Cambridge IGCSE0417

Storage devices and media

Information Communication Technology 0417 Chapter Notes

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Storage devices and media
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In this chapter

  1. 1Fundamentals of Computer Storage
  2. 2Magnetic Storage Devices
  3. 3Optical Storage Devices
  4. 4Solid-State Storage
  5. 5Comparing Storage Technologies
  6. 6Choosing the Right Storage Solution

1. Fundamentals of Computer Storage

Computer storage holds data and programs, even when the power is off. This is called non-volatile storage. It's different from RAM (Random Access Memory), which is volatile and loses its contents when the power is cut. Storage is also known as 'secondary storage'. We must distinguish between the 'storage medium', which is the physical material that holds the data (like a CD), and the 'storage device', which is the machinery that reads from and writes to the medium (like a CD drive).

Key term

Non-volatile memory: A type of computer memory that can retain stored information even after power is removed.

Examiner insight

Examiners look for precise use of terminology. Clearly distinguishing between the 'medium' (the disc/tape) and the 'device' (the drive) in your answers will gain credit.

Common pitfall

Confusing storage with memory. When someone asks about the 'memory' of a phone (e.g., 128GB), they are usually referring to its non-volatile storage capacity, not its RAM.

Worked example 13 marks

For a Blu-ray disc, identify the storage medium and the storage device. Explain the role of each.

  1. 1
    1. Identify the medium: The Blu-ray disc itself is the storage medium. This is because it is the physical object that holds the data.
  2. 2
    1. Identify the device: The Blu-ray player or drive is the storage device.
  3. 3
    1. Explain roles: The role of the Blu-ray disc (medium) is to physically store the data in the form of microscopic pits and lands. The role of the Blu-ray drive (device) is to use a laser to read this data from the disc and to write data to it (if it's a recordable disc).

Recap

  • Storage is non-volatile, meaning it keeps data when the power is off.
  • RAM is volatile memory, not storage.
  • The storage medium is the material that holds the data (e.g., a disk).
  • The storage device is the machine that reads and writes the data (e.g., a disk drive).

Quick check

  1. Is the internal hard drive of a computer an example of volatile or non-volatile memory?1 mark
  2. What is the general term for storage like hard drives, as opposed to primary memory like RAM?1 mark

2. Magnetic Storage Devices

Magnetic storage uses magnetic patterns to represent data. The surface of the medium (like a disk platter or tape) is coated with a magnetic material. A read/write head, which is a tiny electromagnet, moves over the surface. To write data, it alters the magnetic polarity of tiny spots on the surface to represent binary 1s and 0s. To read data, it detects the magnetic polarity of these spots. The main examples are Hard Disk Drives (HDDs) and magnetic tape.

Key term

Hard Disk Drive (HDD): A magnetic storage device that uses spinning platters coated with magnetic material and moving read/write heads to store and retrieve digital data.

Examiner insight

Examiners reward answers that link the mechanical nature of HDDs (spinning platters, moving heads) to their disadvantages, such as slower access times than SSDs and vulnerability to physical shock.

Common pitfall

Thinking magnetic tape is obsolete. It is still a primary choice for archiving massive datasets in large organisations due to its low cost, high capacity, and long-term durability when stored correctly.

Worked example 13 marks

A desktop computer used for video editing needs a large amount of storage. Suggest a suitable magnetic storage device and justify your choice with two advantages.

  1. 1
    1. Suggest device: A large internal Hard Disk Drive (HDD).
  2. 2
    1. Justification 1 (Capacity & Cost): HDDs offer very large storage capacities (e.g., several terabytes) at a very low cost per gigabyte. This is ideal for storing large video files.
  3. 3
    1. Justification 2 (Speed): While not as fast as an SSD, an internal HDD offers fast enough data access for most video editing tasks and is much faster than options like magnetic tape or optical discs.

Recap

  • Magnetic storage uses magnetic patterns on a surface to store data as 1s and 0s.
  • A read/write head magnetises or detects the magnetic state of the media.
  • Hard Disk Drives (HDDs) are a common example, using spinning magnetic platters.
  • Magnetic tape is also magnetic, used for large-scale backups and archives due to its high capacity and low cost.
  • Magnetic storage can be damaged by strong magnetic fields.

Quick check

  1. Name two devices that use magnetic storage.2 marks

3. Optical Storage Devices

Optical storage devices use a laser to read and write data. Data is stored as microscopic indentations ('pits') and flat surfaces ('lands') on a reflective disc. When the laser shines on the disc, lands reflect the light back strongly, while pits scatter the light. A sensor detects this difference in reflection to read binary 1s and 0s. Examples include Compact Discs (CDs), Digital Versatile Discs (DVDs), and Blu-ray Discs. The key difference between them is the laser wavelength; a Blu-ray's blue-violet laser is finer, allowing more data to be packed in. Discs come in three main types: ROM (Read-Only Memory), R (Recordable once), and RW (Rewritable).

Key term

Optical Storage: Storage that uses a laser to read and write data from a spinning disc by detecting reflections from microscopic pits and lands.

