📚 Data Storage | 数据存储
Data storage is the physical recording of information so that it can be kept, retrieved and used later. In science and technology, storage is essential for measurements, computer programs, documents, photographs, sound and video. Different storage media use magnetic, optical or electronic principles to represent data.
数据存储是将信息进行物理记录，使其能够被保存、读取和以后使用。在科学与技术中，存储对于测量数据、计算机程序、文档、照片、声音和视频都至关重要。不同的存储介质利用磁、光或电子原理来表示数据。
1. Why Data Needs to Be Stored | 为什么需要存储数据
Digital devices need storage to hold the operating system, application software and user files. Without storage, a computer would lose all information as soon as the power is switched off.
数字设备需要存储来保存操作系统、应用软件和用户文件。没有存储，计算机一旦断电就会丢失所有信息。
Scientists also use data storage to record experimental results, sensor readings and images over long periods. Reliable storage allows data to be analysed, shared and compared many times.
科学家也使用数据存储长期记录实验结果、传感器读数和图像。可靠的存储使数据能够被多次分析、共享和比较。
2. Bits, Bytes and Binary | 位、字节与二进制
All digital data is represented as binary digits, or bits. A single bit can have one of two values: 0 or 1. These values correspond to two physical states, such as two directions of magnetisation, two levels of reflected light, or two amounts of stored charge.
所有数字数据都用二进制数字（位）表示。一个位只能取两个值之一：0 或 1。这两个值对应两种物理状态，例如两个磁化方向、两个光反射水平或两个存储电荷量。
Eight bits are grouped into one byte. A byte can store 2⁸ = 256 different values, which is enough to represent one text character in many coding systems.
八个位组成一个字节。一个字节可以存储 2⁸ = 256 种不同的值，足以在许多编码系统中表示一个文本字符。
3. Units of Storage Capacity | 存储容量单位
Storage capacity is measured in bytes. Larger units are formed by multiplying by about 1000, although operating systems often use binary multiples based on 1024.
存储容量以字节为单位。更大的单位通过约乘以 1000 形成，不过操作系统常使用基于 1024 的二进制倍数。
| Unit | Symbol | Approximate size |
|---|---|---|
| bit | b | 1 binary digit |
| byte | B | 8 bits |
| kilobyte | KB | 10³ B or 1024 B |
| megabyte | MB | 10⁶ B |
| gigabyte | GB | 10⁹ B |
| terabyte | TB | 10¹² B |
For IGCSE calculations, 1 KB is often treated as 1024 bytes, while storage manufacturers usually advertise 1 KB as 1000 bytes. This is why a drive labelled 1 TB can appear smaller in an operating system.
在 IGCSE 计算中，1 KB 通常取 1024 字节，而存储制造商通常将 1 KB 标为 1000 字节。因此，标为 1 TB 的硬盘在操作系统中可能显示得更小。
4. Magnetic Storage: Hard Disk Drives | 磁存储：硬盘驱动器
A hard disk drive stores data by magnetising tiny regions on a spinning platter coated with magnetic material. A read/write head floats just above the platter surface to write and read data.
硬盘驱动器通过在涂有磁性材料的旋转盘片上磁化微小区域来存储数据。读写头悬浮在盘片表面上方进行数据的写入和读取。
The direction of magnetisation represents binary values: one direction stands for 1 and the opposite direction stands for 0. Data is organised into circular tracks and small arc sections called sectors.
磁化方向代表二进制值：一个方向代表 1，相反方向代表 0。数据被组织成圆形磁道和称为扇区的小弧形区域。
5. Optical Storage: CDs, DVDs and Blu-ray | 光存储：CD、DVD 和蓝光
Optical discs store data as tiny pits and flat areas called lands on a reflective surface. A laser beam is directed at the disc, and the difference in reflection between a pit and a land is detected by a photodiode.
