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CAIE 9618 · Paper 1 · Topic 1.5.2

System & Utility
Software

OS Types · Library Routines · Utilities · Backup · Defrag · Antivirus

CSZone Cambridge International AS & A Level Computer Science 9618
Types of Software

System Software vs Application Software

SYSTEM SOFTWARE
Manages and controls the computer hardware. Runs in the background. Examples: OS, device drivers, utilities, translators. Required for the computer to function.
APPLICATION SOFTWARE
Programs that perform tasks for the user. Run on top of the OS. Examples: word processor, browser, game, spreadsheet. Depend on system software to access hardware.
System software sits between hardware and applications — it provides the services that applications rely on. Without system software, applications cannot run.
Types of Operating System

Different OS for Different Contexts

Multi-user OS — supports multiple users simultaneously (e.g. Linux server, mainframe OS). Each user gets own process space.
Multi-tasking OS — runs multiple processes simultaneously (illusion via scheduling). e.g. Windows, macOS, Linux.
Real-time OS (RTOS) — guarantees response within a specified time. Used in embedded systems (e.g. aircraft, medical devices, car ECUs) where timing is critical.
Distributed OS — coordinates multiple networked computers to appear as one system. Used in cloud computing clusters.
Embedded OS — minimal OS for specific devices (e.g. smartwatch, router, camera).
Library Routines

Reusable Pre-written Code

Library routines are pre-tested, reusable code modules that can be called by any program. Saves programmers from re-writing common functions (e.g. mathematical functions, string handling, network communication).
STATIC LINKING
Library code is copied into the executable at compile time. Larger program file, but self-contained — no external dependencies at runtime.
DYNAMIC LINKING (DLL/so)
Library loaded at runtime from a shared file. Smaller executable. Many programs share one library file. If library updated, all programs benefit automatically.
Utility Software

Tools for Maintaining the System

Antivirus / Anti-malware — scans files for known malware signatures; heuristic analysis for new threats; quarantines/removes infected files
Disk defragmenter — reorganises fragmented files so they are stored in contiguous sectors; reduces read time on HDDs (not needed for SSDs)
Backup utilities — copy files to a second location. Full backup (all files), incremental (changes since last backup), differential (changes since last full backup)
Compression utilities — reduce file size using lossless (ZIP) or lossy (JPEG) methods; save storage and reduce transfer time
Disk cleanup / file manager — removes temporary files, empties recycle bin, frees up disk space
Exam Practice

Cambridge-style questions

Question 1
Explain the difference between an incremental backup and a full backup. State one advantage of each.
4 marks
1 mark
Full backup: copies ALL files regardless of whether they have changed since the last backup
1 mark
Advantage of full backup: simple, fast to restore — only one backup set needed to recover all data
1 mark
Incremental backup: copies only files that have changed since the last backup (full or incremental)
1 mark
Advantage of incremental backup: faster and uses less storage per backup — only changed files are saved
Common Mistakes

Don't lose easy marks

1
Saying defragmentation improves SSD speed — defragmentation benefits HDDs (which have mechanical read heads). SSDs use flash memory with no moving parts; defragmenting an SSD provides no benefit and can reduce its lifespan by causing unnecessary write cycles.
2
Saying antivirus software prevents all malware — antivirus detects and removes known malware using signature databases, but zero-day threats (unknown malware) may not be detected. Heuristic methods help but cannot catch everything.
3
Confusing incremental and differential backup — incremental backs up changes since last backup (any type); differential backs up all changes since the last full backup only. Restoration: incremental needs multiple sets; differential needs just 2 sets (last full + latest differential).
Topic Summary — 1.5.2

What You Need to Know

SOFTWARE TYPES
System software: OS, drivers, utilities, translators
Application software: user-facing tasks
OS TYPES
Multi-user, Multi-tasking, Real-time (RTOS), Distributed, Embedded
LIBRARY ROUTINES
Static linking: copied at compile time
Dynamic: shared at runtime (DLL/so)
UTILITIES
Antivirus: signature + heuristic scanning
Defrag: HDD only (not SSD)
Backup: Full / Incremental / Differential
Compression: lossless/lossy
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1.5.3
Translators
Assembler · Compiler · Interpreter · Comparison
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