📚 Year 9 OCR Computer Science: Core Knowledge Review | Year 9 OCR 计算机：核心知识点梳理
Year 9 is the foundation year for the OCR GCSE Computer Science course. It is essential to grasp the key concepts in hardware, data representation, algorithms, programming, networks and the wider impact of technology. This article summarises the core knowledge areas you will encounter, providing clear explanations in both English and Chinese to support your revision.
九年级是 OCR GCSE 计算机科学课程的打基础之年。掌握硬件、数据表示、算法、编程、网络以及技术广泛影响中的关键概念至关重要。本文梳理了你将接触到的核心知识领域，并以中英双语提供清晰解释，助力你的复习。
1. Systems Architecture and the CPU | 系统架构与中央处理器
The Central Processing Unit (CPU) processes all instructions and data inside a computer. It follows the fetch-decode-execute cycle for every instruction. Key components include the Control Unit (CU) which directs operations, the Arithmetic Logic Unit (ALU) which performs calculations and logical decisions, and registers like the Program Counter (PC), Memory Address Register (MAR) and Memory Data Register (MDR).
中央处理器（CPU）处理计算机内的所有指令和数据。它针对每条指令遵循取指-解码-执行周期。关键部件包括指挥操作的控制单元（CU）、执行计算和逻辑决策的算术逻辑单元（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。
The Von Neumann architecture stores both program instructions and data in the same main memory. The CPU accesses memory through three buses: the address bus (carries memory locations), the data bus (carries the actual data), and the control bus (carries command signals).
冯·诺依曼架构将程序指令和数据存储在同一主存中。CPU通过三组总线访问内存：地址总线（传输内存地址）、数据总线（传输实际数据）和控制总线（传输命令信号）。
Clock speed, measured in hertz, determines how many fetch-decode-execute cycles can be performed per second. A higher clock speed generally means faster processing, but it also generates more heat. Cache memory is very fast memory located inside or near the CPU that stores frequently used instructions.
时钟速度以赫兹为单位，决定了每秒可执行多少个取指-解码-执行周期。时钟速度越高通常意味着处理速度越快，但也会产生更多热量。缓存是位于CPU内部或附近的高速存储器，用于存放频繁使用的指令。
2. Memory and Storage | 内存与存储设备
Primary memory includes RAM (Random Access Memory) and ROM (Read Only Memory). RAM is volatile, meaning it loses its data when power is turned off; it stores the operating system, programs and data currently in use. ROM is non-volatile and typically stores the boot program (BIOS) needed to start the computer.
主存包括随机存取存储器（RAM）和只读存储器（ROM）。RAM是易失性的，即断电后数据丢失；它存储当前正在使用的操作系统、程序和数据。ROM是非易失性的，通常存储启动计算机所需的引导程序（BIOS）。
Secondary storage is non-volatile and provides long-term data retention. Common types are magnetic hard disk drives (HDDs), solid state drives (SSDs) which are faster and more durable because they have no moving parts, and optical discs like CDs and DVDs. Storage capacity is measured in bytes, with units like kilobyte (KB), megabyte (MB), gigabyte (GB) and terabyte (TB).
辅助存储器是非易失性的，提供长期数据保存。常见类型包括磁性硬盘驱动器（HDD）、由于没有移动部件而更快更耐用的固态驱动器（SSD），以及CD和DVD等光盘。存储容量以字节为单位，单位有千字节（KB）、兆字节（MB）、吉字节（GB）和太字节（TB）。
| Unit | Equivalent |
|---|---|
| 1 bit | single binary digit (0 or 1) |
| 1 nibble | 4 bits |
| 1 byte | 8 bits |
| 1 KB | approx 1000 bytes |
| 1 MB | approx 1000 KB |
Data storage units
数据存储单位如上表。
3. Data Representation – Binary and Hexadecimal | 数据表示——二进制与十六进制
e, the binary number 1010 represents (1 × 2³) + (0 × 2²) + (1 × 2¹) + (0 × 2⁰) = 8 + 0 + 2 + 0 = 10 in denary.