光盘将数据存储为反射表面上的微小凹坑和称为平面的平坦区域。激光束照射到光盘上，凹坑与平面之间的反射差异由光电二极管检测。
A CD can hold about 700 MB, a single-layer DVD about 4.7 GB, and a single-layer Blu-ray disc about 25 GB. Blu-ray uses a blue laser with a shorter wavelength, so the pits can be smaller and packed more closely together.
一张 CD 约可存储 700 MB，单层 DVD 约 4.7 GB，单层蓝光光盘约 25 GB。蓝光使用波长更短的蓝色激光，因此凹坑可以更小、排列更密集。
6. Solid-State Storage: Flash Memory and SSDs | 固态存储：闪存和固态硬盘
Flash memory stores bits electronically using floating-gate transistors that can trap electric charge. The amount of stored charge changes the threshold voltage of the transistor, allowing 0 and 1 to be distinguished.
闪存使用能够捕获电荷的浮动栅极晶体管以电子方式存储位。存储电荷的多少会改变晶体管的阈值电压，从而区分 0 和 1。
Examples of solid-state storage include USB flash drives, SD cards and solid-state drives. Because there are no moving parts, flash memory is faster, quieter and more resistant to physical shock than magnetic disks.
固态存储的例子包括 U 盘、SD 卡和固态硬盘。由于没有移动部件，闪存比磁盘更快、更安静，也更耐物理冲击。
7. How Magnetic Storage Works | 磁存储的工作原理
During writing, an electric current passes through the read/write head and creates a magnetic field. This field magnetises a small region of the platter in one of two directions, representing a 0 or a 1.
写入时，电流通过读写头并产生磁场。该磁场将盘片上的一个小区域磁化为两个方向之一，表示 0 或 1。
During reading, the magnetised regions pass under the head and induce tiny voltage changes. These changes are converted back into binary data by the drive electronics.
读取时，磁化区域在读写头下方经过，感应出微小的电压变化。这些变化由硬盘电子电路转换回二进制数据。
The platter spins at high speed, typically 5400 or 7200 revolutions per minute. The head moves radially across the platter to access different tracks, which is why hard disk drives have mechanical access delay.
盘片高速旋转，通常为每分钟 5400 或 7200 转。读写头沿盘片径向移动以访问不同磁道，因此硬盘驱动器存在机械访问延迟。
8. How Optical Storage Works | 光存储的工作原理
An optical disc has a single spiral track starting near the centre and ending at the outer edge. The track contains microscopic pits and lands. When the laser hits a pit, less light reflects back than when it hits a land.
光盘有一条从中心附近开始、到外缘结束的螺旋轨道。轨道上有微小的凹坑和平面。当激光照射到凹坑时，反射回来的光比照射到平面时少。
Pits and lands do not directly represent 1 and 0. Instead, the transition from a pit to a land, or from a land to a pit, is used to encode bits. This encoding helps keep the length of pits within a practical range.
凹坑与平面并不直接代表 1 和 0。相反，凹坑到平面或平面到凹坑的跳变被用来编码位。这种编码有助于将凹坑长度保持在实用的范围内。
Optical media are useful for distributing music, films, software and archived files because they are cheap to manufacture in large quantities.
光介质适合分发音乐、电影、软件和存档文件，因为大规模生产成本低。
9. How Solid-State Storage Works | 固态存储的工作原理
In a flash memory cell, a control gate and a floating gate are separated by a thin oxide layer. To write data, a high voltage injects electrons through the oxide layer into the floating gate. The trapped electrons change the threshold voltage of the cell.
在闪存单元中，控制栅和浮动栅由一层薄氧化层隔开。写入数据时，高电压使电子穿过氧化层进入浮动栅。被捕获的电子改变了单元的阈值电压。
To read data, the controller applies a known voltage and measures whether the cell conducts. A charged floating gate blocks conduction, while an uncharged gate allows it, so the two states can represent 0 and 1.
