Pack — 5 System Software (AS Level)

Pack — 5 System Software

Question-and-answer mirror of Jigsaw. Every concept in Jigsaw appears here as a !question with a collapsible !success answer.

How marks are set

• 9618 | — the highest mark tariff that concept has ever carried in a 9618 paper. Answer points = that tariff + 2 spare, newest mark scheme first, older ones filling the gaps.
• 9608 | — same rule, using 9608 tariffs. Still inside the 9618 syllabus wording, but untested in the current series.
• Inferred | — not tested in either series. Tariff estimated from how 9618 marks comparable questions.
• SME | — from the Save My Exams notes. Tariff estimated the same way.

One bullet = one mark, unless the bullet begins … (an expansion of the point above it).

5.2.4 (IDE) is 9618-only and the most examined bullet in the chapter

The 9608 Legend has no IDE questions. 9618 has asked it eleven times since 2021. Every IDE entry below is 9618 | — there is no old-syllabus safety net, and no excuse for leaving it last.

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5.1 Operating Systems

5.1.1 Why a computer system requires an Operating System

Question

Describe the purpose of an Operating System in a computer system.

Answer — 7 points for 5 marks

• Provides a user interface
• … so that the user is able to communicate with the hardware
• Manages memory
• … so that data can be stored and accessed, and multi-tasking is possible
• Manages files
• … allowing the user to create, edit, update and delete files and folders
• Manages inputs and outputs from hardware / peripherals
• Handles processes, making sure each process has fair access to the processor

Latest: 9618_s25_qp_11_sc_6.b

Question

State one purpose of the Operating System.

Answer — 3 points for 1 mark

• To hide the complexities of the hardware from the user
• To provide a platform on which application software can run
• To provide a user interface

Latest: 9618_w23_qp_12_sc_8.a

Question

Explain why a personal computer requires an Operating System.

Answer — 4 points for 2 marks

• Without it the hardware cannot be used // the computer would not function
• It acts as an interface between the user and the hardware
• It provides a platform on which application software can run
• It hides the complexity of the hardware from the user

Latest: 9608_s17_qp_12_sc_4.a.i

Question

Complete the table by identifying the type of software described in each row.

Answer — 6 points for 4 marks

• Manages the hardware and provides a platform for other software → operating system
• Performs a specific housekeeping task on the system → utility program
• Allows the user to carry out a task such as writing a letter → application software
• Converts source code into machine code → translator / compiler
• System software = operating system + utilities + translators
• Application software is not system software, even when supplied with the OS

Latest: 9608_w19_qp_12_sc_1.a

Question

An Operating System provides a user interface. Describe four different types of user interface.

Answer — 6 points for 4 marks

• Command line interface (CLI) — the user types text commands
• … fast for an expert, but the commands must be known exactly
• Graphical user interface (GUI) — windows, icons, menus and pointers (WIMP)
• … intuitive for a novice, but uses more memory and processing power
• Menu interface — the user chooses one option at each stage from successive menus
• Natural language interface (NLI) — the user speaks or types in ordinary language

Inference: “provide a user interface” is credited in both 9618 OS-purpose mark schemes, but no 9618 question has yet asked what the interfaces are. 9618 marks description questions at 1 mark per named item plus expansion, so 4 is the natural tariff.

Question

Explain the problems that would arise if a computer system had no Operating System.

Answer — 5 points for 3 marks

• Every program would have to manage the hardware itself
• … so each program would need its own drivers for every device
• There would be no multi-tasking — only one program could run at a time
• There would be no file system, so data could not be organised or found easily
• There would be no common user interface, so the user must address the hardware directly

Inference: both 9618 questions ask the purpose positively. The inverse framing is a standard 9618 “explain” move, and it marks at 3.

Question

For each of four types of user interface, give one example of a device or system that uses it.

Answer — 6 points for 4 marks

• CLI — MS-DOS, the Linux/Raspbian terminal
• … used by advanced users and system administrators
• GUI — Windows, macOS, Android
• … optimised for mouse and touch input
• Menu — a chip-and-PIN machine, a vending machine, a streaming service
• Natural language — Alexa, Siri, a search engine

SME’s one-line justification for the whole bullet: a user does not need to know where on secondary storage data is kept, only that it is saved for when they want it again.

