📚 Pre-U OCR Computer Science: Rapid Memorisation Guide for Key Vocabulary & Terms | Pre-U OCR 计算机科学：关键词汇术语速记指南
Mastering the technical vocabulary of computer science is essential for success in the Pre-U OCR examination. This guide breaks down core terms into logical clusters, providing concise definitions and memorable associations that align with the syllabus. Whether you are revisiting abstract data types, computational theory, or system architecture, these structured techniques will help you internalise precise terminology quickly.
掌握计算机科学技术词汇是在 Pre-U OCR 考试中取得成功的关键。本指南将核心术语按逻辑分成若干聚类，提供简洁的定义和易于记忆的联想，并与教学大纲紧密结合。无论您是在复习抽象数据类型、计算理论还是系统架构，这些结构化的技巧都能帮助您迅速内化精确的术语。
1. Abstract Data Types (ADTs) | 抽象数据类型
An abstract data type is a model for data structures that defines the type solely by its operations, not by its implementation. Think of an ADT as a contract: it specifies what operations are possible (e.g. push, pop for a stack) without revealing how data is stored.
抽象数据类型是一种数据结构的模型，它仅通过操作来定义类型，而非通过实现方式。可以把 ADT 想象成一份契约：它规定了哪些操作可行（例如栈的 push、pop），而不暴露数据的存储方式。
The stack ADT follows Last-In-First-Out (LIFO) behaviour. Key operations include push, pop, and peek. Visualise a stack of plates; you can only add or remove from the top.
栈 ADT 遵循后进先出（LIFO）原则。关键操作包括压入、弹出和查看栈顶。想象一叠盘子，你只能从顶部添加或移走盘子。
In contrast, a queue ADT uses First-In-First-Out (FIFO). Operations: enqueue and dequeue. Picture a line at a bus stop; the first person to arrive is the first to board.
相比之下，队列 ADT 采用先进先出（FIFO）原则。操作：入队和出队。想象公交车站的排队队伍，最先到达的人最先上车。
The priority queue is a variant where each element has a priority value. Elements with higher priority are dequeued before those with lower priority, independently of arrival time. It is often implemented using a binary heap.
优先队列是一种变体，其中每个元素都有一个优先级值。高优先级元素会比低优先级元素优先出队，与到达时间无关。它通常使用二叉堆来实现。
Graphs and trees are non-linear ADTs. A tree is a hierarchical structure with a root node and child nodes, free of cycles. A graph is a set of vertices connected by edges, which may be directed or undirected. Remember: a tree is a connected acyclic graph.
图和树是非线性 ADT。树是一种层次结构，有根节点和子节点，且无环。图是由边连接的一组顶点构成的集合，边可以是有向或无向的。记住：树是连通的无环图。
2. Object-Oriented Programming (OOP) Pillars | 面向对象编程的支柱
Encapsulation means bundling data (attributes) and methods that operate on that data within a single unit (class), and restricting direct access to some of an object’s components. It is achieved via access modifiers like private and public. Think of a capsule: the medicine inside is protected and only accessible through the outer shell.
封装是指将数据（属性）和操作这些数据的方法捆绑在一个单元（类）中，并限制对对象某些组成部分的直接访问。它通过 private、public 等访问修饰符实现。想象一个胶囊：里面的药物受到保护，只能通过外壳才能接触。
Inheritance allows a class (subclass) to derive properties and behaviours from another class (superclass), promoting code reuse. Use the phrase ‘is-a’ relationship: a Dog is a Mammal. The subclass may override methods of the superclass to provide specific implementations.
继承允许一个类（子类）从另一个类（超类）派生出属性和行为，促进了代码重用。使用“是一个”关系来记忆：狗是哺乳动物。子类可以重写超类的方法以提供特定实现。
Polymorphism means ‘many forms’. It enables objects of different classes to be treated as objects of a common superclass. Method overriding (run-time polymorphism) and method overloading (compile-time polymorphism) are typical examples. The same method call can behave differently depending on the actual object type.
