Storage
Comparing Storage Devices
To compare storage devices and media fairly, you use six characteristics: capacity, speed, portability, durability, reliability and cost. Each one shows a different strength or weakness, so a fair comparison uses all six.
- Capacity — how much data the device or medium can hold.
- Speed — how quickly data can be written to it and read back from it.
- Portability — how easily it can be carried somewhere else and connected to another device, including its size and weight.
- Durability — how well it resists physical harm such as drops, knocks, vibration, scratches, heat and magnets.
- Reliability — how dependably it keeps working and keeps data intact, without errors, over long periods and repeated use.
- Cost — the purchase price, and above all the price of each gigabyte stored.
How the types compare
| Characteristic | Magnetic HDD | Solid state | Optical disc | Magnetic tape |
|---|---|---|---|---|
| Capacity | High | High | Low | Very high |
| Speed | Slower than solid state | Fastest | Slow | Slowest at finding one file |
| Portability | Fixed drives stay in the case; portable ones are bulky | Small, light, easy to connect | Thin and light but needs a drive | Needs a drive; cartridges are clumsy |
| Durability | Knocks and magnets can harm it | No moving parts; resists knocks and magnets | Scratches easily | Must be stored carefully |
| Cost per gigabyte | Low | Highest | Cheap per disc, poor per gigabyte | Lowest of all |
In order of speed, solid state is fastest, then a magnetic HDD, then optical. Magnetic tape is slowest at finding one file because it reads in order from the start, so it suits copying whole archives rather than picking out a single file.
Magnetic and solid state storage hold the most data, while an optical disc holds very little. Hard disks and tape are cheapest per gigabyte and solid state the dearest, so keeping a large amount of data costs least on a hard disk. A disc is cheap to buy, but holding so little makes its cost per gigabyte poor.
Solid state is the most portable and the most durable: it is small, light, unaffected by magnets and has no moving parts for a knock to disturb. An HDD can be damaged by knocks, especially while its disks spin, and a scratch can make part of an optical disc unreadable. Reliability is about longer use: storage that loses data after repeated use, or degrades while stored, is less reliable even if nothing has been dropped.
Worked example: a 2 TB hard disk costing £60 works out at about 3p per gigabyte, while a 1 TB solid state drive costing £120 works out at 12p per gigabyte. The solid state drive is faster and tougher, but each gigabyte costs four times as much.
Practise this
OCR GCSE Computer Science · Storage