📚 IB Computer Science: High-Frequency Topics Summary | IB 计算机：高频考点总结
Preparing for the IB Computer Science examinations requires a clear understanding of the most frequently assessed topics across the core syllabus and HL extensions. This article distills key concepts, typical question areas, and essential terminology that regularly appear in Papers 1, 2 and the case study. Mastering these high-yield topics will help you solve problems efficiently and write precise answers.
备考IB计算机科学考试，需要清晰掌握核心大纲和HL扩展部分中最常考查的主题。本文提炼了常出现在Paper 1、Paper 2和案例研究中的关键概念、典型考点及必备术语。吃透这些高频主题，能帮助你高效解题并写出精准的答案。
1. Computer Architecture and the Fetch-Decode-Execute Cycle | 计算机体系结构与取指-译码-执行周期
The CPU operates on the stored program concept, where both instructions and data reside in the same memory. The fetch-decode-execute cycle describes how the control unit retrieves an instruction pointed to by the program counter (PC), decodes it in the instruction register (IR), and then executes it using the ALU or other components.
CPU基于存储程序概念工作，指令和数据存放在同一个内存中。取指-译码-执行周期描述了控制单元如何根据程序计数器（PC）取出指令，在指令寄存器（IR）中译码，然后利用ALU或其他部件执行。
Key registers include the memory address register (MAR) and the memory data register (MDR). The clock speed sets the pace, while multi-core processors enable parallel execution. Questions often ask you to trace the cycle or identify which register holds which value at each step.
重要的寄存器有内存地址寄存器（MAR）和内存数据寄存器（MDR）。时钟频率决定了节拍，而多核处理器支持并行执行。考题经常要求你跟踪周期的每一步，或指出各步骤中哪个寄存器保存了什么值。
2. Secondary Storage and Virtual Memory | 辅助存储与虚拟内存
Secondary storage devices vary in speed, cost and durability. Magnetic hard drives use spinning platters, while solid-state drives (SSD) rely on flash memory with no moving parts. Optical media like Blu-ray use laser technology. IB questions love comparing access times and suitability for different scenarios.
辅助存储设备在速度、成本和耐用性上各不相同。机械硬盘使用旋转盘片，固态硬盘（SSD）则依赖没有活动部件的闪存。蓝光等光学介质采用激光技术。IB考题喜欢比较不同设备的访问时间及其适用场景。
Virtual memory extends RAM by using a section of the hard drive. When physical memory is full, the operating system swaps pages between RAM and secondary storage. This causes disk thrashing if overused, and you are expected to explain the role of the memory management unit (MMU).
虚拟内存通过使用硬盘的一部分来扩展RAM。当物理内存不足时，操作系统在RAM和辅助存储器之间交换页面。过度使用会引起磁盘抖动，考试中你需要解释内存管理单元（MMU）的作用。
3. Data Representation: Binary, Hexadecimal and Floating Point | 数据表示：二进制、十六进制与浮点数
All data inside a computer is represented in binary. Converting between binary, denary and hexadecimal is a core skill. A nibble (4 bits) maps exactly to one hex digit. IB papers frequently test this conversion, especially in tracing memory dumps or color codes.
计算机内部所有数据都以二进制表示。在二进制、十进制和十六进制之间转换是核心技能。一个半字节（4位）恰好对应一个十六进制数字。IB试卷经常考查这种转换，尤其用于追踪内存转储或颜色代码。
Negative integers can be stored using sign-and-magnitude or, far more commonly, two’s complement. The formula for the range of n-bit two’s complement is shown below. Floating-point numbers use a mantissa and an exponent, often in IEEE 754 style. You must be able to normalize a binary floating-point number and calculate the smallest/largest values possible.
负整数可以用符号-幅值法或更常见的是补码表示。n位补码的范围如下公式所示。浮点数使用尾数和指数，通常按照IEEE 754格式。你必须能够对二进制浮点数进行规格化，并计算可能的最小/最大值。
n-bit two’s complement range: -2n-1 to 2n-1 – 1
Floating-point representation is often written as ± mantissa × 2exponent. Normalisation maximises precision by eliminating leading zeros in the mantissa. The IB exam may ask you to represent a decimal fraction in binary scientific notation or to detect overflow and underflow.
浮点数表示通常写作 ± 尾数 × 2指数。规格化通过消除尾数中的前导零来最大化精度。IB考试可能会要求你将十进制小数表示为二进制科学记数法，或检测上溢和下溢。
4. Operating Systems and Resource Management | 操作系统与资源管理
The operating system (OS) manages hardware resources through process scheduling, memory management, file management and I/O handling. IB frequently asks about the difference between preemptive and non-preemptive scheduling, or how a round-robin scheduler works.
