Cambridge 9618 · International A Level Computer Science · ~12 min read
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Categories of Software
Software is broadly divided into two categories:
System software: programs that manage and control the computer's hardware, providing a platform for application software
Application software: programs designed for end users to perform specific tasks (e.g., word processor, browser, game)
Application Software (user-facing programs)
Utility Software (maintenance tools)
Operating System (resource manager)
Hardware
Types of System Software
Cambridge 9618 identifies three main types of system software:
Operating Systems (covered in 1.5.1)
Language translators: compilers, interpreters, assemblers (covered in 1.5.3)
Utility software: programs that perform maintenance and housekeeping tasks on the computer
Utility Software
Utility programs help manage, maintain, and optimise a computer system. They are not essential for the OS to run, but they improve system performance and usability.
Virus Scanner / Anti-malware
Scans files and memory for known malware signatures; quarantines or removes threats. Uses a signature database updated regularly.
Disk Defragmenter
Rearranges fragmented files on a magnetic HDD so their sectors are contiguous, reducing read head movement and improving read speed. Not needed for SSDs.
File Compression
Reduces file size using algorithms (e.g., ZIP). Lossless: original data exactly restored. Lossy: some data discarded (e.g., JPEG images).
Backup Software
Copies data to a secondary location (external drive, cloud) automatically or on schedule. Full, incremental, or differential backups.
Disk Formatter
Prepares a storage device for use by creating a file system structure. Erases all data on the partition.
Encryption Software
Encodes files so only authorised users with the decryption key can read them. Protects data at rest (on storage) or in transit.
Disk Fragmentation
When files are created and deleted repeatedly on an HDD, files become fragmented — their sectors are scattered across the disk. This forces the read head to move to multiple locations to read one file, slowing access.
Defragmentation rearranges these sectors so each file's sectors are physically adjacent (contiguous). This is only needed for magnetic (spinning) HDDs — SSDs have no moving parts, so fragmentation does not affect them in the same way.
File Compression
Compression reduces file size. There are two types:
Type
How it works
Restores original?
Examples
Lossless
Replaces repeated patterns with shorter codes; original data reconstructed exactly
Yes — exactly
ZIP, PNG, FLAC
Lossy
Discards data the human eye/ear is less sensitive to; cannot be reversed
No
JPEG, MP3, MP4
Use cases: Lossless for text, programs, databases (cannot afford any data loss). Lossy for images, audio, video (small quality loss acceptable for large size reductions).
Backup Types
Type
What is backed up
Time/Space
Restore complexity
Full backup
Every file each time
Slow / large
Simple — restore one backup
Incremental
Only files changed since last backup (any type)
Fast / small
Complex — restore full + all incrementals
Differential
All files changed since last full backup
Medium
Restore full + one differential
Exam tip: Cambridge exam questions regularly ask you to distinguish between lossless and lossy compression, and to explain why defragmentation improves performance for HDDs but is not needed for SSDs. Also know the three backup types and when you'd choose each one.
⚠️ Common Mistakes
Saying defragmentation improves SSD performance — SSDs have no moving parts and access all locations equally fast; defragmentation is only relevant for magnetic HDDs
Confusing lossless and lossy compression — lossless is used when every bit matters (programs, text, databases); lossy when some quality loss is acceptable (images, audio)
Saying virus scanners prevent all malware — scanners detect known signatures; new (zero-day) malware may not be in the database and would not be detected
Thinking backup software is part of the OS — backup utilities are utility software, not the OS itself
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Worksheet — 1.5.2 System and Utility Software
7 questions · instantly marked · Cambridge 9618 standard
Q1Distinguish between system software and application software with one example of each.[4]
✅ Mark scheme
System software manages/controls hardware resources and provides a platform for applications [1]; example: OS, device driver, compiler [1]; Application software performs specific tasks for the end user [1]; example: word processor, browser, game [1].
Q2Explain what fragmentation is and describe how disk defragmentation improves HDD performance.[4]
✅ Mark scheme
Fragmentation occurs when a file's sectors are scattered non-contiguously across the disk [1]; this causes the read head to move to multiple positions to read the file, slowing access [1]; defragmentation rearranges sectors so each file's data is contiguous (physically adjacent) [1]; this reduces read head movement so files can be read faster [1].
