📚 Year 11 Eduqas Computer Science: Core Knowledge Review | Year 11 Eduqas 计算机：核心知识点梳理
Welcome to this revision guide covering the essential topics for Eduqas GCSE Computer Science. We've distilled the key concepts into 12 digestible sections, pairing English and Chinese explanations to reinforce your understanding. Use this to consolidate your knowledge and prepare confidently for your assessments.
欢迎阅读这份针对 Eduqas GCSE 计算机科学的核心知识点梳理指南。我们将关键概念浓缩为12个易于消化的小节，每一点都提供中英双语解释，以强化你的理解。请用它来巩固知识，为考试做好充分准备。
1. Data Representation (Binary & Hexadecimal) | 数据表示（二进制与十六进制）
All data in a computer is stored and processed in binary – a base‑2 system using only the digits 0 and 1. Each binary digit is called a bit.
计算机中的数据全部以二进制形式存储和处理——二进制是基数为2的系统，仅使用数字0和1。每个二进制数字称为一个比特。
4, 2¹=2, 2⁰=1. The binary number 1101₂ is therefore 1×8 + 1×4 + 0×2 + 1×1 = 13 in decimal.
二进制中的位值是2的幂：2³=8, 2²=4, 2¹=2, 2⁰=1。因此二进制数1101₂等于1×8 + 1×4 + 0×2 + 1×1 = 十进制13。
Hexadecimal (hex) uses base 16, with digits 0‑9 then A‑ bits (a nibble), making it a compact way to write binary. For example, 1111 0100₂ = F4₁₆.
十六进制使用基数16，数字为0‑9及A‑F。一个十六进制数字恰好代表4个比特（一个半字节），因此成为书写二进制的紧凑方式。例如1111 0100₂ = F4₁₆。
When adding binary numbers, a carry can occur. If a result exceeds the available bit width, an overflow occurs, which can lead to calculation errors.
二进制加法会产生进位。如果结果超过了可用的位宽，就会发生溢出，导致计算错误。
Character sets such as ASCII (7‑bits, 128 characters) and Unicode (up to 32‑bits) map characters to binary codes. Unicode can represent emojis and symbols from many languages.
字符集如ASCII（7位，128个字符）和Unicode（最多32位）将字符映射为二进制编码。Unicode可以表示表情符号以及多种语言的文字。
Images are stored as a grid of pixels, each assigned a binary colour value. Colour depth (bits per pixel) determines the number of available colours – 8‑bit colour gives 256 colours.
图像存储为像素网格，每个像素分配一个二进制颜色值。颜色深度（每像素位数）决定了可用的颜色数——8位颜色可表示256种颜色。
Sound is digitised by sampling the sound wave at regular intervals and quantising each sample to a binary number. Higher sample rate and bit depth improve quality but increase file size.
声音通过固定间隔采样波形并将每个样点量化为二进制数来数字化。更高的采样率和位深度能提升音质，但也会增大文件大小。
Lossless compression (e.g. run‑length encoding) reduces file size without losing any data. Lossy compression (e.g. JPEG, MP3) permanently discards some information to achieve much smaller files.
无损压缩（如行程编码）减小文件大小但不丢失任何数据。有损压缩（如JPEG、MP3）则永久丢弃部分信息来换取更小的文件。
2. Computer Architecture (CPU & Fetch-Execute Cycle) | 计算机体系结构（CPU与取指-执行周期）
The CPU (Central Processing Unit) houses the Arithmetic Logic Unit (ALU) for arithmetic and logic operations, and the Control Unit (CU) which orchestrates data movement and instruction execution.
CPU包含算术逻辑单元（ALU）用于运算，以及控制单元（CU）负责协调数据流动和指令执行。
Key registers: the Program Counter (PC) holds the address of the next instruction; the Memory Address Register (MAR) holds the address to be read/written; the Memory Data Register (MDR) holds the data; and the Accumulator (ACC) stores intermediate results.
关键寄存器：程序计数器（PC）存放下一条指令的地址；内存地址寄存器（MAR）存放待读/写的地址；内存数据寄存器（MDR）存放数据；累加器（ACC）存放中间结果。
During the fetch-execute cycle: the PC value is copied to the MAR, the instruction is fetched from memory into the MDR, the instruction is decoded, executed, and then the PC is incremented to point to the next instruction.
在取指-执行周期中：PC值被复制到MAR，从内存取指令到MDR，指令被解码并执行，随后PC递增指向下一条指令。
Clock speed (measured in GHz) indicates how many cycles the CPU can perform per second. Multi‑core CPUs contain multiple processing units, enabling true parallel execution. Cache is small, high‑speed memory that holds frequently used data and instructions.
时钟速度（以GHz为单位）表示CPU每秒可执行的周期数。多核CPU包含多个处理单元，可以实现真正的并行执行。缓存是容纳常用数据和指令的小容量高速存储器。
3. Memory and Storage | 存储器与存储设备
RAM (Random Access Memory) is volatile – it loses its contents when power is off. It stores the operating system, programs, and data currently in use. ROM is non‑volatile and typically holds the BIOS/firmware to boot the computer.
RAM（随机存取存储器）是易失性的——断电后内容丢失。它存放正在使用的操作系统、程序和数据。ROM是非易失性的，通常保存用于启动计算机的BIOS/固件。
When RAM is full, the OS can use part of the hard disk as virtual memory, swapping pages of data in and out. Virtual memory is much slower than physical RAM.
当RAM已满，操作系统可以利用部分硬盘空间作为虚拟内存，将数据页面换入换出。虚拟内存比物理RAM慢得多。
Secondary storage devices include magnetic HDDs, solid‑state drives (SSDs), and optical media. SSDs have no moving parts – they are faster, more resistant to shock, but generally cost more per gigabyte than HDDs.
二级存储设备包括磁介质硬盘（HDD）、固态硬盘（SSD）和光学介质。SSD没有机械部件——速度更快、更抗震，但每GB成本通常高于HDD。
e = 4 bits, 1 byte = 8 bits, 1 KB ≈ 1000 bytes, 1 MB ≈ 1000 KB, 1 GB ≈ 1000 MB, and so on.
存储单位：1半字节=4位，1字节=8位，1KB≈1000字节，1MB≈1000KB，1GB≈1000MB，以此类推。
4. Systems Software & Operating Systems | 系统软件与操作系统
The operating system (OS) manages hardware resources and provides services such as memory management, multitasking, peripheral management, file management, and a user interface (GUI or CLI).
操作系统管理硬件资源并提供服务，如内存管理、多任务处理、外设管理、文件管理和用户界面（图形界面或命令行）。
Utility software performs dedicated maintenance tasks: disk defragmentation, backup, encryption, anti‑malware scanning, and firewall configuration.
工具软件执行专门的维护任务：磁盘碎片整理、备份、加密、反恶意软件扫描和防火墙配置。
Firmware is low‑level software
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