操作系统通过进程调度、内存管理、文件管理和输入/输出处理来管理硬件资源。IB经常考查抢占式与非抢占式调度的区别，或者轮转调度器如何工作。
Interrupts alter the normal flow of program execution. When an interrupt occurs, the current state is saved, the ISR (interrupt service routine) is executed, and control is returned. Recognizing the difference between hardware and software interrupts is a typical short-answer focus.
中断会改变程序正常执行流程。当中断发生时，当前状态被保存，中断服务程序（ISR）被执行，然后交还控制权。辨别硬件中断与软件中断的区别是典型的简答题考点。
Paging and segmentation are memory management techniques. The OS splits memory into fixed-size pages, mapping virtual addresses to physical frames. A page fault occurs when the required page is not in RAM, triggering a fetch from disk. Questions on virtual memory demand clear explanation of this process.
分页和分段是内存管理技术。操作系统将内存分为固定大小的页面，将虚拟地址映射到物理帧。当所需页面不在RAM中时会发生缺页异常，触发从磁盘读取。有关虚拟内存的题目需要清晰解释这一过程。
5. Network Fundamentals and Topologies | 网络基础与拓扑结构
LANs, WLANs and WANs differ in geographical scope and the technologies used. IB expects you to describe the role of MAC addresses in a local network and to identify characteristics of topologies such as star, bus and mesh, including their advantages and drawbacks.
局域网、无线局域网和广域网在地理范围和使用技术上各不相同。IB要求你描述MAC地址在局域网中的作用，并能指出星型、总线型和网状等拓扑的特点，包括其优缺点。
6. The Internet and Protocol Suites | 互联网与协议套件
The TCP/IP model (or the OSI model) forms the backbone of internet communication. You must be able to explain the function of IP addressing (IPv4 vs IPv6), the role of routers in packet switching, and how DNS resolves domain names to IP addresses. Subnetting questions occasionally appear.
TCP/IP模型（或OSI模型）构成了互联网通信的支柱。你必须能够解释IP寻址的作用（IPv4与IPv6）、路由器在分组交换中的角色，以及DNS如何将域名解析为IP地址。偶尔也会出现子网划分的题目。
Protocols such as HTTP, HTTPS, FTP, SMTP and POP3/IMAP each serve a specific application. You need to know the purpose of each, the port numbers if required, and the difference between stateless (HTTP) and stateful (FTP) protocols. Security protocols like SSL/TLS for encryption are also tested.
HTTP、HTTPS、FTP、SMTP和POP3/IMAP等协议各司其职。你需要了解每个协议的目的、必要的端口号，以及无状态（HTTP）和有状态（FTP）协议的区别。像SSL/TLS这样的安全协议也是考点。
7. Algorithm Design and Efficiency Analysis | 算法设计与效率分析
Algorithmic thinking involves breaking down a problem into logical steps. IB Paper 2 and the HL case study expect you to write, trace and modify pseudocode. Recursion, a powerful HL topic, requires a clear base case and recursive step to prevent infinite calls.
算法思维意味着将问题分解为逻辑步骤。IB的Paper 2和HL案例研究要求你编写、追踪和修改伪代码。递归是一个强有力的HL主题，需要明确的基准情形和递归步骤以避免无限调用。
Big O notation measures worst-case time or space complexity. Common complexities are O(1), O(log n), O(n), O(n log n) and O(n²). You must be able to analyse loops and nested loops, and compare algorithms such as linear search (O(n)) and binary search (O(log n)).
大O符号衡量最坏情况下的时间或空间复杂度。常见的复杂度有O(1)、O(log n)、O(n)、O(n log n)和O(n²)。你必须能够分析循环和嵌套循环，并比较线性搜索（O(n)）和二分搜索（O(log n)）等算法。
Sorting algorithms like bubble sort, selection sort and insertion sort are slow at O(n²) but straightforward. Merge sort and quicksort achieve O(n log n). IB questions often ask you to trace these algorithms on a given array or to identify the number of comparisons.
冒泡排序、选择排序和插入排序等排序算法速度较慢，为O(n²)，但简单易懂。归并排序和快速排序能达到O(n log n)。IB题目经常要求你在给定数组上追踪这些算法，或识别比较次数。
8. Abstract Data Structures | 抽象数据结构
A stack follows Last In First Out (LIFO) with operations push() and pop(). It is used in backtracking and expression evaluation. A queue is First In First Out (FIFO), essential for scheduling tasks. Linked lists allow dynamic memory allocation and efficient insertions/deletions.
