Understanding the three main categories in the Cambridge IGCSE 0417 syllabus – magnetic, optical and solid‑state – is essential for choosing the right storage solution. The sections below cover the required hardware types, key characteristics, typical uses, advantages and disadvantages, and a concise comparison.
Data are recorded by magnetising tiny domains on a ferromagnetic surface. Magnetic media dominate secondary storage because they provide the best capacity‑for‑price ratio.
| Characteristic | Typical Use | Advantages | Disadvantages |
|---|---|---|---|
| Medium – ferromagnetic coating on rotating platters (HDD) or on a moving tape (DAT, LTO) | Desktop PCs, laptops, servers (HDD); archival backup, disaster‑recovery (tape) | High capacity for price; mature, widely supported; large sequential transfer rates (HDD) | Mechanical wear; slower random‑access than SSD; vulnerable to magnetic fields; tape needs careful handling |
| Read/write method – magnetic heads alter polarity of domains (HDD) or glide over tape (contact‑less) | Random‑access storage (HDD) and sequential‑access backup (tape) | Random access on HDD enables fast file retrieval; tape offers very high native capacity per cartridge | Seek time and rotational latency increase with platter size; tape access time is long because of sequential nature |
| Form factors • 3.5‑inch (desktop) • 2.5‑inch (laptop/portable) • 1.8‑inch (ultra‑portable) • External USB enclosures • Tape cartridges (DAT, LTO) | Desktop storage, portable external drives, enterprise backup libraries | Variety of sizes fits many devices; external drives are plug‑and‑play | Physical size can limit portability; external drives need power; tapes need a drive and careful loading |
| Capacity ranges • HDD: 500 GB – 10 TB (single drive) • Tape: 80 GB – 45 TB (per cartridge, LTO generation dependent) | Primary storage (HDD) and long‑term archival (tape) | Scalable – add more drives or cartridges as needed | Large HDDs are heavier; tape cartridges must be stored in a controlled environment to avoid degradation |
| Access speed • HDD: 5‑12 ms average seek, 100‑200 MB/s sustained • Tape: 100‑200 MB/s sequential, but high latency due to winding | Everyday computing (HDD); bulk backup and restore (tape) | HDD provides reasonable random‑access speed; tape excels at bulk data transfer | HDD slower than SSD; tape unsuitable for frequent random reads/writes |
| Power consumption (typical) | Desktop/server HDDs, portable HDDs, tape drives | HDDs: 5‑10 W (idle) to 15‑20 W (active); tape drives: 30‑50 W during operation – acceptable for stationary use | Higher than SSDs; impacts battery life in laptops and energy costs in data centres |
Data are stored as pits (representing 0) and lands (representing 1) on a reflective disc surface. A low‑power laser reads the pattern.
| Format | Laser wavelength | Typical capacity (single layer) | Media variants | Typical use |
|---|---|---|---|---|
| CD‑ROM / CD‑R / CD‑RW | 780 nm (infra‑red) | ≈ 700 MB | Read‑only (ROM), write‑once (R), rewritable (RW) | Music, small software distribution, archival of documents |
| DVD‑ROM / DVD‑R / DVD‑RW / DVD‑R‑DL | 650 nm (red) | 4.7 GB (single‑layer) – 8.5 GB (dual‑layer) | Read‑only, write‑once, rewritable, dual‑layer (DL) | Video, larger software packages, backup of moderate‑size data sets |
| Blu‑ray (BD‑ROM / BD‑R / BD‑RE) | 405 nm (blue‑violet) | 25 GB (single‑layer) – 50 GB (dual‑layer) | Read‑only, write‑once, rewritable (RE) | High‑definition video, large software, high‑capacity archival |
| Aspect | Advantages | Disadvantages |
|---|---|---|
| Cost | Read‑only discs are very cheap; media are inexpensive to produce. | Recordable/re‑writable media cost more per GB than magnetic HDDs. |
| Durability | Resistant to magnetic fields; long shelf life (10‑20 years) when stored properly. | Surface scratches, exposure to sunlight or extreme temperatures can render data unreadable. |
| Capacity & Speed | Suitable for distribution of software, music and video. | Lower capacity and slower data rates (≈10‑100 MB/s) compared with HDD/SSD. |
| Write cycles | Write‑once (R) media are reliable for archival; rewritable (RW/RE) media allow multiple uses. | Re‑writable media have limited rewrite cycles (≈1 000‑10 000), after which errors may appear. |
Data are stored in non‑volatile flash memory cells; there are no moving parts, giving SSDs their speed and shock resistance.
| Characteristic | Typical Use | Advantages | Disadvantages |
|---|---|---|---|
| Medium – NAND flash memory (SATA, NVMe, USB, SD, eMMC, UFS) | Laptops, tablets, smartphones, high‑performance servers, portable storage | Very fast read/write (500 MB/s – >3 GB/s), low latency, silent, shock‑resistant | Higher cost per GB than magnetic; limited write‑endurance (improving with newer cells) |
| Form factors | Internal primary storage, external portable drives, camera storage, embedded device storage | Compact, lightweight, low power consumption | Data retention can degrade if left unpowered for many years, especially on low‑cost drives |
| Interface speed • SATA III = 6 Gb/s (≈550 MB/s) • PCIe 3.0 × 4 = 32 Gb/s (≈3 GB/s) • PCIe 4.0 × 4 = 64 Gb/s (≈7 GB/s) • USB 3.2 Gen 2 = 10 Gb/s | Gaming, video editing, scientific computing, rapid OS boot | Performance scales with newer interfaces; backward compatible (though at reduced speed) | Older computers may lack NVMe/PCIe 3.0/4.0 slots, limiting maximum speed |
| Power consumption (typical) | Mobile devices, laptops, desktops, data‑centre servers | SSD: 0.5‑2 W (idle) to 3‑5 W (active); USB flash: <1 W; eMMC/UFS: <0.5 W – excellent for battery life | Higher‑performance NVMe drives draw more power than SATA SSDs, affecting thermal design |
The table highlights the most important criteria for the three storage categories.
| Criteria | Magnetic | Optical | Solid‑state |
|---|---|---|---|
| Typical capacity (per unit) | 500 GB – 10 TB (HDD); 80 GB – 45 TB (tape) | 0.7 GB – 25 GB (CD‑DVD‑Blu‑ray) | 128 GB – 8 TB (SSD, flash drives, memory cards) |
| Cost per GB (approx.) | Low | Very low for read‑only; moderate for recordable/re‑writable | Higher (but falling rapidly) |
| Access speed | ≈100‑200 MB/s (HDD); sequential 100‑200 MB/s (tape, high latency) | ≈10‑100 MB/s (CD/DVD/BD) | ≈500 MB/s (SATA SSD) – >3000 MB/s (NVMe PCIe 4.0) |
| Power consumption | 5‑20 W (HDD); 30‑50 W (tape drive) when active | ≈1‑2 W (disc drive) – negligible when idle | 0.5‑5 W depending on interface and workload |
| Durability | Susceptible to shock, magnetic fields; moving parts wear | Resistant to magnetic fields; surface scratches are critical | Highly shock‑resistant; no moving parts; data retention may fall after long unpowered periods |
| Typical uses | Primary computer storage, enterprise servers, large‑scale backup (tape) | Media distribution, long‑term archival, software install discs | OS & applications drive, high‑performance workloads, portable data carriers |
Include a labelled hierarchy diagram that shows the three storage levels and typical capacity ranges. A simple SVG or hand‑drawn sketch works well.
Use icons for each type (disk, disc, chip, cloud) and annotate the typical capacity range next to each icon.