Common pitfall

Confusing the different types: CD-ROM (Read-Only), CD-R (Recordable once), and CD-RW (Rewritable). The suffix is crucial and determines what you can do with the disc.

Fun fact

The data track on a CD is a continuous spiral that, if unwound, would stretch for over 5 kilometres (about 3.5 miles).

Worked example 12 marks

Explain how a Blu-ray disc can store more data than a DVD.

  1. 1
    1. Identify the key technology: The difference is the laser used. Blu-ray uses a blue-violet laser, while DVDs use a red laser.
  2. 2
    1. Explain the physics: The blue-violet laser has a shorter wavelength than the red laser.
  3. 3
    1. Link to data storage: This shorter wavelength allows the laser to focus on a much smaller spot. This means the pits and lands on the disc can be made smaller and packed closer together, increasing the overall data density and storage capacity.

Recap

  • Optical devices use a laser to read data from pits and lands on a disc.
  • Examples include CDs (~700MB), DVDs (~4.7GB), and Blu-rays (~25-128GB).
  • Blu-ray holds more data because its blue-violet laser has a shorter wavelength.
  • ROM discs are read-only (e.g., a movie on DVD).
  • R discs can be written to once.
  • RW discs can be written to and erased multiple times.

Quick check

  1. What do the letters 'RW' in CD-RW stand for?1 mark
  2. List CD, DVD, and Blu-ray in order of capacity, from lowest to highest.1 mark

4. Solid-State Storage

Solid-state storage has no moving parts. It uses a type of non-volatile memory called 'flash memory', which consists of millions of transistors. Data is stored by trapping or releasing electrons in these transistors to represent 1s and 0s. Because there are no spinning disks or moving heads, accessing data is extremely fast. This technology is also very durable, resistant to physical shock, and consumes less power. Common examples include Solid-State Drives (SSDs), which are replacing HDDs in many computers, USB flash drives (memory sticks), and memory cards (like SD cards used in cameras and phones).

Key term

Solid-State Drive (SSD): A storage device that uses flash memory chips to store data, containing no moving mechanical parts, which makes it very fast and durable.

Examiner insight

High-scoring answers clearly explain *why* SSDs are faster and more durable by explicitly stating they have 'no moving parts', contrasting this with the 'spinning platters and moving read/write heads' of an HDD.

Fun fact

The 'flash' in flash memory was a name coined by its inventor at Toshiba, who thought the process of erasing the memory in a single flash was reminiscent of a camera flash.

Worked example 14 marks

A student uses a laptop for school. Explain two reasons why a Solid-State Drive (SSD) is a more suitable main drive for their laptop than a traditional Hard Disk Drive (HDD).

  1. 1
    1. Reason 1 (Durability/Portability): Laptops are portable and likely to be moved and knocked. An SSD has no moving parts, making it highly resistant to physical shock and damage, protecting the student's data. An HDD's moving parts are vulnerable to damage from knocks.
  2. 2
    1. Reason 2 (Speed/Performance): An SSD has much faster data access speeds. This means the laptop will boot up faster, applications will load quicker, and files will open almost instantly, improving the student's productivity and user experience.

Recap

  • Solid-state storage uses non-volatile flash memory and has no moving parts.
  • This makes it very fast, durable, and power-efficient.
  • Examples include Solid-State Drives (SSDs), USB flash drives, and memory cards.
  • SSDs are much faster than HDDs for booting up an OS and loading programs.
  • The main drawbacks are a higher cost per gigabyte and a limited number of write cycles (though this is not an issue for most users).

Quick check

  1. State the key physical difference between an SSD and an HDD.1 mark
  2. Name one device, other than an SSD, that uses solid-state storage.1 mark

5. Comparing Storage Technologies

Choosing the right storage involves trading off between different factors. There is no single 'best' type of storage; the best choice depends entirely on the job it needs to do. The key characteristics to compare are: Capacity (how much data it holds), Speed (how quickly data can be accessed), Portability (how easy it is to move), Durability (resistance to damage), Reliability (how long it lasts without failing), and Cost (price per gigabyte).

Key term

Cost per Gigabyte: A metric used to compare storage devices, calculated by dividing the total cost of the device by its storage capacity in gigabytes.

Examiner insight

Marks are often awarded for comparative statements. Instead of saying 'SSDs are fast', a better answer is 'SSDs have much faster data access speeds than HDDs because they have no moving parts'.

Worked example 14 marks

Compare a portable HDD and a USB flash drive for a student who needs to transfer a 10GB video project between home and school.

  1. 1
    1. Capacity: Both devices can easily store 10GB. A portable HDD will offer much higher total capacity (e.g., 1TB) for a similar price to a large USB drive (e.g., 128GB).
  2. 2
    1. Portability & Durability: The USB flash drive is much smaller, lighter, and more portable. As a solid-state device, it is also far more durable and resistant to being knocked around in a school bag compared to the mechanical portable HDD.
  3. 3
    1. Speed: The USB flash drive will likely offer faster transfer speeds for a single large file, but this can vary by model. Both are adequate for the task.
  4. 4
    1. Conclusion: For this task, the USB flash drive is the better choice due to its superior portability and durability, which are key for a student's daily use, even if the HDD offers better cost per GB.

