Mass Storage Media: Magnetic, Optical and Flash

Topic: Y3 Three mass storage media: identify, classify, discuss

The three kinds of mass storage media, explained step by step so you can identify, classify and discuss them: how magnetic, optical and flash storage work, examples of each, and how to compare them by capacity, speed and cost.

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Your phone can hold thousands of photos, a laptop hundreds of films, and a bank's servers the records of millions of customers. That data must survive when the power goes off, which RAM cannot do. It lives on mass storage: devices that keep large amounts of data permanently. This note helps you identify the three kinds, classify devices into them, and discuss their strengths and weaknesses.

SUMMARIZED NOTES

Year 1: Storage devices: capacity, speed and cost, and the three types of storage media (magnetic, optical and flash) with examples of each.
Year 2: No new content on storage media. Year 2 compares RAM with permanent storage (see 'Functions of the main memory').

Year 1 · Magnetic, optical and flash storage

Storage devices store and retrieve data, programs and files for the long term, so users can save, open and manage their work. When comparing them, think about three things. Capacity is how much they hold, usually in gigabytes (GB) or terabytes (TB). Speed covers read and write speeds, access times and data transfer rates. Cost is how much you pay for each unit of storage. All storage media fall into three groups, depending on how they record the 0s and 1s.

Magnetic storage

If you've played with a magnet and iron filings, you know magnets can arrange tiny particles into patterns. Magnetic storage uses a surface coated with a magnetisable material, and patterns of magnetisation represent the binary 1s and 0s. Magnetic storage usually offers high capacity at low cost.

The hard disk drive (HDD) is the most common magnetic device. Inside are spinning disks called platters, and read/write heads that move across them to read and change data, a bit like a record player's arm. HDDs typically hold from several hundred GB to several TB. Magnetic tape stores huge amounts cheaply and is sometimes used to backup server computers, but data must be read in order along the tape, so it is slow to reach.

Optical storage

Hold a CD to the light and you see a rainbow shimmer from its surface. That surface holds tiny pits and flat areas called lands. Optical drives shine a laser onto the disc and examine the reflection to tell pits (1s) from lands (0s). CDs and DVDs are optical discs, used for storing data, installing software, playing media and making backups. They are gradually being phased out in favour of faster, more flexible options.

Flash storage

Flash storage has no moving parts. It uses a special type of memory that can be rewritten and keeps its data when the power is off. It is found in:

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