GCSE Computer Science: End-of-Term Revision Guide | GCSE 计算机：期末复习提纲

📚 GCSE Computer Science: End-of-Term Revision Guide | GCSE 计算机：期末复习提纲

This revision guide covers the essential topics for GCSE Computer Science, helping you consolidate your understanding before the exam. Use it to self-assess and target your revision on areas that need the most attention.

本复习提纲涵盖 GCSE 计算机科学的核心主题，帮助你在考试前巩固理解。用它来自我评估，并针对最需要关注的领域进行复习。

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1. Computer Systems Architecture | 计算机系统架构

The CPU is the central processing unit, consisting of the Control Unit (CU), Arithmetic Logic Unit (ALU), and registers such as the Program Counter (PC), Memory Address Register (MAR), and Memory Data Register (MDR).

CPU 是中央处理器，由控制单元（CU）、算术逻辑单元（ALU）以及程序计数器（PC）、内存地址寄存器（MAR）和内存数据寄存器（MDR）等寄存器组成。

The von Neumann architecture stores both instructions and data in the same memory, using a shared bus system to transfer information between components.

冯·诺依曼架构将指令和数据存储在同一内存中，使用共享总线系统在组件之间传输信息。

The fetch-decode-execute cycle describes how the CPU processes instructions: fetch an instruction from memory into the MAR and MDR, decode what needs to be done, then execute the operation using the ALU if required.

取指-解码-执行周期描述了 CPU 如何处理指令：从内存取指令到 MAR 和 MDR，解码需要做什么，然后必要时用 ALU 执行操作。

CPU performance is affected by clock speed (cycles per second, measured in GHz), the number of cores, and the size and level of cache memory. Higher values generally give faster processing.

CPU 性能受时钟速度（每秒周期数，以 GHz 为单位）、核心数量以及缓存大小和层级的影响。数值越高通常处理速度越快。

An embedded system is a computer system with a dedicated function built into a larger mechanical or electronic system, e.g., a washing machine controller, microwave timer, or car engine management unit. It is often energy efficient and low cost.

嵌入式系统是内置于更大机械或电子系统中具有专用功能的计算机系统，例如洗衣机控制器、微波炉定时器或汽车引擎管理单元。它通常节能且成本低。

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2. Memory and Storage | 内存与存储

RAM (Random Access Memory) is volatile memory used to store data and instructions currently in use by the CPU. Its contents are lost when power is turned off.

RAM（随机存取内存）是易失性内存，用于存储 CPU 当前使用的数据和指令。断电后其内容会丢失。

ROM (Read-Only Memory) is non-volatile and stores the BIOS or firmware needed to boot the computer. It retains data without power.

ROM（只读存储器）是非易失性的，存储启动计算机所需的 BIOS 或固件。它在无电时仍能保留数据。

Virtual memory uses part of the hard disk or SSD as an extension of RAM when physical RAM is full. It is much slower than actual RAM and can cause performance issues (thrashing) if overused.

当物理 RAM 满时，虚拟内存使用硬盘或 SSD 的一部分作为 RAM 的扩展。它比实际 RAM 慢得多，如果过度使用可能导致性能问题（抖动）。

Secondary storage can be magnetic (HDD), optical (CD, DVD, Blu-ray), or solid-state (SSD, USB flash drives). When choosing, compare capacity, speed, portability, durability, reliability, and cost per unit of storage.

二级存储可以是磁性的（HDD）、光学的（CD、DVD、蓝光）或固态的（SSD、U盘）。选择时需比较容量、速度、便携性、耐用性、可靠性和单位存储成本。

Storage units: bit, nibble (4 bits), byte (8 bits), kilobyte KB (1000 bytes), megabyte MB (1000 KB), gigabyte GB (1000 MB), terabyte TB (1000 GB). Remember in exams the convention is 1 kilobyte = 1000 bytes (not 1024).

存储单位：比特（bit）、半字节（nibble，4 比特）、字节（byte，8 比特）、千字节 KB（1000 字节）、兆字节 MB（1000 KB）、千兆字节 GB（1000 MB）、太字节 TB（1000 GB）。记住考试中 1 KB = 1000 字节（而非 1024）。

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3. Data Representation | 数据表示

Binary is the base-2 number system. All digital data is ultimately stored as sequences of 0s and 1s. Each binary digit is a bit.