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5.1.2 Key management tasks carried out by the Operating System

Question

Identify four key management tasks carried out by an Operating System.

Answer — 9 points for 4 marks

• Memory management
• File management
• Security management
• Hardware / device / peripheral / resource management
• Input–output management
• Process management
• Error checking and recovery
• Provision of a platform for software to run on
• Provision of a user interface

Latest: 9618_w25_qp_13_sc_8.d (also 9618_s23_qp_11_sc_3.b, 9618_s21_qp_11_sc_2.b)

Question

Describe the tasks performed by the process management of an Operating System.

Answer — 7 points for 5 marks

• Manages the scheduling of processes // decides which process runs next
• Manages the resources each process requires, such as allocating memory
• Enables processes to share data
• Prevents interference between processes // resolves conflicts between them
• Handles the process queue
• Allows multi-tasking / multi-processing
• … by ensuring fair access, handling priorities and handling interrupts

Latest: 9618_w24_qp_12_sc_3.c (also 9618_s23_qp_12_sc_5.d.i)

Question

Describe the tasks carried out by the file management of an Operating System.

Answer — 6 points for 4 marks

• Allows files to be created, opened, read, written, renamed and deleted
• Organises files into a directory / folder structure
• Keeps track of where each file is physically stored on secondary storage
• … maintaining the file allocation table / directory
• Manages access rights and permissions to files
• Allows files to be moved and copied between locations

Latest: 9618_w24_qp_11_sc_2.b

Question

Describe how the Operating System manages the peripheral devices attached to a computer.

Answer — 6 points for 4 marks

• Installs and uses the appropriate device driver for each peripheral
• Detects devices as they are connected and keeps track of their status
• Sends data to and receives data from each device
• Uses buffers and queues so that slow devices do not hold up the processor
• Handles interrupts raised by devices when they need attention
• Resolves conflicts when two programs request the same device

Latest: 9618_s24_qp_12_sc_4.c

Question

State two tasks performed by the hardware management of an Operating System.

Answer — 4 points for 2 marks

• Communicates with hardware using device drivers
• Allocates hardware resources to the processes that need them
• Keeps track of which devices are connected and available
• Manages the transfer of data between the processor and peripherals

Latest: 9618_w23_qp_11_sc_5.b

Question

State two tasks performed by the security management of an Operating System.

Answer — 4 points for 2 marks

• Manages user accounts, usernames and passwords
• Controls access rights / privileges to files and resources
• Applies updates and patches to the Operating System
• Keeps logs of system access and provides / manages the firewall and anti-malware

Latest: 9618_w23_qp_11_sc_5.c

Question

Describe how the memory management of an Operating System organises and allocates RAM.

Answer — 4 points for 2 marks

• Allocates memory to each program and its data as it is loaded
• Keeps track of which areas of memory are in use and which are free
• Deallocates memory when a process ends, so it can be reused
• Protects each process’s memory so one program cannot overwrite another’s

Latest: 9618_s24_qp_11_sc_3.b

Question

Explain how memory management and process management work together to allow a computer to multi-task.

Answer — 6 points for 4 marks

• Process management schedules the processes, giving each a share of processor time
• … so each appears to run at the same time
• Memory management allocates a separate area of memory to each process
• … so more than one program can be resident in RAM at once
• Memory protection stops one process overwriting another’s data
• When memory is short, virtual memory / paging moves data to backing store so more processes fit

Latest: 9618_w25_qp_12_sc_5.c

Question

Complete the table by writing the name of the management task that matches each description.

Answer — 6 points for 4 marks

• Allocates and deallocates RAM to processes → memory management
• Decides which process the processor runs next → process management
• Keeps track of where files are stored and who may open them → file management
• Communicates with printers and scanners using drivers → device / peripheral management
• Manages usernames, passwords and access rights → security management
• Produces diagnostic messages when something goes wrong → error checking and recovery

Latest: 9618_s22_qp_12_sc_4.a

Question

Describe the tasks carried out by (a) process management and (b) the user interface of an Operating System.

