Know and understand characteristics, uses, media, advantages and disadvantages of storage devices including magnetic, optical and solid-state

Storage Devices and Media

Learning objective

Know and understand the characteristics, uses, media types, advantages and disadvantages of the three storage technologies required by the Cambridge IGCSE ICT specification (magnetic, optical and solid‑state). Be able to compare them and evaluate which is most suitable for a given situation, linking the choice to file‑management and data‑protection strategies (including the 3‑2‑1 backup rule).

Key terminology (AO1)

• Non‑volatile – retains data when power is removed.
• Capacity – amount of data a device can store (usually expressed in megabytes, gigabytes or terabytes).
• Access time / latency – time taken to locate and retrieve data.
• Read‑only vs. rewritable – whether data can be changed after it has been written.
• Wear‑leveling – technique used in flash memory to spread write‑erase cycles evenly across cells.
• MTBF (Mean Time Between Failures) – statistical estimate of reliability.

1. Characteristics of Magnetic Storage

1.1 Characteristics

• Data stored by magnetising tiny regions on a ferromagnetic surface.
• Read/write heads float on an air‑bearing (hard‑disk drives) or contact the surface (floppy disks, tape).
• Rotating platters (typically 5400 – 7200 rpm for desktop HDDs) determine access speed.
• Non‑volatile – data remains when power is removed.

1.2 Uses

• Primary storage in most desktop and laptop computers.
• External backup drives for home or small‑business data protection.
• Large‑capacity archival storage on magnetic tape (e.g., LTO).
• Legacy systems that still require floppy disks for firmware or boot media.

1.3 Media

• Internal hard‑disk drive (HDD) – sealed 2.5 in (laptop) or 3.5 in (desktop) unit.
• External HDD – portable enclosure with USB, eSATA or Thunderbolt.
• Floppy disk – 3.5 in flexible magnetic disk (1.44 MB).
• Magnetic tape – linear strip on reels or cartridges (e.g., LTO‑8 up to 30 TB native).

1.4 Advantages

• High capacity at a low cost per gigabyte.
• Well‑established technology – compatible with virtually all computers.
• Re‑writable many thousands of times; tape can be erased and reused.
• Suitable for large, infrequently accessed archives.

1.5 Disadvantages

• Moving parts are vulnerable to shock, vibration and wear.
• Access times (≈ 5‑10 ms) slower than solid‑state media.
• Higher power consumption because platters must spin.
• Strong magnetic fields can corrupt data.

2. Characteristics of Optical Storage

2.1 Characteristics

• Data encoded as pits (low) and lands (high) on a reflective polymer layer.
• A laser reads the pattern by detecting changes in reflected light; a higher‑power laser writes on recordable media.
• Non‑volatile – data remains without power.
• Typical laser wavelengths: 780 nm (CD), 650 nm (DVD), 405 nm (Blu‑ray).

2.2 Uses

• Distribution of software, music, movies and other media.
• Long‑term archival copies (master copies of video or software).
• Portable data exchange where a cheap, universal reader is required.

2.3 Media

• CD‑ROM / CD‑R / CD‑RW – up to 700 MB.
• DVD‑ROM / DVD‑R / DVD‑RW / DVD‑RDL (dual‑layer) – 4.7 GB (single) or 8.5 GB (dual).
• Blu‑ray Disc (BD‑ROM / BD‑R / BD‑RE) – 25 GB (single) or 50 GB (dual).
• Archival‑grade discs (e.g., M‑Disc) – designed for ≥ 30 years storage.

2.4 Advantages

• Immune to magnetic fields and most electromagnetic interference.
• Relatively inexpensive for moderate capacities; cheap to mass‑produce.
• Easy to distribute – most computers and many standalone players can read them.
• Archival‑grade discs offer long data‑retention when stored correctly.

2.5 Disadvantages

• Limited capacity compared with modern HDDs and SSDs.
• Write speeds are slower; many discs are read‑only.
• Surface is vulnerable to scratches, dust and laser degradation.
• Older drives may not read newer high‑density formats.

3. Characteristics of Solid‑State Storage

3.1 Characteristics

• Data stored in NAND flash memory cells; no moving parts.
• Access times measured in microseconds (≈ 0.1‑0.5 ms), far faster than magnetic media.
• Non‑volatile, but each cell has a finite number of program/erase (P/E) cycles.
• Controller provides wear‑leveling, error‑correction codes (ECC) and TRIM support.

3.2 Uses

• Primary storage in laptops, tablets, ultrabooks and high‑performance desktops.
• External portable drives for rapid data transfer and on‑the‑go editing.
• Embedded storage in smartphones, digital cameras, drones and IoT devices.
• Cache in servers and high‑speed workstations (NVMe SSDs).

3.3 Media

• 2.5‑inch SATA SSD – uses the same interface as a traditional HDD.
• M.2 SATA SSD – thin card that plugs into an M.2 slot, still SATA‑based.
• M.2 NVMe (PCIe) SSD – uses the PCIe bus for up to 7 GB/s bandwidth.
• USB flash drive – removable, typically USB‑A or USB‑C.
• Secure Digital (SD, micro‑SD) cards – used in cameras, phones and some laptops.

3.4 Advantages

• Very fast read/write speeds and low latency.
• Robust – no moving parts, resistant to shock and vibration.
• Low power consumption; ideal for battery‑operated devices.
• Quiet operation – no audible spin‑up or seek noise.

3.5 Disadvantages

• Higher cost per gigabyte than magnetic storage.
• Finite write‑endurance; each cell can only endure a limited number of P/E cycles (mitigated by wear‑leveling).
• Data recovery after a catastrophic failure is more complex and often uneconomic.
• Performance can degrade as the drive fills up if TRIM is not supported.

4. Comparison of the Three Technologies

5. Linking Storage Choice to File‑Management & Data‑Protection (AO2/AO3)

When selecting a storage medium, students should apply the 3‑2‑1 backup rule (three copies of data, on two different media types, with one copy stored off‑site). The rule dovetails with syllabus sections 11‑16 (file formats, compression, proofing, security, backup and recovery).

Example school‑level backup plan

1. Primary working files – stored on an internal SSD (fast access for editing and research). Files are saved in appropriate formats (e.g., .docx, .xlsx, .png) and compressed where sensible (e.g., weekly .zip archives of project folders).
2. Local backup – an external 4 TB HDD connected via USB‑3.0, scheduled to run a nightly incremental backup using the school’s backup software.
3. Off‑site/archival backup – an annual copy written to an archival‑grade Blu‑ray disc (or LTO tape if the school has a drive) and stored in a locked fire‑proof cabinet at a different location.

This approach satisfies the 3‑2‑1 rule, uses two different media (magnetic and optical), and demonstrates good file‑organisation (consistent naming, folder hierarchy, use of compression).

6. Emerging Storage Technologies (optional further reading)

7. Summary checklist (AO1 – AO3)

1. Identify the physical principle used to store data (magnetism, light reflection, electrical charge).
2. Match each storage type with typical capacities, speeds and common applications.
3. Recall at least two advantages and two disadvantages for magnetic, optical and solid‑state storage.
4. Use the comparison table to evaluate which medium best fits a given scenario (e.g., high speed vs. low cost vs. long‑term archival).
5. Explain how the chosen storage fits into a broader file‑management and backup strategy, referencing the 3‑2‑1 rule and relevant syllabus sections (11‑16).
6. Describe one emerging technology and its potential impact on future storage solutions.