二进制是基数为 2 的数字系统。所有数字数据最终都以 0 和 1 的序列存储。每个二进制位是一个比特。

To convert binary to denary, add up the place values (1, 2, 4, 8, 16, 32, …) where a 1 appears. To convert denary to binary, repeatedly divide by 2 and write the remainders in reverse order.

将二进制转换为十进制，对出现 1 的位置的位值（1、2、4、8、16、32…）求和。将十进制转换为二进制，重复除以 2 并反向记录余数。

Hexadecimal (base-16) uses digits 0-9 and letters A-F. Each hex digit represents a nibble (4 bits). It makes binary more human-friendly. Convert by splitting binary into groups of 4 bits from the right.

十六进制（基数 16）使用数字 0-9 和字母 A-F。每个十六进制位代表一个半字节（4 位）。它使二进制更易于人阅读。转换时从右往左将二进制每 4 位为一组。

Character encoding: Standard ASCII uses 7 bits to represent 128 characters; extended ASCII uses 8 bits for 256. Unicode uses up to 32 bits per character to represent symbols from many writing systems, including emojis.

字符编码：标准 ASCII 使用 7 位表示 128 个字符；扩展 ASCII 使用 8 位表示 256 个。Unicode 每个字符最多使用 32 位，可以表示众多书写系统中的符号，包括表情符号。

Images are grids of pixels. Resolution = total pixels (width × height). Colour depth is the number of bits per pixel. Image file size (in bits) = width × height × colour depth. More bits per pixel allow more colours.

图像由像素网格构成。分辨率 = 总像素（宽 × 高）。颜色深度是每像素位数。图像文件大小（比特）= 宽 × 高 × 颜色深度。每像素位数越多，可表示的颜色越多。

Sound is represented digitally by sampling the sound wave at regular intervals (sample rate in Hz) and assigning each sample a bit depth. Sound file size (bits) = sample rate × bit depth × duration (seconds). For stereo, multiply by 2.

声音通过以固定间隔（采样率，单位为 Hz）对声波采样并为每个样本分配位深度来数字化表示。音频文件大小（比特）= 采样率 × 位深度 × 时长（秒）。立体声还需乘以 2。

Compression reduces file size. Lossy compression permanently removes data (e.g., MP3, JPEG), sacrificing some quality. Lossless compression preserves the original data exactly (e.g., PNG, ZIP).

压缩可减小文件大小。有损压缩永久删减数据（如 MP3、JPEG），牺牲一定质量。无损压缩精确保留原始数据（如 PNG、ZIP）。

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4. Computer Networks | 计算机网络

A network connects two or more computers. A LAN (Local Area Network) covers a small building or campus; a WAN (Wide Area Network) spans cities or countries, such as the Internet.

网络连接两台或多台计算机。LAN（局域网）覆盖一栋建筑或校园；WAN（广域网）跨越城市或国家，例如互联网。

Star topology connects all devices to a central switch or hub. If one cable fails, only that node is affected, but the central device is a single point of failure.

星型拓扑将所有设备连接到中央交换机或集线器。如果一根线缆故障，只有该节点受影响，但中央设备是单点故障。

Mesh topology (full or partial) provides multiple connections between devices. It offers high reliability and redundancy, often used in backbone networks, but is expensive to cable.

网状拓扑（全连接或部分连接）在设备间提供多条连接。它可靠性高、有冗余，常用于骨干网络，但布线成本高。

Protocols are rules for communication. The TCP/IP model layers: Application (HTTP, FTP, SMTP, POP3/IMAP), Transport (TCP, UDP), Internet (IP), Network Access (Ethernet/Wi-Fi). TCP ensures reliable delivery; IP addresses and routes packets.

协议是通信规则。TCP/IP 模型分层：应用层（HTTP、FTP、SMTP、POP3/IMAP）、传输层（TCP、UDP）、互联网层（IP）、

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