栈遵循后进先出（LIFO）原则，具有push()和pop()操作，用于回溯和表达式求值。队列是先进先出（FIFO），对任务调度至关重要。链表支持动态内存分配和高效插入/删除。
Binary trees are hierarchical structures where each node has at most two children. Traversal methods – pre-order, in-order, post-order – produce different sequences. IB diagrams often require you to write the output of a traversal or construct a tree from given traversals.
二叉树是层次结构，其中每个节点最多有两个子节点。遍历方法——前序、中序、后序——产生不同序列。IB的图表题经常要求你写出某遍历的输出，或根据给定遍历序列构建树。
9. Programming Fundamentals and Subprograms | 编程基础与子程序
Basic programming constructs include variables, constants, data types (integer, string, boolean, float), conditionals (if…else), and loops (for, while). IB pseudocode follows a strict syntax; you need to be precise with indentation and keywords like “end if”, “end loop”.
基本编程构造包括变量、常量、数据类型（整型、字符串、布尔型、浮点型）、条件语句（if…else）和循环（for, while）。IB伪代码遵循严格的语法；你需要精确使用缩进和”end if”、”end loop”等关键字。
Subprograms, such as procedures and functions, promote modularity. Parameter passing can be by value (a copy is made) or by reference (the original variable can change). Distinguishing these is a frequent HL question, especially when tracing code that modifies arguments.
过程与函数等子程序提高了模块化程度。参数传递可以按值（传递副本）或按引用（可修改原变量）。区分二者是常见的HL考题，尤其是在追踪修改实参的代码时。
10. Object-Oriented Programming (OOP) | 面向对象编程
OOP organises code around classes and objects. A class defines attributes (data) and methods (behaviour). IB emphasises encapsulation, which hides internal state and provides public methods for interaction. Inheritance allows a subclass to reuse and extend the properties of a superclass.
面向对象编程围绕类和对象组织代码。类定义了属性（数据）和方法（行为）。IB强调封装性，它将内部状态隐藏起来，并提供公有方法进行交互。继承允许子类重用和扩展超类的属性。
Polymorphism enables a single interface to be used for different underlying forms. In exams, you may need to interpret a UML class diagram showing associations, multiplicities, and inheritance arrows. Writing simple class definitions in pseudocode is also common.
多态性使得一个接口可以用于不同的底层形态。考试中，你可能需要解读展示关联、多重性和继承箭头的UML类图。用伪代码编写简单的类定义也很常见。
11. Databases and Normalisation | 数据库与规范化
Relational databases store data in tables with rows (records) and columns (fields). Primary keys uniquely identify records, while foreign keys create relationships between tables. SQL queries using SELECT, FROM, WHERE, JOIN, and aggregate functions are frequently assessed.
关系数据库将数据存储在具有行（记录）和列（字段）的表中。主键唯一标识记录，外键在表之间建立关系。使用SELECT、FROM、WHERE、JOIN和聚合函数的SQL查询是常见考点。
Normalisation reduces data redundancy. The first normal form (1NF) requires atomic values and a primary key. 2NF removes partial dependencies on a composite key, and 3NF eliminates transitive dependencies. IB exam questions may ask you to normalise a given unnormalised table to 3NF step by step.
规范化旨在减少数据冗余。第一范式（1NF）要求原子值和主键。2NF消除对组合键的部分依赖，3NF消除传递依赖。IB考试题可能要求你逐步将一个未规范化的表规范化到3NF。
12. System Development Life Cycle, Security and Ethics | 系统开发生命周期、安全与伦理
The SDLC includes phases: analysis, design (including prototyping), implementation, testing, deployment and maintenance. IB distinguishes between waterfall and agile methodologies; you should be able to discuss the advantages of iterative development and user involvement.
系统开发生命周期包括分析、设计（含原型设计）、实施、测试、部署和维护等阶段。IB区分了瀑布模型和敏捷方法；你应该能够讨论迭代开发和用户参与的优势。
Security threats like malware, phishing, denial-of-service attacks and SQL injection must be understood alongside countermeasures such as firewalls, encryption and user training. Symmetric and asymmetric encryption, including the use of public/private keys, often appear in HL scenarios.
需要理解恶意软件、网络钓鱼、拒绝服务攻击和SQL注入等安全威胁，以及防火墙、加密和用户培训等对策。对称加密和非对称加密（包括公钥/私钥的使用）经常出现在HL场景题中。
Ethics and social implications are examined in Paper 1. Topics include data privacy, intellectual property, the digital divide and the environmental impact of computing. Answers must show balanced arguments referencing laws like GDPR and real-world examples.
伦理和社会影响在Paper 1中占有一席之地。主题包括数据隐私、知识产权、数字鸿沟以及计算对环境的影响。答案必须展示兼顾正反两面的论述，并引用GDPR等法规和现实案例。
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