Answer — 8 points, max 4 for each task, 6 marks

• Process management: schedules processes // decides which runs next
• … allocates resources to each process
• … handles interrupts
• … prevents processes interfering with each other
• … enables multi-tasking by sharing processor time
• User interface: allows the user to communicate with the computer
• … hides the complexity of the hardware
• … allows the user to run software and manage files and folders

Latest: 9608_w19_qp_11_sc_2.b

Question

State three tasks carried out by the memory management of an Operating System.

Answer — 6 points for 3 marks

• Allocates memory to programs and data
• Keeps track of which memory is in use and which is free
• Deallocates memory when a process finishes
• Protects one program’s memory from another
• Allocates virtual memory, using paging or segmentation
• Moves data between main memory and backing store

Latest: 9608_w21_qp_11_sc_7.a.i (also 9608_s20_qp_11_sc_8.a at 4 marks)

Question

State two tasks carried out by the input/output device management of an Operating System.

Answer — 7 points for 2 marks

• Sends data to and receives data from peripherals
• Manages device drivers
• Manages buffers and queues for devices
• Handles interrupts raised by devices
• Detects devices as they are connected
• Keeps track of the status of each device
• Handles power management for devices

Latest: 9608_w21_qp_11_sc_7.a.ii (also 9608_s21_qp_13_sc_4.a.i at 3 marks)

Question

State three tasks carried out by the error detection and recovery function of an Operating System.

Answer — 8 points for 3 marks

• Deals with interrupts
• Deals with run-time errors
• Deals with hardware faults
• Produces error diagnostic messages for the user
• Deadlock detection and recovery
• Allows safe-mode boot-up
• Performs a controlled system shutdown
• Maintains and uses restore points

Latest: 9608_s21_qp_13_sc_4.a.ii

Question

State three tasks carried out by the file management of an Operating System.

Answer — 5 points for 3 marks

• Creates, opens, reads, writes, closes and deletes files
• Organises files into folders / directories
• Maintains the directory structure and keeps track of where each file is stored
• Manages access rights to files
• Moves, copies and renames files

Latest: 9608_s18_qp_12_sc_1.a.i

Question

Choose two management tasks carried out by an Operating System. Describe each one.

Answer — max 2 marks per task, 4 marks

• Memory management — allocates memory to each process … and deallocates it when the process ends
• File management — organises files into a directory structure … and controls access rights to them
• Device management — uses drivers to communicate with peripherals … and buffers data so slow devices do not hold up the processor
• Process management — schedules which process runs next … and prevents processes interfering with each other
• Security management — manages accounts and passwords … and applies updates and patches

Latest: 9608_w16_qp_12_sc_7. The candidate picks the tasks — so any two must be worth two marks each, not just nameable.

Question

Describe the sequence of events that takes place when an application program requests a file from the hard disk.

Answer — 10 points for 8 marks

• The application sends a request for the file to the Operating System
• File management looks the file up in the directory / file allocation table
• … and finds its physical address (surface, track, sector)
• It checks the user’s access rights to the file
• Device management issues the read instruction to the disk controller via the device driver
• The read/write head is moved to the correct track and waits for the sector to rotate under it
• The sector is read into a buffer
• An interrupt signals that the transfer is complete
• Memory management allocates an area of main memory for the data
• The data is copied from the buffer into that memory and control returns to the application

Latest: 9608_w16_qp_12_sc_3. The longest single question in this chapter in either series.

Question

Explain how an Operating System uses virtual memory, and describe how paging and segmentation are used.

Answer — 6 points for 4 marks

• When RAM is full, part of the secondary storage is used as though it were RAM
• Pages / segments not currently needed are swapped out to that backing store
• … and swapped back in when they are needed again
• Paging divides memory into fixed-size blocks called pages
• Segmentation divides it into variable-size blocks that follow the program’s logical structure
• Excessive swapping causes disk thrashing, which slows the system down

Inference: 9618 credits “manages virtual memory” inside memory-management answers but has never made it the question. A 4-mark describe is how 9618 handles comparable mechanism questions.

Question

Describe the error checking and recovery tasks carried out by an Operating System.

