IGCSE Computer Science 0478 — 3.3 Data Storage Hangman

The 26 key terms

1primary storage

Memory the CPU can access directly, so it is fast. It is made up of RAM (temporary, holds running programs and data) and ROM (permanent, holds start-up instructions).

2volatile memory

Memory that loses its contents when the power is off, like RAM. Non-volatile memory, like ROM and SSDs, keeps its data without power.

3RAM

Random Access Memory: fast, temporary memory that holds the data and programs currently in use. It is volatile, so everything in it is lost when the power is turned off.

4ROM

Read only memory: non-volatile primary storage whose contents are fixed. It keeps the start-up (boot) instructions, so data stays when power is off. Also used in embedded devices.

5RAM vs ROM

RAM is volatile, read/write and holds running programs; ROM is non-volatile, read only and holds start-up instructions. RAM is larger.

6RAM and ROM

ROM holds the start-up instructions that survive power-off. RAM holds the changing operating system, programs and data in use. A computer needs both to start up and to run.

7secondary storage

Non-volatile storage the CPU cannot access directly. It keeps data permanently, even when power is off. Data is copied to RAM before use. Types: magnetic, optical, solid-state.

9platter

A spinning circular disk in magnetic storage. Its surface is split into tracks (concentric circles) and sectors (sections of a track), where data is stored as magnetised areas.

10magnetise

A read/write head uses an electromagnet to magnetise tiny areas of the spinning platter to store 1s and 0s, and reads the data back by detecting the magnetic pattern.

11HDD

Hard disk drive: a magnetic storage device with spinning platters and moving read/write heads. It gives large capacity at low cost, but is slower and more fragile than flash.

12pits and lands

Dents (pits) and flat areas (lands) along a disc's spiral track. A laser reads them by how light reflects: lands reflect it back, pits scatter it. The changes store binary data.

13CD, DVD and Blu-ray

Optical discs read by laser. Capacity rises CD, DVD, Blu-ray as each laser's shorter wavelength packs pits closer. Blu-ray uses blue-violet. Discs are read-only or recordable.

14solid-state storage

Storage that keeps data in flash memory chips with no moving parts. It is non-volatile, so data stays when power is off. Examples are SSD, SD card and USB drive.

15floating gate transistor

A flash memory cell: a transistor with a control gate and a floating gate that traps charge for one bit value and none for the other, so the bit stays stored when power is off.

16NAND and NOR flash

The two ways of arranging flash transistors, named after logic gates. NAND gives high capacity (SSDs, SD cards); NOR gives faster random reads (stored program code).

17SSD, SD card, USB drive

Flash-based solid-state devices: an SSD is the main storage in a laptop, an SD card suits cameras and phones, and a USB drive is a portable stick for carrying files.

18magnetic, optical and solid-state storage

Three types of secondary storage that store data in different ways (magnets, laser pits, flash cells), so they differ in capacity, speed, durability, portability and cost.

19Choosing storage

Match a scenario's needs (capacity, speed, portability, durability, cost) to magnetic, optical or solid-state storage, then justify the choice with reasons.

20virtual memory

Part of secondary storage (HDD or SSD) that the computer uses as extra RAM when real RAM is full. It is slower than RAM.

23paging

Data is split into fixed-size pages. Idle pages are moved out of RAM into virtual memory, then swapped back into RAM when the CPU needs them.

24thrashing

When RAM is full, the computer keeps swapping pages to slow secondary storage, so it becomes sluggish. Adding more RAM reduces swapping. Virtual memory is no replacement for RAM.

25cloud storage

Cloud storage keeps your files on remote servers, owned by another company, that you reach over a network. You can open them from many devices, but you need a connection.

26data centre

A building full of servers and storage devices owned by the cloud provider. It holds users' data, often copied to several locations, and is accessed over the internet.

28cloud storage disadvantages

Problems with saving data online: no internet means no access, ongoing subscription fees, data held by a third party that could be hacked, and slow transfers of large files.

29cloud storage vs local storage

Cloud storage is accessed over the internet from anywhere, but relies on a network and provider. Local storage is on your device: quicker and fully under your control, but less portable.

30point because reason

A full-mark storage answer uses the correct term (e.g. virtual memory, ROM, SSD) and links each point to a reason with 'because', rather than just naming or listing things.