Paper 1 · Computer Systems 试卷一 · 计算机系统

3.3 · Data storage

3.3 · 数据存储

Where data lives

数据存放在哪里

Primary storage the CPU reaches directly, secondary storage for keeping things, the three technologies behind it, and the trick that lets a computer act as though it has more memory than it does.

CPU 可直接访问的主存储、用于长期保存数据的辅助存储、支撑它们的三种技术,以及让计算机表现得仿佛拥有比实际更多内存的技巧。

Core for all candidates 所有考生均需掌握的核心内容 Covers 3.3.1 to 3.3.6 涵盖 3.3.1 至 3.3.6 Features of each type are marked 每种类型的特征都会被评分

Explainer · 3.3.1

讲解 · 3.3.1

Primary storage

主存储

Primary storage is the memory the CPU can access directly. It holds RAM and ROM.

主存储是 CPU 能够直接访问的内存,包括 RAM 和 ROM。

RAM (random access memory)RAM(随机存取存储器) ROM (read only memory)ROM(只读存储器)
Volatile?是否易失? Volatile: contents are lost when the power goes off易失性:断电后内容会丢失 Non-volatile: contents stay when the power goes off非易失性:断电后内容仍会保留
Can it be changed?能否被改写? can be read from and written to可读可写 can only be read; contents are fixed只能读取;内容固定不变
What it holds存放的内容 the programs, the data and the parts of the operating system that are running right now当前正在运行的程序、数据以及操作系统的相关部分 the start-up instructions (the bootstrap / BIOS) the computer needs the moment it is switched on计算机开机瞬间所需的启动指令(引导程序 / BIOS)
!

A computer needs both. Without ROM there are no instructions to start up with (RAM is empty at power-on). Without RAM there is nowhere to hold the running programs and data. The one-line difference: RAM is volatile and can be changed; ROM is non-volatile and cannot.

计算机两者都需要。没有 ROM,就没有开机所需的指令(开机时 RAM 是空的)。没有 RAM,就无处存放正在运行的程序和数据。一句话概括两者的区别:RAM 是易失性的且可被改写;ROM 是非易失性的且不能被改写。

Explainer · 3.3.2

讲解 · 3.3.2

Secondary storage

辅助存储

Secondary storage is not accessed directly by the CPU. It is non-volatile, so it keeps data for as long as the user wants, and it holds far more than primary storage. Everything not currently in use lives here: the operating system, all installed applications, and the user’s files.

辅助存储是 CPU 不能直接访问的存储。它是非易失性的,因此可以按用户意愿长期保存数据,且容量远大于主存储。所有当前未在使用的内容都存放在这里:操作系统、所有已安装的应用程序,以及用户的文件。

!

The defining point is “not directly accessed by the CPU”, and that it is non-volatile. “It is slower” and “it is bigger” are true but are not the definition. An SSD is secondary storage even though it is fast.

定义的关键在于"CPU 不能直接访问",以及它是非易失性的。"速度较慢"和"容量较大"虽然属实,但并非定义本身。SSD 尽管速度很快,依然属于辅助存储。

Try it yourself

动手试试

Where does it live

它存放在哪里

Tag each item as being held in RAM, in ROM, or in secondary storage, then check.

将每一项标记为存放在 RAM、ROM 还是辅助存储中,然后进行检查。

Explainer · 3.3.3

讲解 · 3.3.3

Magnetic, optical and solid-state storage

磁性、光学与固态存储

Type类型 How it works工作原理 Examples示例
Magnetic磁性存储 spinning platters divided into tracks and sectors; electromagnets in the read-write heads read and write the data by magnetising areas of the surface. Has moving parts 旋转的盘片被划分为磁道和扇区;读写磁头中的电磁铁通过磁化盘片表面区域来读写数据。含有活动部件 hard disk drive (HDD)硬盘驱动器(HDD)
Optical光学存储 a laser burns pits and lands along a spiral track to write, and reads them back by how they reflect the laser 激光沿螺旋轨道刻录出凹坑与平面来写入数据,并通过它们对激光的不同反射方式来读取数据 CD, DVD, Blu-rayCD、DVD、蓝光光盘
Solid-state (flash)固态存储(闪存) NAND or NOR chips with millions of transistors in pairs, a control gate and a floating gate. Data is stored by trapping electrons in the floating gate. No moving parts NAND 或 NOR 芯片,包含数百万对晶体管,各带一个控制栅和一个浮动栅。数据通过将电子困于浮动栅中来存储。没有活动部件 solid-state drive (SSD), SD card, USB drive固态硬盘(SSD)、SD 卡、USB 闪存盘
!

Markers report students cannot state the features of each type. Learn the key words: magnetic = platters, tracks and sectors, electromagnets, moving parts; optical = laser, pits and lands; solid-state = transistors, control gate and floating gate, electrons, no moving parts. If asked how data is written to optical media, describe the laser burning the pits, not reading them.