Answer — 5 points for 3 marks

• Detects run-time errors and hardware faults as they occur
• Produces diagnostic error messages for the user
• Closes the offending process without crashing the whole system
• Detects and recovers from deadlock
• Offers safe mode or a restore point so the system can be recovered

Inference: it appears on the 9618 “identify the key tasks” mark scheme but has never been the subject of its own 9618 question; 9608 asks it at 3 marks, so 3 is the right tariff.

Question

An Operating System must decide which process uses the processor next. Describe how it does this.

Answer — 5 points for 3 marks

• Each process is placed in a queue when it is ready to run
• The scheduler gives each process a slice of processor time in turn
• Processes are given priorities, so more urgent work runs first
• A process is interrupted / pre-empted when its time slice ends or a higher-priority process arrives
• Its state is saved so it can resume from where it stopped

Inference: 9618 credits the word “scheduling” in process-management answers but has not asked the candidate to explain the mechanism.

Question

Describe five key management tasks carried out by an Operating System.

Answer — 7 points for 5 marks

• Memory management — allocates, tracks and deallocates RAM, and manages virtual memory
• File management — organises files and folders and controls who may access them
• Device / peripheral management — uses drivers, buffers and queues to talk to hardware
• Process management — schedules processes and enables multi-tasking
• Security management — accounts, passwords, access rights, updates and logs
• Input/output management — controls the flow of data to and from peripherals
• Error checking and recovery — detects faults and reports or recovers from them

SME frames the chapter around these; the 9618 4-mark “identify” question plus a 1-mark description each gives the tariff.

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5.1.3 The need for typical utility software

Question

Complete the table by writing the name of the utility program that matches each purpose.

Answer — 7 points for 5 marks

• Rearranges files into contiguous blocks to cut access time → disk defragmenter
• Makes a second copy of files so they can be restored → back-up software
• Scans for and removes malicious software → virus checker / anti-malware
• Prepares a disk with tracks, sectors and a file system → disk formatter
• Finds bad sectors and recovers what it can → disk repair / contents analysis
• Reduces file size for storage or transmission → file compression
• Scrambles data so it cannot be read without the key → encryption software

Latest: 9618_w24_qp_13_sc_2.a

Question

Identify one utility program that is not intended to improve the security of a computer, and explain why it is needed.

Answer — 5 points for 3 marks

• Disk defragmenter
• … files become fragmented across the disk as they are edited and deleted
• … it rearranges them into contiguous blocks, so read/access time falls and performance improves
• File compression — reduces file size so less storage is used and transmission is faster
• Disk formatter — prepares a new disk, or wipes an old one, so it can store files

Latest: 9618_s24_qp_13_sc_5.b

Question

Explain how defragmentation software improves the performance of a computer.

Answer — 5 points for 3 marks

• Over time files are stored in non-contiguous blocks scattered across the disk
• … because files are edited, deleted and new files fill the gaps
• The read/write head must move to several places to read one file, which is slow
• Defragmentation rearranges the blocks so each file is stored contiguously
• … so head movement is reduced and access / read time falls

Latest: 9618_w25_qp_11_sc_4.c

Question

Describe the reasons why a computer system needs disk formatting software.

Answer — 5 points for 3 marks

• Organises the disk into tracks and sectors so data can be addressed
• Sets up the file system / directory structure the Operating System will use
• Prepares a new disk so it can be used for the first time
• Erases all existing data from a disk that is being reused or disposed of
• Can identify and mark bad sectors so they are not used

Latest: 9618_s23_qp_13_sc_3.b

Question

Identify two utility programs that can improve the performance of a computer, and state how each does so.

Answer — 6 points for 4 marks

• Disk defragmenter
• … rearranges fragmented files into contiguous blocks, reducing access time
• File compression
• … reduces file sizes, so less storage is used and files transfer faster
• System clean-up / disk clean-up — deletes temporary and unused files, freeing storage
• Virus checker — removes malware that would otherwise consume processor time

Latest: 9618_w24_qp_12_sc_5.b

Question

Explain why a computer system needs back-up software.

Answer — 4 points for 2 marks

• Makes a second copy of the data on a separate medium or in the cloud
• … so the data can be restored if the original is lost, corrupted or deleted
• Protects against hardware failure, theft, fire and ransomware
• Can run automatically on a schedule, so a recent copy always exists

Latest: 9618_s25_qp_12_sc_3.c

Question

Describe the purpose of utility software.