计算机使用二进制（基数为2），因为晶体管有两种状态：开（1）和关（0）。二进制数由位组成。例如，二进制数1010表示 (1 × 2³) + (0 × 2²) + (1 × 2¹) + (0 × 2⁰) = 8 + 0 + 2 + 0 = 10（十进制）。
, then A=10, B=11, C=12, D=13, E=14, F=15. For example, binary 1101 1010 can be written as DA in hex.
十六进制（基数为16）常作为二进制数值的简写形式。每个十六进制数字代表四位（一个半字节）。使用数字0-9，然后A=10, B=11, C=12, D=13, E=14, F=15。例如，二进制1101 1010可以写成十六进制的DA。
and note remainders: 42 → 101010₂. Then group into nibbles 0010 1010, which is 2A in hex.
在十进制、二进制和十六进制之间转换是一项基本技能。将十进制42转换为二进制，反复除以2并记录余数：42 → 101010₂。然后按四个一组划分为 0010 1010，十六进制即为2A。
4. Representing Text, Images and Sound | 文本、图像与声音的表示
Characters are represented in binary using character sets. ASCII uses 7 bits, representing 128 characters including English letters, digits and symbols. Extended ASCII uses 8 bits for 256 characters. Unicode is a much larger standard that supports multiple languages and emojis, often using up to 32 bits per character.
字符使用编码集以二进制表示。ASCII 使用7位，表示包括英文字母、数字和符号在内的128个字符。扩展 ASCII 使用8位表示256个字符。Unicode 是一个庞大得多的标准，支持多种语言和表情符号，每个字符通常使用多达32位。
Images are represented as a grid of pixels. In a bitmap, each pixel is assigned a binary code for its colour. Colour depth (bits per pixel) determines how many colours can be represented: 1 bit gives 2 colours, 8 bits give 256 shades. Higher resolution (more pixels) gives better detail but increases file size. Metadata stores width, height and colour depth.
图像表示为像素网格。在位图中，每个像素被赋予一个表示其颜色的二进制代码。颜色深度（每像素位数）决定了可表示的颜色数量：1位可产生2种颜色，8位可产生256种色阶。更高的分辨率（更多像素）提供更好的细节，但会增加文件大小。元数据存储宽度、高度和颜色深度。
Sound is analogue and must be converted to digital by sampling. The sound wave is measured at regular intervals (sample rate) and each sample is given a binary value (sample resolution). A higher sample rate and higher bit depth produce a more accurate representation but result in larger files. For example, CD quality uses 44.1 kHz and 16 bits.
声音是模拟的，必须通过采样转换为数字信号。声波按照固定间隔被测量（采样率），每个采样被赋予一个二进制值（采样分辨率）。更高的采样率和更高的位深度可产生更精确的声音表示，但会导致文件更大。例如，CD质量使用44.1 kHz和16位。
5. Algorithms and Problem Solving | 算法与问题解决
An algorithm is a step-by-step procedure to solve a problem. It must be unambiguous, have a clear start and end, and produce the correct output for all valid inputs. Computational thinking involves decomposition (breaking down a problem), pattern recognition, abstraction (ignoring unnecessary detail), and algorithm design.
算法是解决问题的分步过程。它必须明确无歧义，有清晰的起点和终点，并对所有有效输入产生正确输出。计算思维包括分解（拆分问题）、模式识别、抽象（忽略不必要细节）以及算法设计。
Algorithms can be expressed using flowcharts, which use standard symbols: oval for start/stop, parallelogram for input/output, rectangle for a process, and diamond for a decision. Pseudocode is a text-based way to describe an algorithm using plain English and some programming-like structures, without strict syntax.
算法可以用流程图表示，流程图使用标准符号：椭圆表示开始/结束，平行四边形表示输入/输出，矩形表示处理，菱形表示决策。伪代码是一种基于文本的描述算法方式，使用简单英语和一些类似编程的结构，无需严格的语法。
Sorting and searching algorithms are key. A linear search examines each item in a list until the target is found. A binary search works on a sorted list by repeatedly dividing it in half, much faster but requires the data to be sorted. Bubble sort repeatedly compares and swaps adjacent items to put the list in order.