考官报告显示,考生无法说出每种类型的特征。记住关键词:磁性存储 = 盘片、磁道与扇区、电磁铁、活动部件;光学存储 = 激光、凹坑与平面;固态存储 = 晶体管、控制栅与浮动栅、电子、无活动部件。若被问及数据如何写入光学介质,应描述激光刻录凹坑的过程,而不是读取过程。

Try it yourself

动手试试

Compare storage types

比较存储类型

Click a type to see its features and where it fits.

点击某个类型,查看其特征及适用场景。

Explainer · 3.3.4

讲解 · 3.3.4

Virtual memory

虚拟内存

When the programs running need more memory than the RAM holds, the computer would crash. Virtual memory prevents this. A part of secondary storage (the HDD or SSD) is set aside as swap space. Data is handled in fixed-size blocks called pages.

当正在运行的程序所需内存超过 RAM 容量时,计算机本会崩溃。虚拟内存可以防止这种情况发生。辅助存储(HDD 或 SSD)的一部分会被划出作为交换空间。数据以固定大小的块进行处理,这些块称为页。

Step步骤What happens发生了什么
1a program needs a page that is not in RAM, but RAM is full某个程序需要一个不在 RAM 中的页,但 RAM 已满
2the least recently used page in RAM is copied out to the swap space on secondary storageRAM 中最近最少使用的页被复制到辅助存储上的交换空间
3that RAM slot is now free; the page the program needs is loaded into it该 RAM 位置现已空出;程序所需的页被载入其中
4if a page that was swapped out is needed again later, another page is swapped out and it is brought back in若之后又需要用到已换出的页,则会再换出另一个页,并把它换回来
!

Markers report this is answered badly. Do not just say “extra memory”. The marked points are: secondary storage is partitioned to create the swap space, and pages of data are moved between RAM and that swap space as needed. Accessing a page in virtual memory is slower than in RAM, which is why more RAM makes a computer faster.

考官报告显示这一点回答得很差。不要只写"额外的内存"。得分要点是:辅助存储被划分出一部分用作交换空间,以及数据页会根据需要在 RAM 与该交换空间之间移动。在虚拟内存中访问一个页比在 RAM 中慢,这也是为什么更多的 RAM 能让计算机运行更快。

Try it yourself

动手试试

Paging in action

分页过程演示

RAM has four slots, all full. Step through as the computer makes room for a new page and later brings an old one back.

RAM 有四个位置,已全部占满。一步步观看计算机如何为新页腾出空间,并在之后把旧页换回来。

RAM (4 slots)

RAM(4 个位置)

Swap space (on the SSD)

交换空间(位于 SSD 上)

Explainer · 3.3.5 and 3.3.6

讲解 · 3.3.5 与 3.3.6

Cloud storage

云存储

Cloud storage keeps your data on remote servers run by a hosting company, reached over the internet, instead of on a local device. The provider needs physical servers and storage in data centres to hold it, often with copies on more than one server.

云存储将你的数据保存在由托管公司运营的远程服务器上,通过互联网访问,而不是保存在本地设备上。提供商需要在数据中心部署物理服务器与存储设备来保存数据,通常还会在多台服务器上保留副本。

Advantages of cloud vs local云存储相较本地存储的优点 Disadvantages of cloud vs local云存储相较本地存储的缺点
reach your files from any device, anywhere with internet只要有网络,任何设备、任何地点都能访问你的文件 you cannot get to your files without an internet connection; a slow connection makes it painful没有网络连接就无法访问文件;网速慢时体验很差
no need to carry a storage device, or use the same computer无需随身携带存储设备,也不必使用同一台电脑 ongoing subscription cost; large capacity or high transfer limits cost more需要持续支付订阅费用;更大的容量或更高的传输限额需要更多花费
the provider keeps back-ups, so a local drive failure does not lose the data提供商会保留备份,因此本地硬盘故障不会导致数据丢失 you depend on the provider: if the company fails or has an outage, you may lose access你依赖于提供商:若该公司倒闭或发生故障,你可能会失去访问权限
effectively unlimited capacity you can pay to expand容量几乎不受限制,可付费扩容 you hand control of your data’s security to the provider你将数据安全的控制权交给了提供商
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“The files could be hacked” is not a valid disadvantage of cloud storage: local files can be hacked too, so it is not a difference. A real disadvantage names something that is worse with cloud than with local, such as needing an internet connection.

"文件可能被黑客攻击"不是云存储的有效缺点:本地文件同样可能被黑客攻击,因此这并非两者的区别。真正的缺点应指出云存储比本地存储更差的地方,例如需要网络连接。

Try it yourself

动手试试

Cloud vs local

云存储与本地存储

Tag each statement as an advantage or a disadvantage of using cloud storage instead of local storage.

