What is internal fragmentation on a disc?

Internal fragmentation is the wasted space inside the last cluster allocated to a file. A 5 KB file on a disc with 4 KB clusters fills two clusters and wastes 3 KB.

What is external fragmentation of a disc?

External fragmentation happens when a file is stored in clusters scattered across the disc. Free space is also broken into small non-adjacent gaps.

Explain how fragmentation builds up over time.

Files are deleted and leave gaps of many different sizes across the disc. A large new file is then split to fit into whatever gaps remain.

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Data Structures: Arrays, Records and Hash Tables

Topic overview One-dimensional arrays and indexing Two- and three-dimensional arrays Manipulating arrays: insertion, deletion and searching Records and fields Arrays of records and record manipulation Hash tables, hashing and collisions Choosing and justifying a data structure

Stacks, Queues, Linked Lists and Trees

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Boolean Logic and Simplification

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Recursion and Modular Programming

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Sorting Algorithms

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Big O Notation and Algorithm Efficiency

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Validation, Verification and Testing

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Programming Paradigms and Computer Languages

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Software Engineering Tools and Translators

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Computing, Society and the Law

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Computer Architecture, the Processor and Assembly Language

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Input, Output and Secondary Storage

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Data Transmission and Network Performance

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Number Systems and Binary Arithmetic

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Data Types, Characters and Floating Point

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Databases, Normalisation and Entity Modelling

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SQL, Big Data and Distributed Systems

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The Operating System and Its Modes

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Interrupts, Memory Management and Scheduling

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Types of Software System

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Data Security, Cryptography and Attack

Topic overview Online updating and the integrity of shared files Dangers of holding personal data Clerical procedures, access levels, passwords and write protection Cryptography: its purpose, and symmetric and asymmetric keys Hashing, digital signatures and certificates Caesar and Vernam ciphers and comparing cipher strength Biometric technologies and their limitations Threats, damage and contingency planning Malicious software, hacking and penetration testing

Input, Output and Secondary Storage

Disc organisation, fragmentation and defragmentation

3 things to know
Component 2

Overview

Cluster on a disc, internal fragmentation on a disc and external fragmentation of a disc.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How is the surface of a hard disc organised?

Key term

What is a cluster on a disc?

Key term

What is a file allocation table used for?

Questions from this subtopic

Each one with the model answer underneath.

1
How is the surface of a hard disc organised?
Model answer
A hard disc surface is divided into concentric tracks, and each track into sectors. A cylinder is the same track number taken across all the platters.
2
What is a cluster on a disc?
Model answer
A cluster is a group of adjacent sectors treated as one unit of allocation. The operating system allocates whole clusters to a file, never part of one.
3
What is a file allocation table used for?
Model answer
A file allocation table records which clusters belong to which file. The table also marks which clusters are free.
4
What is internal fragmentation on a disc?
Model answer
Internal fragmentation is the wasted space inside the last cluster allocated to a file. A 5 KB file on a disc with 4 KB clusters fills two clusters and wastes 3 KB.
5
What is external fragmentation of a disc?
Model answer
External fragmentation happens when a file is stored in clusters scattered across the disc. Free space is also broken into small non-adjacent gaps.
6
Explain how fragmentation builds up over time.
Model answer
Files are deleted and leave gaps of many different sizes across the disc. A large new file is then split to fit into whatever gaps remain.

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Boolean Logic and Simplification

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