Know and understand fixed and portable solid-state drive (SSD) including SSD, pen drive, flash drive

Topic: Storage Devices and Media (Cambridge IGCSE ICT 0417)

What you must know

• Identify the three families of storage devices – magnetic, optical and solid‑state – and the related storage media.
• For each family describe:

  • Physical principle and basic structure
  • Typical capacities, interfaces and speed ranges
  • Power use and durability
  • Typical uses, advantages and disadvantages

• Distinguish internal (fixed) storage from backing (removable or external) storage and know when each is appropriate.

1. Overview of Storage Families

Cambridge groups storage devices into three families. Each family contains several devices (e.g., hard‑disk drive, CD‑ROM, SSD) and the corresponding media (e.g., magnetic platters, optical disc, flash memory).

• Magnetic storage – data recorded by magnetising tiny particles on a rotating medium.
• Optical storage – data recorded as pits & lands on a disc and read with a laser.
• Solid‑state storage – data stored in non‑volatile flash memory cells; no moving parts.

2. Magnetic Storage

2.1 Hard‑Disk Drive (HDD) – Internal & External

• Physical principle: Rotating magnetic platters with read/write heads that float on an air cushion.
• Typical capacities: 500 GB – 8 TB.
• Common interfaces: SATA (desktop/laptop), USB 3.x (external enclosures).
• Speed: 100 MB/s – 200 MB/s sequential; slower random access due to mechanical movement.
• Write cache & fragmentation: Modern HDDs use a small RAM cache to speed up writes; fragmentation can degrade performance and is a common exam topic.
• RAID relevance: HDDs are often used in RAID arrays for redundancy or performance – a point to evaluate in solution‑oriented questions.
• Power consumption: 6 W – 10 W (higher than SSDs).
• Durability: Sensitive to shock and vibration because of moving parts.
• Typical uses: Mass storage for PCs, servers and laptops; archival where cost per GB is a priority.

2.2 Magnetic Tape

• Physical principle: Long, thin plastic ribbon coated with magnetic particles; read/write by a tape drive.
• Typical capacities (compressed): 100 GB – 30 TB.
• Interface: Dedicated tape‑drive ports (often SCSI or Fibre Channel).
• Speed: 30 MB/s – 300 MB/s depending on tape type (e.g., LTO‑8).
• Power use: Low when idle; spikes during read/write.
• Durability: Very high for long‑term archival if stored correctly; not suited to frequent random access.
• Typical uses: Enterprise backup, off‑site archival, “cold” storage.

3. Optical Storage

3.1 CD, DVD, Blu‑ray

• Physical principle: Polycarbonate disc with pits & lands; read by a laser of appropriate wavelength.
• Typical capacities:

  • CD‑ROM: 700 MB
  • DVD‑R/DVD‑RW: 4.7 GB (single‑layer) / 8.5 GB (dual‑layer)
  • Blu‑ray BD‑R/BD‑RE: 25 GB (single‑layer) / 50 GB (dual‑layer)

• Interface: Built‑in IDE/SATA optical drive or external USB drive.
• Speed: 5 MB/s – 36 MB/s (depends on disc type and drive).
• Error‑correction: Reed‑Solomon coding provides resilience to minor scratches.
• Power consumption: 2 W – 5 W while spinning.
• Durability: Resistant to magnetic fields; vulnerable to scratches, heat and UV light.
• Typical uses: Software distribution, media playback, short‑term backup, small‑scale archival.

4. Solid‑State Storage

4.1 Fixed (Internal) SSD

• Technology: NAND flash memory chips managed by an SSD controller; no moving parts.
• Typical capacities: 128 GB – 4 TB.
• Interfaces: SATA (≈ 500 MB/s) or NVMe PCIe (≈ 3 500 MB/s).
• Key concepts:

  • Data retention – how long data stays without power.
  • Write‑endurance – limited program/erase cycles per cell.
  • Wear‑leveling – controller spreads writes evenly.

• Power consumption: 2 W – 5 W.
• Durability: Very high – immune to shock, vibration and magnetic fields.
• Typical uses: Operating system, applications, high‑performance data storage.