多态意味着“多种形态”。它使得不同类的对象可以被当作同一个公共超类的对象来处理。方法重写（运行时多态）和方法重载（编译时多态）是典型例子。同一个方法调用可以根据实际对象类型产生不同的行为。
Abstraction focuses on exposing only essential features and hiding unnecessary implementation details. Abstract classes and interfaces are mechanisms to enforce abstraction. An interface defines a set of method signatures that a class must implement, providing a ‘contract’ without dictating how.
抽象专注于仅暴露必要特性、隐藏不必要实现细节。抽象类和接口是强制实现抽象的机制。接口定义了一组方法签名，类必须实现这些方法，提供了一个“契约”而不规定具体做法。
3. Computational Complexity & Big O Notation | 计算复杂度与大 O 表示法
Big O notation describes the upper bound of an algorithm’s time or space requirements as the input size n grows. It focuses on the dominant term and ignores constants. For example, O(2n² + 3n) simplifies to O(n²). Visualise the steepness of a curve; constants only shift it, but the shape matters most.
大 O 表示法描述了随着输入规模 n 增大，算法所需时间或空间的上界。它关注主导项，忽略常数。例如，O(2n² + 3n) 简化为 O(n²)。想象一条曲线的陡峭程度；常数只会平移它，但形状才是最重要的。
Common complexities in ascending order: O(1) constant time – accessing an array element by index. O(log n) logarithmic time – binary search. O(n) linear time – traversing an array. O(n log n) linearithmic – efficient sorting algorithms like merge sort. O(n²) quadratic – simple bubble sort. O(2ⁿ) exponential – recursive Fibonacci without memoisation.
常见复杂度按升序排列：O(1) 常数时间——按索引访问数组元素。O(log n) 对数时间——二分查找。O(n) 线性时间——遍历数组。O(n log n) 线性对数时间——归并排序等高效排序算法。O(n²) 平方时间——简单冒泡排序。O(2ⁿ) 指数时间——无记忆化的递归斐波那契。
To memorise logarithmic complexity, recall that log₂(1024) = 10, meaning an algorithm that halves the problem each step can handle a billion-sized input in about 30 steps. That immense reduction is the hallmark of O(log n).
要记住对数复杂度，回想 log₂(1024) = 10，这意味着每一步将问题规模减半的算法，大约 30 步就能处理十亿级输入。这种巨大的缩减正是 O(log n) 的特征。
Space complexity follows the same notation but counts memory used. Recursive algorithms often incur O(n) space due to the call stack, while iterative versions may be O(1). Always consider both time and space when evaluating algorithms.
空间复杂度遵循相同的表示法，但统计使用的内存。递归算法通常因调用栈而耗费 O(n) 空间，而迭代版本可能只需 O(1)。评估算法时务必同时考虑时间和空间。
4. Sorting & Searching Algorithms | 排序与查找算法
Bubble sort repeatedly steps through the list, compares adjacent elements, and swaps them if they are in the wrong order. It has O(n²) time complexity but O(1) space. To recall its name, imagine larger elements ‘bubbling up’ to the end of the list with each pass.
冒泡排序反复遍历列表，比较相邻元素，若顺序错误则交换它们。其时间复杂度为 O(n²)，空间复杂度为 O(1)。联想其名称，想象较大元素随着每次遍历“冒泡”到列表末尾。
Merge sort uses a divide-and-conquer strategy: recursively split the list into halves, sort each half, then merge the sorted halves. Its time complexity is O(n log n) in all cases, but it requires O(n) extra space. It is stable and ideal for linked lists.
归并排序采用分治策略：递归地将列表分成两半，分别对每一半排序，然后合并已排序的两半。它在所有情况下的时间复杂度均为 O(n log n)，但需要 O(n) 额外空间。它稳定且非常适合链表。
Quick sort selects a pivot element and partitions the array so that elements less than the pivot come before it, and greater elements come after. Average time is O(n log n), but worst-case (poor pivot) is O(n²). Being in-place, its space complexity is O(log n) due to recursion. Recalling the word ‘pivot partition’ helps cement the mechanism.
快速排序选择一个基准元素，并将数组分区，使得小于基准的元素在其前，大于基准的在其后。平均时间复杂度为 O(n log n)，但最坏情况（糟糕的基准选择）为 O(n²)。由于原地排序，其空间复杂度因递归调用为 O(log n)。记住“基准分区”这一词组有助于牢固掌握机制。
Binary search operates on a sorted array by repeatedly dividing the search interval in half. Compare the target value to the middle element; if not equal, eliminate the half where the target cannot lie. Time complexity is O(log n). To memorise, link ‘binary’ with ‘halving’.