排序和搜索算法是关键。线性搜索逐一检查列表中的每个项目，直到找到目标。二分搜索在有序列表中通过反复将其分成两半来工作，速度快得多，但要求数据已排序。冒泡排序反复比较并交换相邻项，将列表按顺序排列。
6. Programming Constructs and Data Types | 编程结构与数据类型
All programming languages rely on three basic constructs: sequence (instructions executed in order), selection (if-else statements that choose a path based on a condition), and iteration (loops). Iteration can be definite (for loop, repeats a known number of times) or indefinite (while loop, repeats while a condition is true).
所有编程语言都依赖三种基本结构：顺序（指令按顺序执行）、选择（根据条件选择路径的 if-else 语句）和迭代（循环）。迭代可以是确定性的（for 循环，重复已知次数）或非确定性的（while 循环，当条件为真时重复）。
Common data types include integer (whole numbers), real/float (numbers with decimals), Boolean (true/false), character (single letter or symbol), and string (a sequence of characters). Variables act as named storage locations; their data type determines what operations are allowed and how much memory is used.
常见数据类型包括整数（整数）、实数/浮点数（带小数点的数字）、布尔型（真/假）、字符（单个字母或符号）以及字符串（一串字符）。变量作为命名的存储位置；其数据类型决定了允许的操作以及使用的内存量。
+, -, *, /, MOD (remainder), DIV (integer division). Comparison operators: == (equal to), ! qual to), >, <, >=, <=. Logical operators: AND, OR, NOT, often used to combine conditions.
运算符用于对数据执行操作。算术运算符：+、-、*、/、MOD（取余）、DIV（整除）。比较运算符：==（等于）、!=（不等于）、>、<、>=、<=。逻辑运算符：AND、OR、NOT，常用于组合条件。
7. Network Fundamentals | 网络基础
A network is two or more computers connected together to share resources. A Local Area Network (LAN) covers a small geographical area, such as a school or office, and is usually owned by one organisation. A Wide Area Network (WAN) connects LANs over large distances, the internet being the largest WAN.
网络是将两台或多台计算机连接在一起以共享资源。局域网（LAN）覆盖较小地理区域，如学校或办公室，通常由一个组织拥有。广域网（WAN）连接大范围局域网，互联网就是最大的广域网。
Network hardware includes switches (connect devices in a LAN and send data only to the intended recipient), routers (connect different networks and direct data packets across the internet), and Network Interface Cards (NICs) that allow a device to connect. Transmission media can be wired (Ethernet copper, fibre optic) or wireless (Wi-Fi, Bluetooth).
网络硬件包括交换机（在局域网中连接设备并仅将数据发送到目标接收者）、路由器（连接不同网络并引导数据包通过互联网）以及允许设备连接的网络接口卡（NIC）。传输介质可以是有线（以太网铜缆、光纤）或无线（Wi-Fi、蓝牙）。
Common topologies include star (all devices connect to a central switch; if one cable fails, only that device is affected) and mesh (devices are interconnected, providing multiple paths and high reliability). Protocols are rules for communication, such as TCP/IP (responsible for reliable packet delivery), HTTP/HTTPS (web), FTP (file transfer) and SMTP (email sending).
常见拓扑结构包括星型（所有设备连接到中央交换机；一条线路故障只影响该设备）和网状（设备相互连接，提供多条路径和高可靠性）。协议是通信规则，例如 TCP/IP（负责可靠的数据包传送）、HTTP/HTTPS（网页）、FTP（文件传输）和 SMTP（邮件发送）。
8. Cybersecurity Threats and Prevention | 网络安全威胁与防护
Malware is malicious software designed to damage or gain unauthorised access. Types include viruses (attach to files and spread), worms (self-replicate across networks), trojans (disguised as legitimate software), and ransomware (encrypts files and demands a payment). Phishing involves fraudulent emails or messages tricking users into revealing personal information.
