Computer Storage
Unit 7 Summary - part 3
Hard Drive vs. RAM
Magnetic vs. Solid State
How Does Magnetic (Hard Disk Drive) Work?
HDDs are magnetic storage.
The unused blocks can be magnetized to be reused again to store data.
Optical Drive
How Does Optical Drive (CD/DVD/Blu-Ray) Work?
Optical Storage Differences
Optical Storage:
1. CD:
Can hold about 80 minutes of high quality music.
2. DVD
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has narrow pits, that's why it stores bigger data than CDs. New technology enables dual layer DVD to store double its size.
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a DVD can hold several hours of video.
3. Blue-ray
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has even smaller pits, that's why it stores more than DVDs or CDs. It can hold high-resolution video.
A CD / CD-R / DVD-R (R means read):
can only be written on once.
A CD-RW / DVD-RW (RW means rewritable):
can be written on many times.
Advantages of using optical drive:
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It's small, it doesn't take up too much space.
Disadvantages of using optical drive:
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It's easily scratched and cracked, so it becomes unusable.
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The writing process is called burn. Burning takes a long time.
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Data might be lost if we burn it many times.
Solid State Storage
How Does Flash Memory (Solid State Disk) work?
SSDs don't have magnetic device, so they're smaller than HDDs.
A USB flash is also a solid state.
Advantages:
Small, rewritable, stores a lot of data, fast.
Disadvantages:
There's no guarantee of long term use, after hundreds and hundreds of actions, they might start to lose data.
Cloud storage
How Cloud Storage work?
Some companies offer free cloud storage such as Google, Mega, OneDrive, DropBox, iCloud, MediaFire, etc.
Advantages:
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You don't need to buy your own storage media.
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You can access it any time you want with an internet connection.
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The data won't be lost because the cloud company has a backup storage themselves.
Disadvantages:
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Your data may not be private anymore.
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You can't access it if you don't have internet connection.
Oxford AQA IGCSE 2019
12.2
Explain one difference between main memory and secondary storage and state what each is used for. [3 marks]
Difference
__________________________________________________________________________
Main memory use
__________________________________________________________________________
Secondary storage use
__________________________________________________________________________
Alternative answers:
Difference:
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Main memory directly accessible by processor/CPU, while secondary storage not directly accessible by processor/CPU;
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Secondary storage is non-volatile, while main memory is volatile.
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main memory has faster access time, while secondary storage has slower access time
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Typically a computer has more secondary storage capacity, while a computer has less main memory capacity
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Main memory is inside the CPU, while secondary storage is external to the CPU (Note: Must be CPU not Processor)
Main Memory:
Stores programs/data currently in use;
Secondary Storage:
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Long-term storage of programs/data.
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Stores programs/data when computer turned off.
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Can be used to transfer programs/data between computers/devices.
12.2
Explain how an optical disc such as a CD box -ROM, DVD-ROM or Blu-ray represents data on a disc and how these data are read by an optical disc drive. [5 marks]
__________________________________________________________________________________
Alternative Answer:
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Data encoded by bumps/pits/lands/reflective/non-reflective spots on disc;
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Pit/land represent 1/0 or vice versa;
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Data organised in spiral track(s);
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Arm moves read/(write) head/laser over disc;
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Laser shines at data / track / disc; or use of laser
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Light reflects back;
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Light sensor detects reflected light;
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Difference of amount of reflected light indicates if 0 or 1 stored; or more reflected light = 1, less = 0 or vice-versa
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Data can be stored on multiple layers/sides of the discs (on some formats);
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Disc spins at constant linear velocity
Analyze and use your own words to simplify them.
Oxford AQA IGCSE 2020
15.1.
A school is thinking about moving its files to cloud storage. Discuss the advantages of this move for the school. You must include examples of situations in which the staff or students would benefit from this move in your response. [6 marks]
__________________________________________________________________________________
Alternative answers:
Advantages [3 marks]:
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The user can access their data from any device/location with an Internet connection;
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Enables user to more easily share data with others (can make parts of their cloud storage publicly available);
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Increases the amount of storage available/not restricted to the storage on the device;
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Facilitates collaborative work;
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No reliance on user to make backups;
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No need for user to implement security measures;
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Easily integrates with other cloud computing facilities;
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Can purchase devices with less secondary storage capacity, or no need to purchase servers / data storage;
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Less maintenance required
Examples [3 marks]:
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Teachers can easily share worksheets/resources with students;
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Students can collaborate with other students on projects;
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Students can complete work at home that they started in school (or vice-versa);
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Support staff have less need to manage security or have more time to perform other tasks;
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School may have lower costs for hardware;
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Reduced cost for support staff / maintenance;
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In subject where large files need to be stored such as media, these could be stored on the cloud;
Oxford AQA IGCSE Specimen Paper
05.1.
Explain how a magnetic hard disk drive stores data. [6 marks]
__________________________________________________________________________________
Answer key:
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Magnetic (medium);
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Binary digits/bits/0s and 1s/data represented by magnetising spots on disk // changing magnetic properties of disk;
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Disk made up of platter(s);
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Disk divided into tracks and sectors;
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A Either tracks or sectors alone Tracks are concentric circles // organised into cylinders;
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Drive head can move in/out // moves to track/cylinder // moves radially;
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Disk continuously spinning (while in operation);
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Disk spins at high speed // feasible example of speed;
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Data read/written as correct sector passes under read/write head;
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A Drive head. Data transferred in sectors/blocks;
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Medium and drive/device in sealed enclosure;
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Hard disk drive is a random access device;
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A Head parked / not over disk when not in use // head must not touch surface when in use;
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A Use of cache/buffer to speed up data transfer.
05.2.
Many modern laptop computers use a solid state disk for secondary storage instead of a magnetic hard disk drive. State two reasons why a solid state disk is more suitable for use in a laptop computer than a magnetic hard disk drive. [2 marks]
Reason 1:
__________________________________________________________________________________
Reason 2:
__________________________________________________________________________________
Oxford AQA IGCSE Mock Paper
06.1.
Explain why secondary storage is required in a computer. [2 marks]
__________________________________________________________________________________
06.2.
Discuss the advantages and disadvantages of using cloud storage instead of local storage such as a hard disk drive built into a computer. [4 marks]
__________________________________________________________________________________
