GCSE AQA Computer Science: Last-Minute Revision Notes | GCSE AQA 计算机：考前冲刺笔记

📚 GCSE AQA Computer Science: Last-Minute Revision Notes | GCSE AQA 计算机：考前冲刺笔记

As the GCSE AQA Computer Science exams approach, efficient last-minute revision is key. These notes distil the entire specification into concise, bilingual sections to help you quickly recall essential concepts for both Paper 1 and Paper 2. Every core topic is broken down into bite-sized English–Chinese pairs so you can reinforce your understanding in the shortest possible time.

随着 GCSE AQA 计算机科学考试临近，高效的考前冲刺至关重要。这份笔记将全部考点浓缩为精简的双语小节，助你快速回顾 Paper 1 和 Paper 2 的关键概念。每一个核心主题都被拆解成英中对照的知识点，让你在最短时间内巩固理解。

1. Computational Thinking and Algorithms | 计算思维与算法

Computational thinking uses abstraction, decomposition, and algorithmic thinking to solve problems. Abstraction means removing unnecessary detail; decomposition breaks a complex problem into smaller, manageable parts.

计算思维运用抽象、分解和算法思维来解决问题。抽象意味着去除不必要的细节；分解则是将复杂问题拆分成更小、更可管理的部分。

An algorithm is a step-by-step sequence of instructions. It can be expressed using flowcharts or pseudocode. Efficiency matters: linear search checks each item one by one (O(n)), while binary search repeatedly halves a sorted list (O(log n)).

算法是逐步执行的指令序列，可用流程图或伪代码表达。效率很重要：线性查找逐个检查每一项（时间复杂度 O(n)），而二分查找对已排序列表不断对半划分（O(log n)）。

Sorting algorithms: bubble sort compares adjacent items and swaps them if they are in the wrong order; it is simple but slow for large lists. Merge sort divides the list into smaller sub-lists, sorts each, and then merges them—it is more efficient for large data sets.

排序算法：冒泡排序比较相邻项并在顺序错误时交换，简单但对大数据集较慢。合并排序将列表分割为较小子列表，分别排序后再归并，对大数据集效率更高。

2. Programming Fundamentals | 编程基础

Fundamental data types include integer, real (float), Boolean, character, and string. Variables can change their stored value during execution, whereas constants remain fixed.

基本数据类型包括整数、实数（浮点数）、布尔型、字符和字符串。变量在执行期间可以改变存储值，而常量则保持不变。

Sequence, selection, and iteration are the three building blocks of programs. Selection is implemented with IF, ELSE IF, and ELSE. Iteration uses FOR loops (count-controlled) or WHILE loops (condition-controlled).

顺序、选择和迭代是程序的三大构建块。选择通过 IF、ELSE IF 和 ELSE 实现。迭代使用 FOR 循环（计数控制）或 WHILE 循环（条件控制）。

Data structures: a one-dimensional array (list) holds multiple items of the same type; a two-dimensional array resembles a grid or table. Records group related fields of mixed types. Subroutines (functions and procedures) promote reusability – functions return a value, procedures do not.

数据结构：一维数组（列表）存放相同类型的多个项；二维数组形似网格或表格。记录将相关的混合类型字段组合在一起。子程序（函数和过程）促进代码重用 – 函数返回值，过程不返回值。

3. Data Representation | 数据表示

Computers store data in binary (base-2), using only 0 and 1. To convert denary to binary, repeatedly divide the number by 2 and read the remainders from bottom to top. Hexadecimal (base-16) uses the symbols 0–9 and A–F; it compactly represents 4-bit groups – for example, 1010₂ = A₁₆.

计算机以二进制（基数为 2）存储数据，仅使用 0 和 1。十进制转二进制：反复除以 2 取余，从下往上读。十六进制（基数为 16）使用符号 0–9 和 A–F；它紧凑地表示 4 位一组 – 例如 1010₂ = A₁₆。

Character sets: ASCII uses 7 bits to represent 128 characters (including English letters, digits, and control codes). Unicode extends this to thousands of characters, supporting multiple languages and emojis, but requires more bits per character.

字符集：ASCII 使用 7 位表示 128 个字符（包括英文字母、数字和控制码）。Unicode 扩展至数千字符，支持多语言和表情符号，但每个字符需要更多位。

Images are composed of pixels. The colour depth determines how many bits represent each pixel’s colour; higher colour depth gives more colours. File size in bits = width(pixels) × height(pixels) × colour depth(bits). Metadata stores additional information such as dimensions and date created.

图像由像素组成。色深决定每个像素的颜色用多少位表示；色深越高，颜色越丰富。文件大小（位）= 像素宽度 × 像素高度 × 色深（位）。元数据存储尺寸、创建日期等附加信息。

Sound is sampled at a fixed rate (e.g., 44.1 kHz). File size = sample rate × bit depth × duration in seconds × number of channels. Both sampling rate and bit depth affect quality. Compression can be lossy (some data permanently discarded, e.g., MP3, JPEG) or lossless (all original data can be restored, e.g., ZIP, PNG).

声音以固定采样率（如 44.1 kHz）进行采样。文件大小 = 采样率 × 位深 × 时长（秒）× 声道数。采样率和位深共同影响音质。压缩可分为有损（永久丢弃部分数据，如 MP3、JPEG）或无损（可完整恢复原始数据，如 ZIP、PNG）。

Image file size (bits) = width × height × colour depth | 图像文件大小 = 宽 × 高 × 色深

4. Computer Systems & Architecture | 计算机系统与体系结构

The von Neumann architecture forms the basis of

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