读取数据时，控制器施加一个已知电压并测量单元是否导通。带电的浮动栅会阻止导通，而不带电的栅则允许导通，因此这两种状态可以表示 0 和 1。
NAND flash organises cells into a large grid. Multi-level cells can store more than one bit per cell by using several distinct charge levels, which increases storage density but reduces reliability compared with single-level cells.
NAND 闪存将单元组织成大型网格。多级单元通过使用多个不同的电荷级别，每个单元可存储多个位，从而提高了存储密度，但与单级单元相比可靠性有所降低。
10. Comparing Storage Media | 比较存储介质
| Property | Magnetic HDD | Optical disc | Solid-state flash |
|---|---|---|---|
| Moving parts | Yes, spinning platter | Yes, spinning disc | No |
| Typical capacity | Up to about 20 TB | CD 700 MB, DVD 4.7 GB, Blu-ray 25 GB per layer | 128 GB to 4 TB |
| Access speed | Moderate | Slow | Fast |
| Durability | Sensitive to shock | Sensitive to scratches | Shock resistant |
| Cost per GB | Low | Low | Higher |
Hard disk drives offer very large capacity at low cost, but they are slower and more fragile than solid-state drives. Optical discs are cheap and portable, but their capacity and speed are limited.
硬盘驱动器以低成本提供非常大的容量，但比固态硬盘更慢、更脆弱。光盘便宜且便于携带，但容量和速度有限。
Solid-state drives are the fastest and most robust, but they cost more per gigabyte. The best choice therefore depends on whether speed, capacity, portability or cost is most important.
固态硬盘最快、最耐用，但每 GB 成本更高。因此，最佳选择取决于速度、容量、便携性或成本哪一个最重要。
11. Analogue vs Digital Data | 模拟数据与数字数据
Analogue data varies continuously with time. For example, a microphone produces a voltage that changes smoothly according to the sound wave. Any small noise or distortion directly changes the analogue signal.
模拟数据随时间连续变化。例如，麦克风根据声波产生平滑变化的电压。任何微小噪声或失真都会直接改变模拟信号。
Digital data uses discrete binary values, usually 0 and 1. Once a measurement has been converted into binary form, copies can be made without adding noise, so digital signals are more reliable for storage and transmission.
数字数据使用离散的二进制值，通常为 0 和 1。一旦测量结果被转换成二进制形式，就可以在不增加噪声的情况下进行复制，因此数字信号在存储和传输中更可靠。
Modern data storage is almost entirely digital because binary states can be represented physically with high repeatability and accuracy.
现代数据存储几乎完全是数字化的，因为二进制状态可以被物理表示，且具有很高的可重复性和准确性。
12. Choosing Storage for Different Uses | 为不同用途选择存储方式
Operating systems and frequently used programs benefit from the speed of solid-state drives. Very large archive and backup copies are often kept on hard disk drives because their cost per gigabyte is low.
操作系统和常用程序受益于固态硬盘的速度。非常大的归档和备份副本通常保存在硬盘驱动器上，因为每 GB 成本较低。
Optical discs may be used to distribute films, music and software, or to keep a read-only copy of important data. USB flash drives are convenient for moving files between devices because they are small, fast and easy to carry.
光盘可用于分发电影、音乐和软件，或保存重要数据的只读副本。U 盘便于在设备之间移动文件，因为体积小、速度快且易于携带。
Cloud storage is remote storage accessed through a network. It allows data to be synchronised across devices, but it depends on an internet connection and the security of the service provider.
云存储是通过网络访问的远程存储。它允许数据在多个设备之间同步，但依赖互联网连接和服务提供商的安全性。
No single storage medium is best for every task. A sensible choice balances speed, capacity, durability, portability and cost against the needs of the user.
没有一种存储介质最适合所有任务。合理的选择应在速度、容量、耐用性、便携性和成本之间根据用户需求进行权衡。
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