3.3 Data storage

By the end of this section you should be able to

• 3.3.1 Describe primary storage, including RAM and ROM
• 3.3.2 Describe secondary storage
• 3.3.3 Explain how magnetic, optical and solid-state storage work
• 3.3.4 Explain virtual memory
• 3.3.5 Compare cloud storage with local storage

Lessons

1. Primary storage: RAM and ROM
2. Secondary storage: HDD and SSD
3. Off-line storage: optical, tape and flash
4. Cloud storage

Key vocabulary

Primary storage

Storage that the CPU accesses directly, such as RAM and ROM.

RAM

Volatile memory holding the data and programs currently in use.

ROM

Non-volatile memory holding instructions that do not change, such as the start-up instructions.

Secondary storage

Non-volatile storage not directly accessed by the CPU, used to keep data long term.

Magnetic storage

Stores data on platters divided into tracks and sectors, read and written by electromagnets.

Optical storage

Uses a laser to create and read pits and lands, e.g. CD, DVD and Blu-ray.

Solid-state storage

Flash memory using NAND or NOR technology with control and floating gates.

Virtual memory

Part of secondary storage used as extra RAM, with pages swapped in and out when needed.

Cloud storage

Data stored on remote physical servers and accessed over the internet.