with a username to control system access.
Physical Security: Securing the physical hardware of a system, such as locking a computer to a desk or using reinforced server rooms.

Systems and Utility Software

Operating System (OS): Controls the operation of all computer aspects and provides a user interface.
User Interface: The part of the OS allowing interaction via graphical components, typing commands, or using touchscreens.
Memory Management: The OS function managing memory usage and application access.
Multitasking: The ability of an OS to run multiple tasks or applications simultaneously.
Peripheral Management: Controlling hardware devices like printers, mice, or speakers.
Device Driver: Code providing instructions for the OS on how to interact with specific hardware.
User Management: Manages accounts, passwords, and access rights for multiple users on the same computer.
File Management: Manages files and folders on internal or external storage.
Access Rights: Manages permissions that applications and users have within the system.
Encryption Software: Software that turns data into code readable only with the correct key.
Defragmentation Software: Reorders files on a hard disk to run in a sensible order, improving performance.
Data Compression Software: Compresses data to save storage space.

Ethical, Legal, Cultural, and Environmental Impacts

Ethical: Principles of right and wrong behavior, independent of legality.
Legal: Rules regarding behaviors and punishments. Laws vary by country and are updated over time.
Cultural: Normal expectations in daily life, such as common design choices (e.g., red delete buttons).
Environmental: Matters relating to the natural world, atmosphere, and animal well-being.
Privacy: The expectation that personal information, like medical history, is kept secret.
The Data Protection Act (2018): UK law governing the processing of personal data and defining the rights of data providers.
Computer Misuse Act (1990): UK law making misuse of computer systems illegal under specific criteria.
Copyright Designs and Patents Act (1998): UK law providing legal protection for works and materials.
Software License: An agreement between a software creator and user regarding rules of use; may require payment.
Open Source Software: Software with code available to the public to view, edit, and use for free.
Proprietary Software: Software where the source code is owned and kept private by an individual or organization.

Algorithms and Computational Thinking

Computational Thinking: Thinking using computational means to create solutions a computer can implement.
Abstraction: Removing unnecessary information to focus on the essential parts of a problem.
Decomposition: Breaking a large problem into smaller, manageable parts.
Algorithmic Thinking: Working out the individual steps needed for an algorithmic solution.
Algorithm: A sequence of logical instructions to carry out a specific task.
Structure Diagram: A graphical representation of the steps to solve a problem (e.g., a flowchart).
Pseudocode: A method of writing algorithms that falls between natural language and computer code.
Flowchart: Using shapes and pictures to represent the steps of a program.
Programming Language: A language understood by computers to produce software.
Error: An issue in code causing it either to fail to run or to produce incorrect output.
Trace Table: A table recording variable values at each stage of a program to find errors.

Searching and Sorting Algorithms

Search: Finding a specific value within a data set.
Binary Search: Searching an ordered list by checking the middle item and narrowing the search space to the halves above or below the target value.
Linear Search: Checking items in a list one at a time until the value is found.
Sort: Ordering information alphabetically or numerically.
Bubble Sort: Comparing items two at a time and swapping them until the list is ordered.
Merge Sort: Dividing a list into individual items and then merging them back together in pairs in the correct order.
Insertion Sort: Working through items one at a time and placing them in their correct position relative to others.

Programming Fundamentals and Data Types

Variable: A named, changeable value in which data is stored during program execution.
Constant: A named, fixed value that cannot be changed by the program.
Operator: Used to compare or modify values (e.g., $+$ , $<$ , and $NOT$ ).
Input: Data put into a program from a user or sensor.
Output: Information produced by a program for a screen, printer, or file.
Assignment: The process of putting a value into a variable.
Sequence: Following steps in a specific order.
Selection: Taking different paths through code based on conditions.
Iteration: Repeating a set of steps.
Count Controlled Loop: Running code a specific number of times using a counter.
Condition Controlled Loop: Repeating code until a specific condition is met.
Arithmetic Operator: Uses mathematics to modify numbers (e.g., $+$ ).
Boolean Operator: Uses logical criteria to compare values (e.g., $<$ or $AND$ ).
Real: A number that may include a decimal point (e.g., $11.2$ ).
Boolean: A data type representing only $TRUE$ or $FALSE$ .
String: A sequence of characters forming a word or sentence.
Casting: Forcing a value into a certain format (e.g., treating a number as a string).

Additional Programming Techniques and Robustness

String Manipulation: Processes for modifying strings, such as Concatenation (joining strings) or Slicing (splitting strings).
File Handling: Code interactions with files, including opening or writing data.
Database Terms: Record (a row of related info), Table (a group of records), and Field (a specific part of a record, like a name).
SQL (Structured Query Language): Language designed specifically for database management.
Array: A set of data items stored together under a single name.
Sub Program: A smaller part of a program for a specific task. Includes Functions (return a value) and Procedures (do not always return a value).
Defensive Design: Prioritizing security, maintenance, and robustness during coding.
Authentication: Requiring factors like passwords or fingerprints for access.
Input Validation: Comparing entered data to rules to ensure it is valid before processing.
Maintainability: The ease of updating code, fixing bugs, and adding features. Enhanced by Naming Conventions, Indentation, and Comments.

Testing and Boolean Logic

Iterative Testing: Carried out during development.
Final Testing: Carried out at the end of development before release.
Syntax Error: An error breaking programming language rules, preventing the code from running.
Logic Error: Code runs but produces unexpected output.
Test Data Types:
- Normal Data: Data the program should accept.
- Boundary Data: Data at the extremes of acceptability.
- Invalid Data: Correct type but invalid value.
- Erroneous Data: Wrong data type.
AND Gate: Outputs $1$ only if both inputs are $1$ .
OR Gate: Outputs $1$ if at least one input is $1$ .
NOT Gate: Outputs the opposite of the single input.
Truth Table: Shows all possible input/output values for logic gates.

Languages and IDEs

High-Level Language: Closer to English, easier to learn (e.g., Python).
Low-Level Language: Closer to machine code, harder to understand.
Translator: Software converting programming code into machine code. Includes Compilers (converts in one go) and Interpreters (converts line by line).
Integrated Development Environment (IDE): Software for developers containing Editors, Error Diagnostics, and Runtime Environments.