How does a magnetic hard disk drive store data?

Data is stored on spinning platters coated in magnetic material. A read/write head magnetises tiny areas in one of two directions to represent 1s and 0s.

How does optical storage work?

A laser reads a disc by detecting how light reflects from its surface. Changes between pits and flat areas called lands are read as binary.

How does a solid state drive (SSD) store data?

An SSD stores data using electrical circuits and has no moving parts. Electrical charge is trapped in memory cells, so the data stays when the power is off.

AQA GCSE Computer Science 8525

Algorithms

Topic overview Algorithms, decomposition and abstraction Pseudo-code, flowcharts and trace tables Efficiency of algorithms Linear search and binary search Bubble sort and merge sort

Programming

Topic overview Data types Variables, constants and assignment Sequence, selection and iteration Arithmetic, relational and Boolean operators Arrays and records Input, output, string handling and random numbers Subroutines and structured programming Validation, authentication and testing

Data Representation

Topic overview Number bases and why hexadecimal is used Converting between binary, decimal and hexadecimal Units of information: bits, bytes and prefixes Binary addition and binary shifts Character encoding: ASCII and Unicode Pixels, bitmaps and colour depth Bitmap image file size calculations Digital sound: sampling rate and sample resolution Data compression: Huffman coding and run-length encoding

Computer Systems

Topic overview Hardware, software and the operating system Logic gates, truth tables and Boolean expressions Programming languages and translators The CPU and the fetch-execute cycle Types of memory and embedded systems Secondary storage and cloud storage

Computer Networks

Topic overview Network types and topologies Wired and wireless networks Network protocols The TCP/IP model and its layers Network security methods

Cyber Security

Topic overview Cyber security, common threats and penetration testing Social engineering: blagging, phishing and shouldering Malware: viruses, trojans and spyware Methods to detect and prevent cyber security threats

Relational Databases and SQL

Topic overview Relational databases and keys SQL SELECT queries SQL INSERT, UPDATE and DELETE

Ethical, Legal and Environmental Impacts of Digital Technology

Topic overview Ethical issues in digital technology Legal issues, privacy and surveillance Environmental impacts of digital technology

Computer Systems

Secondary storage and cloud storage

3 things to know
Paper 2

Overview

Why secondary storage is needed, how magnetic, optical and solid state drives store data, choosing between them, and the advantages and disadvantages of cloud storage.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is secondary storage?

Key term

Why is secondary storage needed?

Key term

How does main memory differ from secondary storage?

Questions from this subtopic

Each one with the model answer underneath.

1
What is secondary storage?
Model answer
Secondary storage is non-volatile storage that the CPU cannot access directly. Hard disk drives, SSDs and optical discs are examples.
2
Why is secondary storage needed?
Model answer
Main memory loses its contents when the power is off, so files and programs need a permanent home. Secondary storage also holds far more data than RAM.
3
How does main memory differ from secondary storage?
Model answer
The CPU accesses main memory directly, but data in secondary storage must be loaded into RAM first. Secondary storage is slower but larger and cheaper per gigabyte.
4
How does a magnetic hard disk drive store data?
Model answer
Data is stored on spinning platters coated in magnetic material. A read/write head magnetises tiny areas in one of two directions to represent 1s and 0s.
5
How does optical storage work?
Model answer
A laser reads a disc by detecting how light reflects from its surface. Changes between pits and flat areas called lands are read as binary.
6
How does a solid state drive (SSD) store data?
Model answer
An SSD stores data using electrical circuits and has no moving parts. Electrical charge is trapped in memory cells, so the data stays when the power is off.

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Algorithms

Programming

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Computer Systems

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