Know and understand magnetic drives including fixed and portable magnetic hard drives, magnetic tape drives

Storage Devices and Media – Magnetic, Optical and Solid‑State

Device vs. Media (Cambridge IGCSE ICT definition) – A storage device is the hardware that reads or writes data (e.g., a hard‑disk drive, a DVD‑ROM, a USB flash drive). The storage media is the material that actually holds the information (e.g., a magnetic platter, an optical disc, a flash‑memory chip). Both terms appear in exam questions, so the distinction is highlighted throughout these notes.

1. Magnetic Storage

1.1 Fixed (Internal) Magnetic Hard Drives (HDD)

• Device: Mounted inside the computer chassis; connects to the motherboard via SATA, IDE or NVMe.
• Media: One or more circular platters coated with a thin iron‑oxide magnetic layer.
• Key components

  • Platters – magnetic surface where bits are stored.
  • Spindle motor – rotates the platters (typically 5400 rpm or 7200 rpm for desktops, up to 15 000 rpm for servers).
  • Read/Write heads – tiny electromagnets that change or sense the magnetic polarity of each bit.
  • Actuator arm (voice coil) – moves the heads radially to reach any track.
  • Controller board – translates data between the computer’s bus and the heads; includes cache memory.

• Advantages

  • High capacity (several TB) at low cost per gigabyte.
  • Random‑access – fast seek times for everyday tasks.
  • Well‑established, widely compatible technology.

• Disadvantages

  • Moving parts are vulnerable to shock, vibration and wear.
  • Higher power consumption than solid‑state alternatives.
  • Audible noise from spinning platters and actuator movement.

School example: A lab PC uses a 1 TB internal HDD to store the operating system, teaching software and students’ work files.

1.2 Portable (External) Magnetic Hard Drives

• Device: An internal HDD placed in a protective enclosure with an external connector.
• Media: Same magnetic platters as a fixed HDD.
• Common interfaces

  • USB 2.0 (480 Mbps)
  • USB 3.0 / 3.1 (5 Gbps – 10 Gbps)
  • eSATA (6 Gbps)
  • Thunderbolt (up to 40 Gbps)

• Power source

  • Bus‑powered via USB (most 2.5‑in models).
  • External AC adapter for larger 3.5‑in units.

• Advantages

  • Portable – ideal for backups or moving large files between computers.
  • Plug‑and‑play with Windows, macOS and Linux.
  • Capacities comparable to internal drives.

• Disadvantages

  • Moving parts make it vulnerable to drops and bumps.
  • Generally slower than SSD‑based portable drives.
  • Requires a physical cable; no built‑in wireless.

School example: A student copies a video project from the school PC onto a 2 TB external HDD to continue editing at home.

1.3 Magnetic Tape Drives

• Device: A drive that pulls a magnetic tape past a stationary read/write head.
• Media: Long, thin strip of magnetic material wound on a cartridge or reel (e.g., LTO, DAT).
• Common formats

  • DAT (Digital Audio Tape) – small cassette, used for modest backups.
  • LTO (Linear Tape‑Open) – cartridge system; current generation LTO‑9.
  • Reel‑to‑reel – large‑scale archival systems.

• How it works

  • Tape is unwound from a supply reel, passes over the head, and is wound onto a take‑up reel.
  • Data are recorded in linear tracks; modern LTO uses many parallel tracks per pass, dramatically increasing capacity.

• Advantages

  • Very high capacity per cartridge (up to 30 TB compressed for LTO‑9).
  • Low cost per gigabyte – ideal for long‑term archival.
  • Stable when stored correctly; resistant to electromagnetic interference.

• Disadvantages

  • Sequential access – slower for random reads/writes.
  • Requires a dedicated tape drive and management software.
  • Physical wear of the tape and head after many passes.

School example: The ICT department uses an LTO‑6 drive to archive yearly exam papers and project files for up to ten years.

1.4 Backup & Redundancy (Key for the IGCSE “Storage” and “Networks” sections)

• RAID (Redundant Array of Independent Disks)

  • RAID 0 – Striping for speed, no redundancy.
  • RAID 1 – Mirroring; identical copy on two disks – provides fault tolerance.
  • RAID 5 – Striping with parity; needs ≥ 3 disks; balances capacity, speed and fault tolerance.

  Typical school use: a small server with two 2 TB drives in RAID 1 to protect critical data.

• External backup – Portable HDD or USB flash drive used to create regular copies of important files.
• Cloud backup – Data stored on remote servers accessed via the Internet (e.g., Google Drive, OneDrive). Provides off‑site protection and easy sharing.
• Backup schedule (exam‑friendly tip)

  • Daily incremental backup + weekly full backup.
  • Store at least one copy off‑site (cloud or external media).

2. Optical Storage

2.1 CD‑ROM / CD‑R / CD‑RW

• Device: Optical disc drive that spins a 120 mm disc and uses an infrared laser (780 nm) to read or write data.
• Media

  • CD‑ROM – pre‑pressed, read‑only.
  • CD‑R – write‑once.
  • CD‑RW – rewriteable (≈ 1 000 cycles).

• Key specs

  • Capacity: 700 MB (≈ 80 min audio).
  • Transfer rate: 150 KB/s (1×) – up to 10 MB/s at 72×.

• Advantages – Low cost, widely compatible, physical medium easy to label.
• Disadvantages – Limited capacity, vulnerable to scratches, slower sequential access.

2.2 DVD‑ROM / DVD‑R / DVD‑RW / DVD‑R‑DL

• Device: Similar to a CD drive but uses a red laser (650 nm) and reads/writes 12 cm or 8 cm DVDs.
• Media

  • DVD‑ROM – read‑only.
  • DVD‑R – single‑write, 4.7 GB.
  • DVD‑R‑DL – dual‑layer, 8.5 GB.
  • DVD‑RW – rewriteable (≈ 4.7 GB).