Q3Explain why disk defragmentation is not necessary for SSDs.[2]
✅ Mark scheme
SSDs have no moving mechanical parts (no read head) [1]; all memory locations are accessed at the same speed regardless of physical location, so fragmentation does not slow access [1].
Q4Explain the difference between lossless and lossy compression, giving one use case for each.[4]
✅ Mark scheme
Lossless: original data can be reconstructed exactly; no data is lost [1]; use case: text files, programs, databases — any data where exact reproduction is essential [1]; Lossy: data is discarded to achieve greater compression; original cannot be fully recovered [1]; use case: images (JPEG), audio (MP3), video — where small quality loss is acceptable for large size savings [1].
Q5Compare incremental and full backup strategies. State one advantage of each.[4]
✅ Mark scheme
Full backup: backs up every file every time [1]; advantage: simple to restore — only one backup set needed [1]; Incremental backup: backs up only files changed since the last backup [1]; advantage: faster and uses less storage than a full backup [1].
Q6Describe how antivirus (virus scanner) software protects a computer from malware.[3]
✅ Mark scheme
The scanner compares files and memory against a database of known malware signatures [1]; if a match is found, the file is flagged as malicious and may be quarantined or deleted [1]; the signature database must be regularly updated to detect new threats [1].
Q7Give three examples of utility software and for each, state what it does.[6]
✅ Mark scheme
Award 1 mark per correct example + 1 mark per correct description (max 6): Virus scanner — scans files for malware, quarantines threats; Disk defragmenter — reorganises fragmented files on HDD to improve read speed; File compression software — reduces file sizes using lossless/lossy algorithms; Backup software — copies data to secondary storage for recovery; Disk formatter — prepares storage with a file system; Encryption software — encodes files to protect from unauthorised access.
Q8Explain the role of a device driver in an operating system. State two reasons why operating system vendors need to release updated device drivers when new hardware is released, and explain what would happen if a user installed new hardware with no compatible driver available.[5]
✅ Mark scheme
Device driver: software that allows the OS to communicate with a specific hardware device using standardised commands — 1 mark; reason 1: new hardware uses new protocols/instruction sets that the old driver does not know about — 1 mark; reason 2: new hardware may have different memory-mapped I/O addresses or interrupt numbers — 1 mark; without a driver: OS cannot communicate with the hardware; device will not function or will cause system errors — 1 mark; (additional valid reason or detail) — 1 mark.
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Mini Test — 1.5.2 Utility Software
10 questions · 10 marks · 10 minutes
⏱ 10:00
Section A — Multiple Choice [5 marks]
Q1Which file format uses lossy compression?
Q2Disk defragmentation is needed for:
Q3A full backup:
Q4Which is an example of utility software?
Q5Lossless compression is required for:
Section B — Short Answer [5 marks]
Q6Explain why a virus scanner may fail to detect some malware.
Mark schemeVirus scanners detect malware by comparing files against a database of known signatures [1]; new (zero-day) malware that is not in the signature database will not be detected [1].
Q7State two advantages of incremental backup over full backup.
Mark schemeFaster to perform — only changed files are backed up [1]; uses less storage space than a full backup each time [1].
Q8Explain why fragmentation slows an HDD and how defragmentation helps.
Mark schemeFragmented files have sectors scattered across the disk — the read head must move multiple times to read one file, increasing seek time [1]; defragmentation moves sectors so the file is contiguous, reducing head movement and speeding up reading [1].
Q9Explain why a program file must use lossless compression rather than lossy compression.
Mark schemeProgram files contain machine code — even a single bit change would corrupt the program [1]; lossless compression ensures the original data is reconstructed exactly; lossy compression would modify the data making the program non-functional [1].
Q10Describe what encryption software does and state one reason why it is useful.
Mark schemeEncryption software encodes/scrambles file data using an algorithm and key so that only authorised users with the correct decryption key can read it [1]; useful because even if files are stolen or intercepted, they cannot be read without the key [1].