Answer — 4 points for 2 marks

• Performs a specific housekeeping / maintenance task on the computer system
• … keeping the system running efficiently and securely
• It is system software, usually supplied with the Operating System
• Examples: defragmenter, back-up, virus checker, formatter, compression

Latest: 9618_w22_qp_12_sc_1.c

Question

A user’s image files have become corrupted. Identify two utility programs that could help, and state how.

Answer — 4 points for 2 marks

• Back-up software — restores an uncorrupted earlier copy of the files
• Disk repair / contents analysis software — scans for bad sectors and attempts to recover the data
• Virus checker — removes the malware that caused the corruption, preventing further damage
• Disk defragmenter would not help — recognising this is part of the question

Latest: 9618_s22_qp_11_sc_6.c

Question

Identify two utility programs and describe the purpose of each.

Answer — 2 marks per program (name + purpose), 4 marks

• Disk defragmenter — rearranges fragmented files into contiguous blocks to cut access time
• Back-up software — copies files to a separate medium so they can be restored after loss
• Virus checker — scans for, quarantines and removes malicious software
• Disk formatter — organises a disk into tracks and sectors and creates the file system
• File compression — reduces file size for storage or transmission
• System clean-up, firewall, encryption software are also credited

Latest: 9608_w21_qp_11_sc_7.b (also 9608_s21_qp_13_sc_4.b.ii)

Question

Tick to show whether each of the programs listed is a utility program.

Answer — 4 points for 2 marks

• Are utilities: defragmenter, back-up, virus checker, formatter, disk repair, compression
• A translator / compiler is not a utility — it is system software of its own kind
• An IDE is not a utility
• Graphics software and a spreadsheet are application software, not utilities

Latest: 9608_s21_qp_13_sc_4.b.i. The distractors are the whole question.

Question

Explain why a user would use (i) back-up software, (ii) a disk defragmenter, (iii) disk repair software.

Answer — 2 marks per part

• Back-up — a second copy exists … so data can be restored after loss, corruption or hardware failure
• Defragmenter — files are stored in scattered blocks … rearranging them into contiguous blocks cuts read/access time
• Disk repair — scans the disk for bad sectors and corrupted files … marks bad sectors unusable and recovers what it can

Latest: 9608_s21_qp_12_sc_7.a.i–iii

Question

Explain how disk formatting software, disk contents analysis software and disk repair software work together to maintain a hard disk.

Answer — 5 points for 3 marks

• The formatter organises the disk into tracks and sectors and builds the file system
• The contents analysis software scans the disk
• … identifying used, free, bad and corrupted areas
• The repair software then fixes the corrupted files or file system
• … and marks bad sectors so they are not used again, keeping the disk usable

Latest: 9608_s20_qp_12_sc_2.c.i

Question

Describe the purpose of disk repair software.

Answer — 5 points for 3 marks

• Checks the disk for errors and bad sectors
• Attempts to recover data from damaged areas
• Marks bad sectors so that they are not written to again
• Repairs the file system / directory so files can be located
• Reports to the user on the health of the disk

Latest: 9608_w19_qp_12_sc_1.b

Question

Describe the purpose of (a) a virus checker and (b) back-up software.

Answer — max 3 for each, 4 marks

• Virus checker: scans files and memory for known virus signatures
• … and for suspicious behaviour (heuristic checking)
• … quarantines or deletes infected files and alerts the user
• … must be kept up to date with new definitions
• Back-up: makes a copy of files on a schedule or on demand
• … to a separate medium or the cloud
• … so data can be restored after loss, corruption or hardware failure

Latest: 9608_w19_qp_11_sc_2.c

Question

Explain when a virus checker should be run on a computer system.

Answer — 4 points for 2 marks

• Continuously in the background / in real time, as files are opened or downloaded
• On a scheduled full scan of the whole system
• Whenever new external media is connected
• Immediately after the virus definitions are updated

Latest: 9608_w15_qp_13_sc_10.b

Question

Describe how utility software can prevent the accidental loss of data.