将每条陈述标记为使用云存储而非本地存储的优点或缺点。

Check your understanding

检验你的理解

Which memory holds the start-up instructions and keeps them when the power is off?

哪种内存保存启动指令,并且断电后仍能保留?

Check your understanding

检验你的理解

Is a solid-state drive (SSD) primary or secondary storage?

固态硬盘(SSD)属于主存储还是辅助存储?

Check your understanding

检验你的理解

What does virtual memory do when RAM is full?

当 RAM 已满时,虚拟内存会做什么?

Common mistakes

常见错误

Markers reported these patterns for 3.3.1 to 3.3.6 考官针对 3.3.1 至 3.3.6 报告了以下模式

RecurringCandidates cannot state the features of magnetic and solid-state storage. Magnetic: platters, tracks and sectors, electromagnets, moving parts. Solid-state: transistors, control gate and floating gate, movement of electrons, no moving parts.

反复出现考生无法说出磁性存储与固态存储的特征。磁性存储:盘片、磁道与扇区、电磁铁、活动部件。固态存储:晶体管、控制栅与浮动栅、电子移动、无活动部件。

Virtual memory is answered as “extra memory” with no mechanism. The marked points are that secondary storage is partitioned for swap space, and that pages of data move between RAM and that swap space when needed.

虚拟内存常被答成"额外的内存",却没有说明其机制。得分要点是辅助存储被划分出交换空间,以及数据页会在需要时于 RAM 与该交换空间之间移动。

Asked how data is written to an optical disc, candidates describe reading it instead. Writing is the laser burning pits into the track.

当被问及数据如何写入光盘时,考生却描述了读取过程。写入是激光在轨道上刻录凹坑的过程。

For a disadvantage of cloud storage, candidates say “the files could be hacked”. Local files can be hacked too, so it is not a disadvantage of cloud. A valid answer names something worse with cloud: needing an internet connection, ongoing cost, or depending on the provider.

对于云存储的缺点,考生常写"文件可能被黑客攻击"。本地文件同样可能被黑客攻击,因此这并非云存储特有的缺点。有效答案应指出云存储更差的地方:需要网络连接、持续产生费用,或依赖提供商。

✕

No mechanism: “Virtual memory is extra memory the computer uses when the RAM is full.”

没有说明机制:"虚拟内存是计算机在 RAM 已满时使用的额外内存。"

✓

The process: “Part of the SSD is used as swap space. When RAM is full, the least-used page is copied to the swap space, freeing a RAM slot for the page that is needed.”

说明了过程:"SSD 的一部分被用作交换空间。当 RAM 已满时,最少使用的页会被复制到交换空间,从而腾出一个 RAM 位置给所需的页。"

✕

Not a difference: “A disadvantage of cloud storage is that hackers could steal your files.”

并非真正的区别:"云存储的一个缺点是黑客可能窃取你的文件。"

✓

Worse with cloud: “A disadvantage is that you cannot reach your files at all without an internet connection.”

云存储确实更差的地方:"一个缺点是,没有网络连接就完全无法访问你的文件。"

Revision questions

复习题

Past-paper style. Write an answer, then reveal the marking points and mark yourself.

采用历年真题风格。写下答案,然后展开评分要点给自己打分。

Question 1 · 3 marks 第 1 题 · 3 分

[3]Give one difference between RAM and ROM, and explain why a computer needs both.

[3]说出 RAM 与 ROM 之间的一项区别,并解释为什么计算机两者都需要。

Question 2 · 4 marks 第 2 题 · 4 分

[4]Describe two features of solid-state storage and two features of magnetic storage.

[4]描述固态存储的两个特征以及磁性存储的两个特征。

Question 3 · 5 marks 第 3 题 · 5 分

[5]Explain how virtual memory is created and used when the RAM of a computer becomes full.

[5]解释当计算机的 RAM 已满时,虚拟内存是如何创建和使用的。

Question 4 · 4 marks 第 4 题 · 4 分

[4]Give two advantages and two disadvantages of storing photos in cloud storage rather than on a local hard drive.

[4]说出将照片存储在云端而不是本地硬盘上的两项优点和两项缺点。

Question 5 · 2 marks 第 5 题 · 2 分

[2]State whether a Blu-ray disc uses magnetic, optical or solid-state technology, and describe how data is written to it.

[2]说明蓝光光盘使用的是磁性、光学还是固态技术,并描述数据是如何写入其中的。

Flashcards

记忆卡片

Active recall for this subtopic’s key terms.

针对本子主题关键术语的主动回忆练习。

Prototype render · content grounded in the Cambridge IGCSE 0478 syllabus and real 0478 examiner-report data for 3.3 · not yet wired to live routes