📚 OCR Computer Science Year 1 Revision | OCR计算机科学第一年复习
Welcome to your comprehensive Year 1 revision guide for OCR Computer Science. This article breaks down the core AS-Level topics, covering computer systems, data representation, programming fundamentals, algorithms, and the ethical dimensions of computing. Each section presents essential concepts in clear English and Chinese, helping you reinforce understanding and exam readiness.
欢迎阅读 OCR 计算机科学第一年综合复习指南。本文梳理了 AS 阶段的核心考点，涵盖计算机系统、数据表示、编程基础、算法和计算伦理等模块。每个小节都用清晰的中英对照讲解关键概念，帮助你巩固知识、从容备考。
1. System Architecture Fundamentals | 系统架构基础
The Central Processing Unit (CPU) executes instructions following the fetch–decode–execute cycle. Its main components include 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).
中央处理器（CPU）遵循取指—译码—执行周期并执行指令。其主要部件包括控制器（CU）、算术逻辑单元（ALU）以及程序计数器（PC）、存储器地址寄存器（MAR）和存储器数据寄存器（MDR）等寄存器。
Performance is influenced by clock speed, number of cores, and cache size. Pipelining can improve throughput by overlapping the stages of multiple instructions, while Von Neumann architecture stores both data and instructions in a single shared memory.
性能受时钟频率、核心数量和缓存大小影响。流水线技术通过重叠多条指令的不同阶段来提高吞吐量，而冯·诺依曼架构则将数据和指令存储在单一共享内存中。
2. Data Representation and Number Systems | 数据表示与数制
Computers use binary to represent all data. Unsigned integers can be stored directly in binary, while signed integers often use two’s complement. In two’s complement, the most significant bit indicates the sign, and negative numbers are formed by inverting bits and adding one.
计算机使用二进制表示所有数据。无符号整数可直接用二进制存储，而有符号整数常采用补码。在补码中，最高位表示符号，负数通过按位取反再加一形成。
Characters are encoded using standards such as ASCII (7-bit) and Unicode (16-bit or variable length). Images are represented as pixels with a colour depth, and sound is sampled at a given sampling rate and bit depth.
字符采用 ASCII（7 位）和 Unicode（16 位或可变长度）等标准编码。图像以像素及其颜色深度表示，声音则以特定的采样率和位深度进行采样。
Binary arithmetic includes addition, subtraction (via two’s complement), and logical shifts. Overflow occurs when the result exceeds the available bit width. Text is stored by mapping each character to a binary code.
二进制运算包括加法、减法（通过补码）和逻辑移位。当结果超出可用位宽时会发生溢出。文本通过将每个字符映射到二进制编码来存储。
3. Processor Internals and Machine Instructions | 处理器内部结构与机器指令
The fetch–decode–execute cycle begins with fetching the instruction pointed to by the PC into the MDR, then incrementing the PC. The CU decodes the operation and controls the ALU and data movement among registers.
取指—译码—执行周期从把 PC 指向的指令取入 MDR 并递增 PC 开始。CU 译码操作并控制 ALU 以及寄存器间的数据传送。
Assembly language uses mnemonics like LDR, ADD, and B. Each assembly instruction corresponds to a machine code opcode. Operand addressing modes include immediate, direct, and indirect.
汇编语言使用 LDR、ADD 和 B 等助记符。每条汇编指令对应一个机器码操作码。操作数寻址方式包括立即寻址、直接寻址和间接寻址。
Interrupts allow external devices or software to signal the CPU, pausing the current process to run an Interrupt Service Routine (ISR). After servicing the interrupt, the original state is restored.
中断允许外部设备或软件向 CPU 发信号，暂停当前进程并运行中断服务程序（ISR）。处理完中断后恢复原始状态。
4. Memory Types and Storage Technologies | 内存类型与存储技术
RAM is volatile working memory, typically Dynamic RAM (DRAM) requiring constant refresh, while Static RAM (SRAM) is faster but more expensive. ROM is non‑volatile and stores firmware like BIOS.
RAM 是易失性工作内存，典型如需要持续刷新的动态 RAM（DRAM），而静态 RAM（SRAM）速度更快但更昂贵。ROM 是非易失性的，存储 BIOS 等固件。
Secondary storage includes magnetic hard disks, solid‑state drives (SSD) using NAND flash, and optical discs. Key metrics are capacity, speed (access time), durability, and portability.