Answer — 4 points for 2 marks

• Automatic, scheduled back-ups, so a recent copy always exists
• The copy is kept on a separate device or off-site, so a local failure does not destroy it
• Restore points allow the system to be rolled back to a working state
• Disk repair software recovers files from damaged areas before they are lost

Latest: 9608_s15_qp_12_sc_6.b.i

Question

Describe the purpose of file compression software and explain the difference between its two types.

Answer — 5 points for 3 marks

• Reduces the size of a file so it uses less storage and transmits faster
• Lossless compression removes redundancy and the original can be restored exactly
• … used for text, program files and spreadsheets, where nothing may be lost
• Lossy compression discards data permanently to achieve a smaller file
• … used for images, audio and video, where small losses are acceptable

Inference: compression is named in the 9618 utility mark schemes but has never been the question in this topic; 9618 marks lossless-vs-lossy at 3 elsewhere in the syllabus.

Question

Describe how a virus checker protects a computer system.

Answer — 5 points for 3 marks

• Scans files, memory and incoming data against a database of known virus signatures
• Uses heuristic checking to spot suspicious behaviour from unknown malware
• Quarantines the infected file so it cannot run
• … then deletes or attempts to disinfect it, after alerting the user
• Must be kept up to date, because new malware appears constantly

Inference: 9618 names the virus checker in matching questions but never asks how it works, though 9618 does mark comparable “describe how X protects” questions at 3.

Question

Explain why defragmentation software is not used on a solid-state drive.

Answer — 4 points for 2 marks

• An SSD has no moving parts / no read-write head
• … so access time does not depend on where the data is physically stored
• Defragmentation therefore gives no performance gain
• It also causes unnecessary write cycles, shortening the SSD’s lifespan

Inference: 9618 has examined SSD-vs-HDD structure in Topic 3 and defragmentation here, but has never joined them. It is the obvious synoptic question.

Question

Describe what happens when a hard disk is formatted.

Answer — 5 points for 3 marks

• The disk surface is organised into tracks and sectors
• A file system (e.g. NTFS, FAT32) is written to the disk
• An empty root directory / file allocation table is created
• Any existing data becomes inaccessible // the disk is effectively wiped
• Bad sectors found during formatting are marked so they are not used

SME devotes a section to this; 9618’s own 3-mark formatter question sets the tariff.

Question

Explain why the files on a hard disk become fragmented over time.

Answer — 4 points for 2 marks

• Files are deleted, leaving gaps of free blocks scattered across the disk
• New or edited files are larger than a single gap
• … so the Operating System splits them across several non-contiguous blocks
• The more the disk is used, the more scattered the blocks become

SME explains the cause; 9618’s defragmentation mark scheme credits it as the first point of a 3-mark answer.

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5.1.4 Program libraries

Question

Define the term program library.

Answer — 4 points for 2 marks

• A collection of pre-written, pre-compiled routines / subroutines
• … that perform common tasks
• They are tested and ready to use
• … and can be called by (incorporated into) any program that needs them

Latest: 9618_w25_qp_12_sc_2.a

Question

Explain the benefits to a programmer of using program libraries.

Answer — 5 points for 3 marks

• The routines are already written, so development time is reduced
• They have been thoroughly tested, so they are reliable and contain fewer errors
• The programmer does not need specialist knowledge of that area
• The routines can be reused in many different programs
• They are often optimised, so they run efficiently

Latest: 9618_s25_qp_13_sc_4.b

Question

Describe one benefit of using library routines in a program.

Answer — 1 point + expansion, 2 marks

• The routine is already written and tested
• … so the program is completed faster and contains fewer errors
• or the programmer needs no specialist knowledge … so tasks beyond their expertise can still be included

Latest: 9618_w24_qp_11_sc_5.a.i

Question

Describe one drawback of using library routines in a program.

Answer — 1 point + expansion, 2 marks

• The programmer cannot see or modify the source code
• … so the routine cannot be adapted to fit the problem exactly
• or the routine may contain more code than is needed … so the program is larger and may run more slowly
• or the library must be present when the program runs … so the program will fail if it is missing

Latest: 9618_w24_qp_11_sc_5.a.ii

Question

Describe the benefits to a software company of creating its own program library.