二分查找在有序数组上进行，通过反复将查找区间减半来操作。将目标值与中间元素比较；若不相等，则排除目标不可能出现的一半。时间复杂度为 O(log n)。为便于记忆，将“二分”与“折半”关联起来。
5. Operating System Fundamentals | 操作系统基础
The kernel is the core component of an OS, managing system resources like CPU, memory, and I/O devices. It runs in privileged mode (kernel space) and provides system calls for user programs. Think of the kernel as the conductor of an orchestra, coordinating every section without being visible to the audience.
内核是操作系统的核心组件，管理 CPU、内存和 I/O 设备等系统资源。它运行在特权模式（内核空间），并为用户程序提供系统调用。可以把内核想象成交响乐团的指挥，协调每个声部却不对观众现身。
Processes and threads: a process is an instance of a program in execution, having its own address space. A thread is a lightweight unit of execution within a process, sharing the process’s resources. Multiple threads allow concurrent execution but require careful synchronisation to avoid race conditions.
进程与线程：进程是正在执行的程序的实例，拥有自己的地址空间。线程是进程内的轻量级执行单元，共享进程的资源。多线程允许多个任务并发执行，但需要谨慎同步以避免竞态条件。
Virtual memory combines physical RAM with disk storage to create an illusion of a large, contiguous address space. Pages are moved between RAM and disk via paging. The page table maps virtual addresses to physical frames. A page fault occurs when the required page is not in memory, triggering a slow disk fetch.
虚拟内存将物理 RAM 与磁盘存储相结合，营造出巨大连续地址空间的假象。页通过分页机制在 RAM 和磁盘之间移动。页表将虚拟地址映射到物理帧。当所需页面不在内存中时会发生缺页，触发缓慢的磁盘读取。
Scheduling algorithms decide which process to run next. Round-robin assigns a fixed time quantum in a cyclic order. Priority scheduling picks the highest-priority process. Shortest-job-first reduces average waiting time. The mnemonic ‘RPS’ (Round-robin, Priority, Shortest) can recall common strategies.
调度算法决定接下来运行哪个进程。轮转调度按循环顺序分配固定时间片。优先级调度选择优先级最高的进程。最短作业优先可减少平均等待时间。助记词 ‘RPS’（轮转、优先级、最短）能忆起常见策略。
6. Data Representation & Binary Arithmetic | 数据表示与二进制算术
Two’s complement is the standard way to represent signed integers in binary. The most significant bit indicates sign (0 positive, 1 negative). To negate a number, invert all bits and add 1. This representation simplifies hardware because addition works uniformly for signed numbers.
补码（二进制补码）是表示有符号整数的标准方法。最高有效位表示符号（0 正，1 负）。求一个数的负数时，将所有位取反再加 1。此表示简化了硬件，因为加法对有符号数和无符号数同样适用。
Floating-point representation uses the form ± mantissa × 2^exponent (IEEE 754 standard). Single precision allocates 1 bit sign, 8 bits exponent (biased by 127), and 23 bits mantissa. Remember normalisation: the mantissa is adjusted so that its most significant bit is 1, maximising precision.
浮点表示采用 ± 尾数 × 2^指数（IEEE 754 标准）的形式。单精度分配 1 位符号、8 位指数（偏移 127）和 23 位尾数。记住规格化：调整尾数使得其最高有效位为 1，以最大化精度。
Binary addition follows simple rules: 0+0=0, 0+1=1, 1+1=0 carry 1, 1+1+1=1 carry 1. Overflow occurs when the result exceeds the representable range in the given bit width. For signed two’s complement, overflow can be detected when the carry into the sign bit differs from the carry out.
二进制加法遵循简单规则：0+0=0，0+1=1，1+1=0 进 1；1+1+1=1 进 1。当结果超出给定位宽的可表示范围时会发生溢出。对于有符号补码，当进入符号位的进位与离开符号位的进位不同时可检测到溢出。
Hexadecimal (base 16) provides a compact way to express binary. Digits 0-9 and letters A-F represent values 0 to 15. One hex digit corresponds to 4 binary bits (nibble). It is heavily used for memory addresses and colour codes, making lengthy binary sequences readable.