• Key specs

  • Capacity: 4.7 GB (single‑layer) or 8.5 GB (dual‑layer).
  • Transfer rate: 1.32 MB/s (1×) – up to 10 MB/s at 8×.

• Advantages – Larger capacity than CDs; still inexpensive and compatible with most school computers.
• Disadvantages – Same handling issues as CDs; declining use as USB and cloud storage become dominant.

2.3 Blu‑ray (BD‑ROM / BD‑R / BD‑RE)

• Device: High‑density optical drive using a blue‑violet laser (405 nm).
• Media

  • BD‑ROM – read‑only.
  • BD‑R – write‑once (25 GB single‑layer, 50 GB dual‑layer).
  • BD‑RE – rewriteable (same capacities).

• Key specs

  • Capacity: 25 GB (single‑layer) or 50 GB (dual‑layer).
  • Transfer rate: 36 Mbps (1×) – up to 54 Mbps (1.5×) in common drives.

• Advantages – High capacity suitable for HD video or large software packages; better scratch resistance than CD/DVD.
• Disadvantages – More expensive drives and discs; not yet standard in many school computers.

School example: A teacher distributes a 3 GB educational video on a DVD‑R for students to view on any school computer.

3. Solid‑State Storage

3.1 Solid‑State Drives (SSD)

• Device: Internal storage that uses NAND flash memory chips instead of rotating platters.
• Media: Flash memory cells (NAND) soldered onto a printed‑circuit board; no moving parts.
• Form factors & interfaces

  • 2.5 in SATA SSD – same connector as HDDs.
  • M.2 SATA – thin card that plugs into an M.2 slot.
  • M.2 NVMe (PCIe) – uses the PCIe bus for much higher bandwidth.
  • U. FS (Universal Flash Storage) – emerging standard for mobile devices.

• Key specs (SATA vs. NVMe)

  Spec	SATA III SSD	NVMe (PCIe 3.0 ×4) SSD
  Capacity	120 GB – 4 TB	256 GB – 8 TB
  Sequential read	500 MB/s – 560 MB/s	2 GB/s – 5 GB/s
  Sequential write	450 MB/s – 540 MB/s	1.5 GB/s – 4.5 GB/s
  Random I/O latency	0.1 ms – 0.2 ms	≤ 0.05 ms
  Power (idle/active)	≈ 0.5 W / 2 W	≈ 0.7 W / 5 W

• Advantages

  • Very fast boot‑up and application loading.
  • Silent operation – no moving parts.
  • More resistant to drops and vibration.

• Disadvantages

  • Higher cost per gigabyte than magnetic HDDs.
  • Limited write‑endurance (though ample for typical school use).

School example: The newest school laptops are equipped with 512 GB NVMe SSDs, allowing Windows to start in under 10 seconds.

3.2 USB Flash Drives (Pen drives)

• Device: Small, portable plug‑in containing a flash‑memory chip and a USB connector.
• Media: NAND flash memory.
• Typical specs

  • Capacity: 4 GB – 256 GB (common in classrooms).
  • Interface: USB 2.0 (480 Mbps) or USB 3.0/3.1 (5 Gbps – 10 Gbps).
  • Transfer rate: 20 MB/s – 150 MB/s depending on USB version.

• Advantages – Highly portable, plug‑and‑play, low cost for small capacities.
• Disadvantages – Easy to lose, connector wear with frequent use, security risk if not encrypted.

School example: Students submit coursework by copying the file onto a 16 GB USB flash drive and handing it to the teacher.

3.3 Memory Cards (SD, microSD, CompactFlash)

• Device: Small cards used mainly in cameras, tablets and some laptops.
• Media: NAND flash memory similar to USB drives.
• Typical specs

  • SD (Standard) – up to 2 TB (SDXC); speeds up to 300 MB/s (UHS‑III).
  • microSD – up to 1 TB; speeds up to 285 MB/s (UHS‑III).
  • CompactFlash – up to 512 GB; used in professional video equipment.

• Advantages – Very compact; many devices have built‑in slots.
• Disadvantages – Small size makes them easy to misplace; performance varies widely between classes.

4. Emerging & Network‑Based Storage (Link to the “Networks” syllabus section)

4.1 Cloud Storage

• Definition: Data stored on remote servers accessed via the Internet; the provider manages hardware, redundancy and backups.
• Common services – Google Drive, Microsoft OneDrive, Dropbox, iCloud.
• Key benefits for schools

  • Off‑site backup – protects against local hardware failure or theft.
  • Easy sharing and collaboration (e.g., students work on the same document simultaneously).
  • Scalable – add more storage without buying new hardware.

• Considerations

  • Requires reliable Internet connectivity.
  • Data security and privacy – use strong passwords and, where possible, encryption.
  • Ongoing subscription costs versus one‑off hardware purchase.

4.2 Network‑Attached Storage (NAS)

• Device: A dedicated file server containing one or more HDDs/SSDs, connected to the school network via Ethernet.
• Typical uses

  • Centralised file sharing for teachers and students.
  • Automatic backups of lab computers.
  • Media streaming within the school.

• Advantages – Provides RAID protection, can be accessed by many users, and simplifies backup management.
• Disadvantages – Requires network infrastructure and a modest amount of technical administration.

School example: The ICT department runs a 4‑bay NAS with two 4 TB drives in RAID 1, offering a shared “Resources” folder for all teachers.

5. Summary Table – Quick Comparison of Main Storage Types

Use this table to compare options when answering exam questions that ask you to recommend a storage solution for a given scenario.