Storage devices and media
Magnetic, optical and solid-state backing storage, how they work, their uses, and why backups are needed.
📌 Key points
- Backing storage keeps data permanently (non-volatile); the device reads and writes the data and the media is what the data is stored on (e.g. a DVD in a DVD drive).
- Magnetic storage: a hard disk drive (HDD) has spinning platters and read/write heads; it has a large capacity and low cost per GB, but has moving parts that can be damaged. HDDs are used in servers and desktop computers.
- Magnetic tape has a very large capacity and a low cost, but uses serial access (data is read in order from the start), so it is slow to find a file; it is used for backing up and archiving large amounts of data.
- Disks give direct access: any piece of data can be found straight away without reading through the rest.
- Optical storage (CD, DVD, Blu-ray) is read and written with a laser. Typical capacities: CD about 700 MB, DVD about 4.7 GB (single layer), Blu-ray about 25 GB (single layer); Blu-ray uses a blue laser with a shorter wavelength so data is packed more closely.
- Optical discs can be ROM (read-only, e.g. films and software for sale), R (recordable once, e.g. archives) or RW (rewritable many times).
- Solid-state storage (SSD, USB flash drive, memory cards such as SD cards) uses flash memory with no moving parts: fast access, robust, light, low power use, but more expensive per GB and it can only be rewritten a limited number of times.
- A backup is a copy of data kept separately (e.g. off-site or in the cloud) so it can be restored if the original is lost, corrupted, deleted, stolen or damaged.
📖 Key terms
- Storage medium
- The material that data is stored on, e.g. a disk or a tape.
- Serial access
- Data must be read in order from the beginning until the required item is reached.
- Direct access
- Data can be read straight away from any location without reading the data before it.
- Optical storage
- Storage that uses a laser to read and write data on a disc.
- Solid-state storage
- Storage that uses flash memory and has no moving parts.
- Backup
- A copy of data kept in case the original is lost or damaged.
✏️ Worked example
A photographer needs storage for a camera and a way to keep years of photos safe. Recommend storage for each.
- In the camera: a solid-state memory card (e.g. SD card).
- It is small, light, uses little power, is robust and has fast access, so photos are saved quickly.
- For long-term safety: back up the photos to an external hard disk or the cloud.
- Keep the backup in a different place from the original so a fire or theft does not destroy both.
For "which storage" questions, give a reason linked to the use: capacity, speed of access, portability, durability or cost. "Because it is better" earns nothing.
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