十六进制（基数为 16）提供了一种紧凑表达二进制的方式。数字 0-9 和字母 A-F 表示 0 至 15 的值。一个十六进制位对应 4 个二进制位（半字节）。它广泛用于内存地址和颜色编码，使长二进制序列变得可读。
7. Databases & SQL | 数据库与 SQL
A relational database organises data into tables (relations) with rows (tuples) and columns (attributes). Each table has a primary key that uniquely identifies each row. Foreign keys establish relationships between tables, enforcing referential integrity.
关系数据库将数据组织为表格（关系），包含行（元组）和列（属性）。每个表都有一个主键，用于唯一标识每一行。外键在表之间建立关系，强制引用完整性。
Normalisation is the process of reducing data redundancy and dependency by decomposing tables. 1NF requires atomic values and no repeating groups. 2NF eliminates partial dependencies on a composite key. 3NF removes transitive dependencies. ‘Every non-key attribute must depend on the key, the whole key, and nothing but the key’ is a classic mnemonic for 3NF.
规范化是通过分解表来减少数据冗余和依赖的过程。1NF 要求原子值且无重复组。2NF 消除对组合键的部分依赖。3NF 移除传递依赖。“每个非键属性必须依赖于键、整个键、且只依赖于键”是记忆 3NF 的经典口诀。
SQL (Structured Query Language) uses declarative commands. SELECT retrieves data; INSERT adds rows; UPDATE modifies; DELETE removes. The WHERE clause filters rows, JOIN combines tables based on matching columns. GROUP BY aggregates data, and HAVING filters groups.
SQL（结构化查询语言）使用声明式命令。SELECT 检索数据；INSERT 添加行；UPDATE 修改；DELETE 删除。WHERE 子句过滤行，JOIN 基于匹配列组合表。GROUP BY 聚合数据，HAVING 过滤分组。
ACID properties guarantee reliable database transactions: Atomicity (all or nothing), Consistency (database remains valid), Isolation (transactions do not interfere), Durability (committed data persists). Think of a bank transfer – it must either complete fully or not happen, ensuring no money vanishes.
ACID 特性保障可靠数据库事务：原子性（全有或全无）、一致性（数据库保持有效）、隔离性（事务互不干扰）、持久性（已提交数据永久保存）。想象银行转账——它要么完全完成，要么不发生，确保资金不会消失。
8. Networking & the TCP/IP Stack | 网络与 TCP/IP 协议栈
The TCP/IP model comprises four layers: Application (HTTP, SMTP, DNS), Transport (TCP, UDP), Internet (IP), and Network Access (Ethernet, Wi-Fi). Data is encapsulated with headers at each layer as it moves down the stack and de-encapsulated on receipt.
TCP/IP 模型包含四层：应用层（HTTP、SMTP、DNS）、传输层（TCP、UDP）、互联网层（IP）和网络接入层（以太网、Wi-Fi）。数据沿协议栈向下传递时，每层都会添加头部进行封装，接收时再逐层解封装。
IP addressing (IPv4) uses 32-bit addresses, often written in dotted-decimal notation. Subnet masks determine the network and host portions. Routers use IP addresses to forward packets across different networks.
IP 寻址（IPv4）使用 32 位地址，通常以点分十进制表示。子网掩码确定网络部分和主机部分。路由器使用 IP 地址在不同网络之间转发数据包。
TCP (Transmission Control Protocol) provides reliable, connection-oriented delivery with error checking, sequencing, and flow control. A three-way handshake (SYN, SYN-ACK, ACK) establishes a connection. UDP is connectionless and offers no guarantees, trading reliability for speed – suitable for streaming.
TCP（传输控制协议）提供可靠、面向连接的交付，具有差错校验、排序和流量控制功能。三次握手（SYN、SYN-ACK、ACK）建立连接。UDP 是无连接的，不提供保证，以可靠性换取速度——适合流媒体。
HTTP is a request-response protocol at the application layer. GET retrieves a resource; POST submits data. HTTPS adds a security layer via TLS/SSL, providing encryption and authentication. Remember: ‘S’ stands for secure, encrypting traffic to prevent eavesdropping.
