📚 AS CAIE Computer Science: Key Terminology Quick-Study Guide | AS CAIE 计算机：词汇术语速记指南
Welcome to your fast-track revision resource for AS CAIE Computer Science. Mastering the subject is not just about understanding concepts; it requires a solid command of the precise terminology used in examination questions. This guide breaks down essential vocabulary into logical sections, pairing each term with a clear explanation and a memorable shortcut to help you recall it under pressure. Use these pairings to test yourself regularly and build confidence for your exams.
欢迎使用你的 AS CAIE 计算机科学快速复习资源。掌握这门学科不仅要理解概念，还需要牢固掌握考试题目中使用的准确术语。本指南将核心词汇按逻辑章节分类，为每个术语配上清晰的解释和一个易于记忆的诀窍，帮助你在压力下快速回想。请定期用这些成对的内容自测，为考试树立信心。
1. Data Representation Core Terms | 数据表示核心术语
A bit (binary digit) is the smallest unit of data and stores either 0 or 1. A nibble is a group of 4 bits, and a byte is 8 bits. Memory sizes use prefixes such as kilobyte (KB) and megabyte (MB), but note that 1 KB = 210 bytes. The most significant bit (MSB) carries the largest weight in a binary number, while the least significant bit (LSB) represents the units value.
位(bit) 是最小数据单元，存 0 或 1。半字节(nibble)是 4 位，字节(byte)是 8 位。内存大小使用 KB、MB 等前缀，注意 1 KB = 210 字节。最高有效位(MSB) 权重最大，最低有效位(LSB) 是个位。速记：bit 是“binary digit”的缩写，nibble 就是咬一小口(半个 byte)，byte 一口吞下 8 位。
Binary (base-2) uses digits 0 and 1. Denary (decimal) is base-10. To convert binary to denary, multiply each bit by 2 raised to its position index (starting from 0 on the right). For hexadecimal (base-16), each digit 0–9 and A–F represents four binary bits, making it a very compact notation. For example, 1101 10112 becomes DB16.
二进制 (基2) 用 0,1；十进制基10。二进制转十进制：每位乘 2 的幂。十六进制 (基16) 每个数字 0-9、A-F 代表四个二进制位，非常紧凑。如 1101 10112 写成 DB16。口诀：每半字节 (nibble) 直接翻成一个十六进制字符。
During binary addition, if the result of adding two bits exceeds 1, a carry is generated. When the result of a calculation requires more bits than allocated storage, an overflow error occurs. In 8-bit arithmetic using two’s complement, the range of signed integers is -128 to +127. A negative number is represented by inverting all bits and adding 1; the MSB acts as the sign bit (1 for negative).
进行二进制加法时，结果超过 1 就产生进位。若结果超出分配的位数，发生溢出。采用补码表示有符号数时，8 位范围 -128 到 +127。负数的表示：全部位取反再加 1，MSB 为 1 表示负。助记：溢出就像杯子满了；取反加一叫“flip and add 1”。
Logic gates perform Boolean operations. AND outputs 1 only if all inputs are 1; OR outputs 1 if at least one input is 1; NOT inverts its single input; XOR (exclusive OR) outputs 1 when inputs differ. Truth tables help you verify these rules. These gates form the basis of digital circuits used inside the ALU.
逻辑门：AND 全 1 才 1，OR 有 1 就 1，NOT 取反，XOR 相异为 1。真值表能帮助你验证。逻辑门是 ALU 内部数字电路的基础。速记口诀：与门乘，或门加，非门翻，异或不同出 1。
Character sets map binary codes to symbols. ASCII (American Standard Code for Information Interchange) originally used 7 bits, later extended to 8 bits to include more symbols. Unicode uses variable-length encoding and can represent characters from all writing systems, making it essential for global software.
字符集 将二进制编码映射到符号。ASCII 初期用 7 位，后来扩展至 8 位。Unicode 使用变长编码，可表示所有文字符号，是国际化软件的基础。对比记忆：ASCII 像基础字母表，Unicode 是万国码。
2. Hardware and Processor Fundamentals | 硬件与处理器基础
The central processing unit (CPU) is the brain of a computer; it comprises the control unit (CU), the arithmetic logic unit (ALU), and a set of registers. Key registers include the program counter (PC) (address of next instruction), memory address register (MAR), memory data register (MDR), current instruction register (CIR), and accumulator (ACC). Buses (data bus, address bus, control bus) carry information between components.
中央处理器(CPU) 是电脑大脑，包含控制单元(CU)，算术逻辑单元(ALU)和寄存器组。关键寄存器：程序计数器(PC)存下条指令地址，内存地址寄存器(MAR)与数据寄存器(MDR)负责访问内存，当前指令寄存器(CIR)存正在执行的指令，累加器(ACC)存运算结果。总线(数据、地址、控制)传送信息。记忆：CU 是导播，ALU 是演员，寄存器是即时备忘录。
The fetch-decode-execute (FDE) cycle is the sequence that the CPU repeats billions of times per second. First the instruction is fetched from RAM into the CIR, then the CU decodes it, and finally the appropriate unit executes it. The cycle speed is governed by the clock speed measured in hertz; multiple cores allow parallel execution, and cache provides high-speed memory directly on the CPU.