辅助存储包括机械硬盘、使用 NAND 闪存的固态硬盘（SSD）以及光盘。关键指标是容量、速度（访问时间）、耐用性和便携性。
Virtual memory uses a portion of secondary storage as an extension of RAM, managed by paging. A disk thrashing situation occurs when excessive paging degrades performance.
虚拟内存利用部分辅助存储作为 RAM 的扩展，通过分页机制管理。当过度分页导致性能严重下降时会发生磁盘颠簸现象。
5. Input/Output and Communication Buses | 输入输出与通信总线
I/O devices connect via buses: the data bus, address bus, and control bus. The address bus width determines the maximum addressable memory, while data bus width affects how much data can be transferred per cycle.
I/O 设备通过总线连接：数据总线、地址总线和控制总线。地址总线宽度决定了最大可寻址内存，数据总线宽度影响每个周期能传输的数据量。
Polling and interrupts are two methods of I/O control. In polling the CPU repeatedly checks a device’s status, whereas interrupts free the CPU until a device requires service. Direct Memory Access (DMA) allows a device to transfer data directly to memory without involving the CPU for every byte.
轮询和中断是两种 I/O 控制方式。轮询中 CPU 重复检查设备状态，而中断则使 CPU 无需一直检查直到设备需要服务。直接存储器访问（DMA）允许设备直接将数据传输到内存，而不需要 CPU 参与每个字节的传送。
6. Operating Systems and Utility Software | 操作系统与实用软件
The OS manages hardware resources, provides a user interface, handles file management, and enforces security. Key functions include memory management (paging, segmentation), process scheduling (round‑robin, priority), and input/output management.
操作系统管理硬件资源、提供用户界面、处理文件管理并强制执行安全策略。关键功能包括内存管理（分页、分段）、进程调度（时间片轮转、优先级）和输入输出管理。
Utility software performs maintenance tasks: disk defragmentation reorganises fragmented files for faster access, backup utilities create copies of data, and antivirus software detects and removes malware.
实用软件执行维护任务：磁盘碎片整理重新组织碎片化的文件以加快访问，备份工具创建数据副本，杀毒软件检测并清除恶意软件。
The kernel is the core of the OS, running in privileged mode, and a monolithic kernel integrates all services while a microkernel keeps only essential functions in kernel space and runs services in user space.
内核是操作系统的核心，在特权模式下运行；宏内核集成所有服务，而微内核只在内核空间保留最基本功能，将服务运行在用户空间。
7. Programming Fundamentals and Paradigms | 编程基础与范式
Variables store data of a specific type (integer, float, Boolean, char, string). Constants hold values that cannot change at runtime. Assignment, arithmetic, relational, and logical operators form the basis of expressions.
变量存储特定类型的数据（整型、浮点型、布尔型、字符、字符串）。常量保存运行时不可更改的值。赋值、算术、关系和逻辑运算符构成了表达式的基础。
Control structures include sequence, selection (IF, CASE), and iteration (FOR, WHILE, REPEAT). These structures determine the flow of execution and are common across imperative programming languages.
控制结构包括顺序、选择（IF、CASE）和迭代（FOR、WHILE、REPEAT）。这些结构决定执行流程，在各种命令式编程语言中普遍存在。
Procedural programming uses procedures and functions to modularise code, promoting reuse and maintainability. A function returns a single value, while a procedure may perform actions without returning a value.
过程式编程使用过程和函数来模块化代码，以促进重用和维护。函数返回一个值，而过程可能执行操作而不返回值。
8. Data Structures and Algorithm Design | 数据结构与算法设计
Arrays store elements of the same type in contiguous memory locations accessed by index. A 2D array can be visualised as a table of rows and columns. Records group related fields of potentially different types into a single entity.
数组将相同类型的元素存储在连续的内存位置中，并通过索引访问。二维数组可看作行和列的表格。记录将可能不同类型的相关字段组合成一个实体。
Searching algorithms: linear search checks each element sequentially (O(n)); binary search requires a sorted list and repeatedly halves the search space (O(log n)). Sorting algorithms include bubble sort, insertion sort, and merge sort.