HTTP 是应用层的请求-响应协议。GET 检索资源；POST 提交数据。HTTPS 通过 TLS/SSL 增加安全层，提供加密和认证。记住：’S’ 代表安全，加密流量以防止窃听。
9. Automata & Formal Languages | 自动机与形式语言
A finite state machine (FSM) consists of a finite set of states, a start state, an input alphabet, and a transition function. It is a model of computation used to design sequential logic and pattern matching. Mealy machines produce outputs on transitions; Moore machines associate outputs with states.
有限状态机（FSM）由有限状态集、起始状态、输入字母表和转移函数构成。这是一种用于设计时序逻辑和模式匹配的计算模型。米利机在转移时产生输出；摩尔机将输出与状态关联。
A Turing machine is a more powerful abstract machine consisting of a tape, a head, a state register, and a transition table. It can simulate any algorithmic computation. The Church-Turing thesis posits that anything effectively computable can be computed by a Turing machine.
图灵机是一种更强大的抽象机器，由一条纸带、一个读写头、一个状态寄存器和一张转移表构成。它可以模拟任何算法计算。邱奇-图灵论题认为，任何可有效计算的问题都可以由图灵机计算。
Regular languages are the simplest class of formal languages, accepted by finite automata and described by regular expressions. Context-free languages are accepted by pushdown automata (PDA) and described by context-free grammars. Context-sensitive and recursively enumerable languages form higher layers in the Chomsky hierarchy.
正则语言是最简单的形式语言类，被有限自动机接受，并由正则表达式描述。上下文无关语言被下推自动机（PDA）接受，由上下文无关文法描述。上下文相关语言和递归可枚举语言构成了乔姆斯基层级中的更高层次。
A regular expression uses symbols *, +, ., |, and brackets to define search patterns. For instance, a(b|c)* matches ‘a’ followed by zero or more ‘b’ or ‘c’ characters. Lexical analysers in compilers heavily rely on regular expressions to scan source code tokens.
正则表达式使用符号 *、+、.、| 和括号来定义搜索模式。例如，a(b|c)* 匹配 ‘a’ 后跟零个或多个 ‘b’ 或 ‘c’ 字符。编译器中的词法分析器大量依赖正则表达式来扫描源代码记号。
10. Security & Encryption | 安全与加密
Symmetric encryption uses a single shared key for both encryption and decryption. AES and DES are common algorithms. The main challenge is secure key distribution. Imagine a locked box that both sender and receiver can open using identical copies of a key.
对称加密使用单一共享密钥进行加密和解密。AES 和 DES 是常见算法。主要挑战是安全的密钥分发。想象一个锁着的盒子，发送方和接收方都能用钥匙的相同副本来打开。
Asymmetric encryption employs a key pair: a public key for encryption and a private key for decryption. RSA is a widely used algorithm. It solves the key exchange problem: anyone can encrypt using the public key, but only the holder of the private key can decrypt.
非对称加密使用一对密钥：公钥用于加密，私钥用于解密。RSA 是一种广泛使用的算法。它解决了密钥交换问题：任何人都可以使用公钥加密，但只有私钥持有者才能解密。
Hashing is a one-way function that converts input data into a fixed-size string of bytes. SHA-256 is a cryptographic hash function. Properties: deterministic, preimage resistant, collision resistant, and avalanche effect. Use the phrase ‘digest, not decryption’ to recall that hashes cannot be reversed.
哈希是一种单向函数，将输入数据转换为固定大小的字节串。SHA-256 是一种密码学哈希函数。特性：确定性、抗原像、抗碰撞和雪崩效应。用“摘要，非解密”这句话来记住哈希不可逆。
Digital signatures combine hashing and asymmetric encryption to verify authenticity and integrity. A sender signs a document by encrypting its hash with their private key; the receiver decrypts it with the sender’s public key and compares hashes. Non-repudiation is ensured.