恶意软件是旨在破坏或获得未经授权访问的恶意软件。类型包括病毒（附加到文件并传播）、蠕虫（在网络上自我复制）、特洛伊木马（伪装成合法软件）和勒索软件（加密文件并要求付款）。网络钓鱼涉及欺诈性电子邮件或消息，诱骗用户透露个人信息。
Social engineering exploits human psychology rather than technical weaknesses. For example, a blagger might impersonate someone to gain confidential information. To reduce risks, organisations use firewalls (filter incoming and outgoing traffic), anti-malware software, and regular software updates to patch vulnerabilities.
社会工程学利用人类心理而非技术弱点。例如，欺诈者可能冒充他人以获取机密信息。为降低风险，组织使用防火墙（过滤进出流量）、反恶意软件，并定期进行软件更新以修补漏洞。
Encryption scrambles data so it can only be read by someone with the correct key. It is essential for securing data in transit (e.g., HTTPS uses SSL/TLS encryption). Strong passwords, two-factor authentication and access rights further protect data from unauthorised access.
加密将数据打乱，只有拥有正确密钥的人才能读取。这对于保护传输中的数据至关重要（例如，HTTPS 使用 SSL/TLS 加密）。强密码、双因素认证和访问权限进一步保护数据免受未经授权的访问。
9. Logic Gates and Boolean Logic | 逻辑门与布尔逻辑
Logic gates are the building blocks of digital circuits. They take one or more binary inputs and produce a single binary output. The three basic gates are AND, OR and NOT. The AND gate outputs 1 only if all inputs are 1. The OR gate outputs 1 if at least one input is 1. The NOT gate inverts its input (1 becomes 0, 0 becomes 1).
逻辑门是数字电路的构建模块。它们接受一个或多个二进制输入并产生单个二进制输出。三种基本门是 AND、OR 和 NOT。AND门仅当所有输入为1时才输出1。OR门如果至少一个输入为1就输出1。NOT门反转其输入（1变0，0变1）。
| A | B | A AND B | A OR B |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 1 |
Truth table for AND and OR gates
AND和OR门的真值表如上。
Boolean expressions can be simplified and combined. NAND (NOT AND) and NOR (NOT OR) gates are universal, meaning any logic circuit can be built using only NAND gates. Understanding logic helps in designing circuits and writing conditions in programs.
布尔表达式可以简化和组合。与非门（NAND）和或非门（NOR）是通用门，意味着仅使用与非门即可构建任何逻辑电路。理解逻辑有助于设计电路和在程序中编写条件。
10. Legal and Ethical Issues in Computing | 计算机中的法律与伦理问题
The use of computers is governed by laws that protect individuals and data. The Data Protection Act (2018) controls how personal data is collected, used and stored, giving individuals rights to access their data. The Computer Misuse Act (1990) makes it illegal to gain unauthorised access to computers, including hacking and spreading malware.
计算机的使用受到保护个人和数据的法律约束。《数据保护法》（2018）规范个人数据的收集、使用和存储方式，赋予个人访问其数据的权利。《计算机滥用法》（1990）将未经授权访问计算机（包括黑客攻击和传播恶意软件）定为非法。
Copyright and intellectual property laws protect creators' rights. Software piracy, downloading copyrighted content without permission, and plagiarism are illegal. The Copyright, Designs and Patents Act gives creators control over how their work is used. Ethical issues include the digital divide, environmental impact from e-waste and data centres, and the effects of AI bias on society.
版权和知识产权法律保护创作者的权利。软件盗版、未经许可下载受版权保护的内容以及剽窃都是违法的。《版权、设计和专利法》赋予创作者对其作品使用方式的控制权。伦理问题包括数字鸿沟、电子垃圾和数据中心对环境的影响，以及人工智能偏见对社会的影响。
Open source and proprietary software represent different licensing models. Open source software makes its source code freely available, allowing users to study, modify and distribute it. Proprietary software is owned by a company and its source code is kept secret; users purchase a licence to use it. Each has advantages in terms of cost, support and customisation.
开源和专有软件代表不同的许可模式。开源软件将其源代码免费提供，允许用户学习、修改和分发。专有软件归公司所有，其源代码保密；用户购买许可证使用它。两者在成本、支持和定制方面各有优势。
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