查找算法：线性查找依次检查每个元素（O(n)）；二分查找要求列表有序并反复对半查找空间（O(log n)）。排序算法包括冒泡排序、插入排序和归并排序。
Stacks and queues are abstract data types. A stack is LIFO (last‑in first‑out) with operations push and pop; a queue is FIFO (first‑in first‑out) with enqueue and dequeue. They are used in expression evaluation, backtracking, and print spooling.
栈和队列是抽象数据类型。栈是后进先出（LIFO），有压入和弹出操作；队列是先进先出（FIFO），有入队和出队操作。它们用于表达式求值、回溯和打印缓冲。
9. Networks, Protocols and the Internet | 网络、协议与互联网
A network can be LAN (Local Area Network) or WAN (Wide Area Network). Common topologies include star, bus, and mesh. In a client‑server model, central servers provide services to clients; in peer‑to‑peer all devices share resources equally.
网络可以是局域网（LAN）或广域网（WAN）。常见拓扑有星型、总线型和网状型。在客户端‑服务器模型中，中央服务器为客户端提供服务；在点对点网络中所有设备平等共享资源。
The TCP/IP stack consists of four layers: Application (HTTP, FTP, SMTP), Transport (TCP, UDP), Internet (IP), and Network Access (Ethernet, Wi‑Fi). TCP provides reliable, ordered delivery with error checking, while UDP is connectionless and faster.
TCP/IP 协议栈包含四层：应用层（HTTP、FTP、SMTP）、传输层（TCP、UDP）、互联网层（IP）和网络接入层（以太网、Wi‑Fi）。TCP 提供带错误检查的可靠有序传送，而 UDP 无连接且速度更快。
Packet switching breaks data into packets routed independently across the network. Each packet contains source and destination IP addresses and a sequence number for reassembly. Routers forward packets based on routing tables.
包交换将数据分割成包，各自独立在网络中路由。每个包包含源 IP 地址、目的 IP 地址以及用于重组的序号。路由器根据路由表转发包。
10. Databases, SQL and Entity Relationships | 数据库、SQL 与实体关系
A relational database organises data into tables (relations) linked by primary and foreign keys. Each table has a primary key that uniquely identifies each record. Foreign keys enforce referential integrity between tables.
关系数据库将数据组织为由主键和外键关联的表（关系）。每个表有一个唯一标识每条记录的主键。外键强制表之间的引用完整性。
Structured Query Language (SQL) is used to define and manipulate data. Key commands include SELECT … FROM … WHERE, INSERT INTO, UPDATE … SET … WHERE, and DELETE FROM. A typical query:
结构化查询语言（SQL）用于定义和操作数据。核心命令包括 SELECT … FROM … WHERE、INSERT INTO、UPDATE … SET … WHERE 和 DELETE FROM。典型查询：
SELECT StudentName FROM Students WHERE YearGroup = 12;
Entity‑relationship diagrams model data by showing entities (tables), attributes, and relationships (one‑to‑one, one‑to‑many, many‑to‑many). Normalisation reduces redundancy, typically reaching Third Normal Form (3NF) to eliminate transitive dependencies.
实体关系图通过显示实体（表）、属性和关系（一对一、一对多、多对多）来建模数据。规范化减少冗余，通常达到第三范式（3NF）以消除传递依赖。
11. Legal, Ethical and Environmental Issues | 法律、伦理与环境问题
The Data Protection Act (DPA 2018) regulates the collection and processing of personal data, with principles such as data minimisation, accuracy, and storage limitation. The Computer Misuse Act criminalises unauthorised access, hacking, and malware creation.
《数据保护法》（2018）规范个人数据的收集和处理，遵循数据最小化、准确性和存储限制等原则。《计算机滥用法》将未经授权的访问、黑客攻击和恶意软件制作定为刑事犯罪。
Ethical concerns include the digital divide, online censorship, and artificial intelligence bias. Environmental impacts arise from e‑waste, energy consumption of data centres, and the carbon footprint of device manufacturing.
伦理问题包括数字鸿沟、网络审查和人工智能偏见。环境影响来自电子垃圾、数据中心的能耗以及设备制造的碳足迹。
The Creative Commons licensing model enables creators to grant usage rights while retaining copyright. Open‑source software promotes transparency and collaborative development, contrasting with proprietary software.
知识共享许可模式让创作者在保留版权的同时授予使用权。开源软件促进透明度和协作开发，与专有软件形成对比。
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