取指-译码-执行(FDE)周期 是 CPU 每秒重复数十亿次的步骤：从内存取到 CIR，CU 译码，然后执行。周期速度由时钟频率(Hz)决定；多核可同时执行多条指令；缓存是 CPU 内部的高速暂存区。联想：时钟是心跳，多核是多个厨师同时做菜，缓存是案板大小，越大越方便。
In the von Neumann architecture, both data and program instructions share the same memory, and processing is sequential. This differs from Harvard architecture, but at AS level the focus is on the stored-program concept. Embedded systems are dedicated computers built into devices like washing machines; they have limited resources and run one specific program, often stored in ROM.
冯·诺依曼架构中，数据和程序指令共享同一内存，处理是顺序的，强调存储程序的概念。嵌入式系统是专用于洗衣机等设备的计算机，资源有限，只运行特定程序，常存储在 ROM 中。助记：通用 CPU 像瑞士军刀，嵌入式像专一工具。
3. Memory and Storage | 内存与存储
RAM (Random Access Memory) is volatile; its contents are lost when power is removed. It stores the programs and data currently in use. ROM (Read Only Memory) is non-volatile and holds the bootstrap loader (BIOS) that starts the computer. Virtual memory uses a portion of the hard drive as an extension of RAM when physical memory is full, but it is much slower.
RAM 易失性，断电内容丢失，存当前运行的程序和数据。ROM 非易失，存引导程序(BIOS)。虚拟内存 是物理内存不足时拿硬盘空间充当内存，但速度极慢。记忆：RAM 像白板，关机就擦净；ROM 像刻在石碑上的指令。
Secondary storage devices keep data permanently. HDDs use magnetic platters; they offer high capacity at low cost but have moving parts. SSDs use flash memory with no moving parts, giving faster access and greater durability but a higher cost per gigabyte. Optical discs (CD, DVD) use lasers. Cloud storage saves data on remote servers accessed via the internet, providing convenience and automatic backup.
辅助储存 永久保存数据。HDD 用磁性盘片，容量大价格低但有机械运动。SSD 闪存无运动部件，访问快更耐用但贵。光盘用激光。云存储把数据存网路上远程服务器，方便且自动备份。关键区分：速度 VS 容量 VS 成本。
| Storage Type | Volatile? | Speed | Typical Use |
|---|---|---|---|
| RAM | Yes | Very fast | Running applications |
| ROM | No | Fast | Firmware / bootloader |
| SSD | No | Fast | Long-term storage |
| HDD | No | Moderate | Mass storage |
4. Operating Systems and Interrupts | 操作系统与中断
The operating system (OS) acts as a bridge between user, application software and hardware. It handles memory management (allocating RAM), multitasking, file management, user interface, and security. An interrupt is a signal to the CPU that an event requires immediate attention, such as a key press or a disk completing a read request.
操作系统(OS) 是用户、软件与硬件间的桥梁。负责内存管理、多任务、文件管理、接口和安全。中断 是通知 CPU 需要立即处理的信号，比如按键或磁盘读完数据。大脑比喻：OS 是秘书，中断是紧急敲门。
When an interrupt occurs, the CPU suspends the current task, saves its state (registers and PC), and loads the address of the interrupt service routine (ISR). After the ISR finishes, the saved state is restored and the original task resumes. Hardware interrupts come from external devices; software interrupts are generated by programs, often to request OS services.
中断发生时，CPU 挂起当前任务，保存状态(寄存器和 PC)，并加载中断服务程序(ISR)的地址。ISR 结束后恢复现场继续原任务。硬件中断来自外部设备，软件中断由程序产生以请求 OS 服务。流程简记：暂停→保存→处理→恢复。
5. Networks and Communication | 网络与通信
A LAN (Local Area Network) connects computers in a small geographical area using cables or Wi-Fi. A WAN (Wide Area Network) connects LANs over large distances, often using leased telecommunications lines. In a client-server model, powerful servers provide shared resources, whereas in a peer-to-peer network each computer acts as both client and server.
局域网(LAN) 覆盖小范围，用网线或 Wi-Fi。广域网(WAN) 长距离连接多个 LAN。客户-服务器模型由强大服务器提供共享资源；对等网络中各电脑既是客户端又是服务器。联想：LAN 是家庭，WAN 是跨城市，客户-服务器像餐厅(服务员与厨房)，P2P 像朋友间直接分享。
Key network hardware includes routers (forward data between networks using IP addresses), switches (connect devices within a LAN and forward frames based on MAC addresses), NICs (network interface cards), and wireless access points (WAPs). A MAC address is a unique 48-bit hardware identifier; an IP address is a logical identifier used for routing across networks.
关键网络硬件：路由器 用 IP 地址在不同网络间转发数据；交换机 根据 MAC 地址在同一 LAN 内转发帧；网卡(NIC)；无线接入点(WAP)。MAC 地址 是 48 位硬件唯一标识；IP 地址 是
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