4.2 Portable SSD (External Enclosure)

• Technology: Same flash chips and controller as a fixed SSD, housed in a rugged case.
• Typical capacities: 256 GB – 2 TB.
• Interfaces: USB 3.0/3.1/3.2, USB‑C, Thunderbolt 3/4.
• Speed: 500 MB/s – 2 000 MB/s (limited by host interface).
• Power consumption: 1 W – 3 W (drawn from the host port).
• Durability: Shock‑resistant case; no moving parts.
• Typical uses: Laptop backup, transport of large video/graphics files, “backing storage” for mobile work.

4.3 Pen Drive (USB Flash Drive)

• Technology: NAND flash with a simple USB controller.
• Typical capacities: 4 GB – 256 GB (higher capacities now available).
• Interfaces: USB 2.0, USB 3.0, USB‑C.
• Speed: 30 MB/s – 150 MB/s (controller and USB bottleneck).
• Power consumption: ≤ 0.5 W (powered from the USB port).
• Durability: High – solid‑state, though the plastic key can break.
• Typical uses: Quick file transfer, portable presentations, temporary storage.

4.4 Memory Cards (SD, micro‑SD)

• Technology: NAND flash in a very small form factor; used in cameras, smartphones, tablets.
• Typical capacities: 2 GB – 1 TB (SD XC, micro‑SD XC).
• Interfaces: SD slot (UHS‑I, UHS‑II, UHS‑III) or micro‑SD slot; can be accessed via a USB card reader.
• Speed: 10 MB/s – 300 MB/s (depends on class and UHS rating).
• Typical uses: Storage for digital cameras, mobile devices, portable gaming consoles.

5. Comparison of Main Devices

6. Summary of Advantages & Disadvantages

Fixed SSD

• Advantages: Very fast random access, silent, low power, high durability.
• Disadvantages: Higher purchase price per GB; limited write‑endurance (mitigated by wear‑leveling).

Portable SSD

• Advantages: High speed in a compact, shock‑resistant case; ideal for backing up laptops or transporting large media files.
• Disadvantages: More expensive than USB pen drives; performance limited by host USB version.

Pen Drive (USB Flash)

• Advantages: Extremely portable, cheap, plug‑and‑play on any computer.
• Disadvantages: Slower than SSDs, lower write‑endurance, easy to misplace.

Memory Card (SD / micro‑SD)

• Advantages: Tiny form factor, widely used in cameras and mobile devices, moderate speed for media capture.
• Disadvantages: Limited capacity compared with SSDs, can be lost or damaged, speed varies by class.

Hard‑Disk Drive (HDD)

• Advantages: Large capacities at low cost; familiar technology; useful in RAID configurations for redundancy or performance.
• Disadvantages: Slower random access, vulnerable to shock, noisy, higher power draw; fragmentation can affect speed.

Optical Disc (CD/DVD/Blu‑ray)

• Advantages: Inexpensive for distribution, long‑term readability when stored properly, resistant to magnetic fields.
• Disadvantages: Limited capacity, slower data rates, prone to scratches, becoming less common.

Magnetic Tape

• Advantages: Very low cost per GB for archival, excellent longevity when stored correctly.
• Disadvantages: Slow random access, requires specialised drive, not suitable for everyday use.

7. Choosing the Right Device (Backing Storage vs. Internal Storage)

Use the checklist below when deciding which storage solution best fits a particular need. The points reflect the syllabus emphasis on “backing storage” (removable or external) versus “internal storage” (fixed inside the computer).

1. Purpose: OS & applications → internal SSD/HDD; backup/transport → portable SSD, pen drive, memory card, tape.
2. Capacity required: Small files (pen drive, memory card) vs. large data sets (HDD, portable SSD, tape).
3. Speed needed: Video editing, gaming → SSD/NVMe; occasional file transfer → USB 3.x pen drive.
4. Portability & durability: Field work → rugged portable SSD or high‑grade pen drive; office → internal HDD/SSD.
5. Budget considerations: Higher performance = higher cost; for long‑term archive, tape may be cheapest per GB.
6. Compatibility: Ensure the device’s interface (SATA, NVMe, USB‑C, SD slot, tape‑drive) matches the host computer.
7. Future‑proofing: Consider emerging standards (NVMe over PCIe 4.0/5.0, USB 4) if the budget allows.