数字签名结合了哈希和非对称加密，用于验证真实性和完整性。发送者通过用自己的私钥加密文档的哈希来签名；接收者用发送者的公钥解密并比对哈希。不可否认性得到保证。
11. Boolean Algebra & Logic Gates | 布尔代数与逻辑门
Boolean algebra operates on binary variables with values 0 and 1. Basic operations: AND (conjunction, A·B), OR (disjunction, A+B), NOT (negation, A’). De Morgan’s laws state that (A·B)’ = A’ + B’ and (A+B)’ = A’·B’. These laws allow conversion between sum-of-products and product-of-sums forms.
布尔代数对取值为 0 和 1 的二元变量进行运算。基本运算：与（合取，A·B）、或（析取，A+B）、非（否定，A’）。德摩根定律指出 (A·B)’ = A’ + B’ 以及 (A+B)’ = A’·B’。这些定律可以在积之和与和之积形式之间转换。
Logic gates are the physical implementations of Boolean functions. Common gates: AND, OR, NOT, NAND, NOR, XOR, XNOR. NAND and NOR are universal gates because any Boolean function can be implemented using only one of them. Think of ‘universal’ as ‘can build everything’.
逻辑门是布尔函数的物理实现。常见门：与、或、非、与非、或非、异或、同或。与非和或非是通用门，因为任何布尔函数都可以仅使用其中一种来实现。联想“通用”即“能构建一切”。
A half adder adds two bits, producing a sum bit and a carry bit. It consists of an XOR gate for sum and an AND gate for carry. A full adder adds three bits (two inputs plus carry-in), enabling multi-bit addition when cascaded. The distinction is simple: half lacks carry-in, full includes it.
半加器将两个位相加，产生一个和位和一个进位位。它由一个异或门（产生和）和一个与门（产生进位）构成。全加器将三个位（两个输入加进位输入）相加，级联后可实现多位加法。区别很简单：半加器缺少进位输入，全加器包含之。
Karnaugh maps (K-maps) are a visual method to simplify Boolean expressions, minimising the number of logic gates. Group adjacent 1s in powers of 2 to identify common variables. The simpler the expression, the more efficient the circuit.
卡诺图是一种可视化简化布尔表达式的方法，可最小化逻辑门数量。以 2 的幂次将相邻的 1 分组，以识别公共变量。表达式越简单，电路效率越高。
12. Ethical, Legal & Environmental Issues | 伦理、法律与环境问题
The Data Protection Act governs the collection, storage, and processing of personal data. Principles include data minimisation, purpose limitation, accuracy, and security. Individuals have rights to access, rectify, and erase their data. ‘Privacy by design’ is a key concept in modern regulations.
《数据保护法》管辖个人数据的收集、存储和处理。原则包括数据最小化、目的限制、准确性和安全性。个人有权访问、更正和删除其数据。“设计即隐私”是现代法规中的关键概念。
Computer misuse laws criminalise unauthorised access to computer systems, unauthorised access with intent to commit further offences, and unauthorised acts with intent to impair operation (e.g. malware distribution). The three tiers can be recalled as ‘access, intent, impairment’.
计算机滥用法将未经授权访问计算机系统、为了进一步犯罪而未经授权访问、以及蓄意损害运行的未经授权行为（如传播恶意软件）定为刑事犯罪。这三级可用“访问、意图、损害”来记忆。
Automated decision-making raises ethical concerns about bias, accountability, and transparency. A neural network can produce discriminatory outcomes if trained on biased data. The term ‘algorithmic fairness’ describes efforts to make decisions equitable and explainable.
自动化决策引发关于偏见、问责和透明度的伦理关切。如果神经网络基于有偏见的数据进行训练，可能产生歧视性结果。“算法公平性”这一术语描述了使决策变得公正和可解释的努力。
Green computing addresses the environmental impact of technology. Strategies include server virtualisation to reduce hardware footprints, algorithmic efficiency to use fewer CPU cycles, and responsible e-waste disposal. Think ‘reduce, reuse, recycle’ applied to digital devices and data centres.
绿色计算解决技术对环境的影响。策略包括：服务器虚拟化以减少硬件占地，提高算法效率以使用更少的 CPU 周期，以及负责任的电子垃圾处理。将“减少、重用、回收”应用于数字设备和数据中心。
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