Recap

  • SSDs are the fastest, most durable, and most portable, but also the most expensive per GB.
  • HDDs offer the highest capacities for the lowest cost per GB, making them ideal for mass storage, but are slower and less durable.
  • Optical discs are very cheap to produce for software or media distribution, but are slow, have limited capacity, and are easily scratched.
  • Magnetic tape offers huge capacity for a very low cost, but has very slow access speeds (serial access), making it suitable only for archival backups.

Quick check

  1. Which storage technology generally has the lowest cost per gigabyte?1 mark
  2. Which storage technology offers the fastest data access speeds?1 mark

6. Choosing the Right Storage Solution

Applying your knowledge is key. When faced with a scenario, you must choose the most suitable storage device and justify your choice. Think about the C-C-S-P-D-R factors: Cost, Capacity, Speed, Portability, Durability, and Reliability. For example, for a main operating system drive, Speed is critical (choose SSD). For archiving a company's entire financial history, Capacity and low Cost are key (choose magnetic tape or HDD). For giving a friend a few photos, low Cost and convenience are important (choose USB flash drive or cloud storage).

Key term

Backup: A copy of data kept in a separate location so that it can be restored if the original data is lost or corrupted.

Examiner insight

To gain full marks in scenario questions, you must not only name a suitable device but also justify your choice with reasons linked to the scenario's specific needs (e.g., 'A USB flash drive is suitable because it is portable for carrying between home and school, and durable enough for a school bag').

Worked example 13 marks

A photographer needs a device to back up large photo files from their main computer each day. They need high capacity and reliability. Suggest a suitable storage device and justify your choice.

  1. 1
    1. Identify key requirements: The scenario requires high capacity (for large photo files) and reliability for daily backups.
  2. 2
    1. Suggest device: An external Hard Disk Drive (HDD).
  3. 3
    1. Justification 1 (Capacity/Cost): External HDDs provide very large storage capacities (e.g., 4TB or more) for a relatively low price. This is perfect for storing thousands of high-resolution photos without running out of space quickly.
  4. 4
    1. Justification 2 (Reliability): HDDs are a proven, reliable technology for long-term storage when handled correctly. Using an external drive allows the photographer to keep the backup physically separate from the main computer, which is good practice.

Worked example 24 marks

A school uses portable data loggers to measure temperature in an outdoor experiment. The devices are small and battery-powered. Explain why solid-state storage is the most suitable for these data loggers.

  1. 1
    1. Analyse the scenario: The data loggers are portable, used outdoors, and battery-powered.
  2. 2
    1. Reason 1 (Durability): Because they are used outdoors and are portable, the devices may be dropped or knocked. Solid-state storage has no moving parts, making it highly shock-resistant and durable, which is essential in this environment.
  3. 3
    1. Reason 2 (Power Consumption): The data loggers are battery-powered. Solid-state storage consumes significantly less power than a magnetic hard drive, which means the data logger's battery will last longer during the experiment.

Recap

  • Always link your choice of storage to the specific needs of the scenario.
  • Justify your choice using at least two relevant factors (e.g., capacity, speed, portability).
  • For backups, consider capacity, reliability, and cost.
  • For portable devices, consider durability, size, and power consumption.
  • For a computer's main drive, speed is the most important factor for performance.

Quick check

  1. What would be the most suitable storage medium to distribute a new piece of software to 1000 customers?1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Explain the difference between a storage device and a storage medium, using a CD as your example.2 marks
  2. State three characteristics of solid-state storage.3 marks
  3. A film company needs to send a high-definition movie file (approx. 80GB) to a production house. Compare the suitability of using a Blu-ray disc versus an external solid-state drive (SSD) for this task.4 marks
  4. Describe how data is written to and read from a magnetic hard disk drive.4 marks
  5. Identify two disadvantages of using magnetic storage compared to solid-state storage.2 marks
  6. A large corporation needs to create a weekly backup of its entire server data, which amounts to several terabytes. Speed of backup is not critical, but cost and capacity are the most important factors. Suggest the most suitable storage medium and justify your choice.3 marks
  7. Explain why a solid-state drive (SSD) allows a computer to boot up faster than a hard disk drive (HDD).3 marks
  8. A software company is releasing a new application. They are considering distributing it on either CD-ROM or DVD-ROM. Describe a factor that would determine which one they should choose.2 marks
  9. A user complains their new laptop with a 1TB HDD is much slower than their old phone with 128GB of storage. Explain the technological reason for this difference in performance.4 marks
  10. For each of the following scenarios, state the most appropriate storage device: (a) Storing the operating system of a modern, high-performance laptop. (b) Archiving 50 years of a university's student records. (c) Giving a classmate a copy of a 200MB presentation.3 marks

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