Answer — 5 points for 3 marks

• The routines can be reused across many projects, saving development time
• Code is written and tested once, so quality is consistent
• Maintenance is easier — a fix in the library benefits every program that uses it
• Routines can be shared between programmers in the company
• The library can be sold or licensed to others

Latest: 9618_s24_qp_11_sc_6.c

Question

Explain two benefits of using a Dynamic Link Library (DLL).

Answer — 2 marks per benefit (point + expansion), 4 marks

• The DLL is only loaded into memory when it is needed
• … so the program uses less memory, and the executable file is smaller
• The DLL can be shared by several programs at the same time
• … so the same code is not duplicated on the system
• The DLL can be updated or replaced without recompiling the main program
• … so bug fixes and improvements are distributed easily

Latest: 9618_w25_qp_13_sc_5.b

Question

Describe how a programmer uses a program library when writing a program.

Answer — 4 points for 2 marks

• The library is imported / included at the start of the program
• The programmer calls a routine by its name, passing any required parameters
• … and uses the value the routine returns
• The routine is linked into the program by the linker (at compile time, or at run time for a DLL)

Latest: 9618_s23_qp_11_sc_7.b

Question

State three benefits of using library programs.

Answer — 5 points for 3 marks

• The routines are already written and tested, so development is faster
• They are reliable, because they have been used many times
• The programmer needs no specialist knowledge of that area
• They can be reused in many programs
• They may be optimised, so they run efficiently

Latest: 9608_w21_qp_11_sc_7.c (also 9608_w19_qp_13_sc_6.b at 4, 9608_w16_qp_12_sc_8.a at 4)

Question

State three reasons why a programmer would use DLL files in a program.

Answer — 5 points for 3 marks

• The DLL is only loaded into memory when it is needed, so less memory is used
• The executable file is smaller
• The DLL can be shared by several programs at once
• The DLL can be updated without recompiling the main program
• The source code of the routine stays hidden from the programmer using it

Latest: 9608_s20_qp_13_sc_4.a.i (also 9608_w16_qp_12_sc_8.b.i at 4)

Question

State two reasons why a programmer might choose not to use DLL files.

Answer — 4 points for 2 marks

• The program will not work if the DLL is corrupted
• An external change to the DLL, by another program or a user, could stop the program working
• The DLL must be present at run time — the executable is not self-contained (“unable to find X.dll”)
• A malicious change to a DLL could introduce a virus into the program

Latest: 9608_s20_qp_13_sc_4.a.ii (also 9608_w16_qp_12_sc_8.b.ii at 2)

Question

(i) Describe what is meant by a library routine. (ii) Describe what is meant by a DLL file.

Answer — 2 marks each

• Library routine — a pre-written, pre-tested block of code that performs a common task
• … stored in a library and called by a program when it is needed
• DLL — a file of one or more routines that is not included in the executable at compile time
• … but is linked and loaded at run time, and can be shared between programs

Latest: 9608_s19_qp_11_sc_3.a.ii; 9608_w18_qp_12_sc_6.b.i; 9608_w16_qp_13_sc_2.c

Question

Give one benefit and one drawback of using library routines. Expand each answer.

Answer — 2 marks each (point + expansion), 4 marks

• Benefit: the routine is already written and tested
• … so development time is cut and fewer errors are introduced
• Drawback: the programmer cannot see or change the source code
• … so the routine may do more than is needed, be inefficient, or not fit the problem exactly

Latest: 9608_w18_qp_12_sc_6.b.ii

Question

Explain two drawbacks of using Dynamic Link Libraries in a program.

Answer — 2 marks per drawback, 4 marks

• The executable is not self-contained
• … so the program fails at run time if the DLL is missing, moved or corrupted
• The DLL can be changed by something outside the program
• … so an update by another program, or a malicious replacement, can break it or inject a virus
• Version conflicts arise when two programs need different versions of the same DLL

Inference: 9618 has asked DLL benefits at 4 marks but never the drawbacks. The mirror question at the same tariff is the obvious next step — and 9608 marks the drawback side at 2.

Question

Explain the difference between static linking and dynamic linking of library routines.

Answer — 5 points for 3 marks

• Static linking copies the library code into the executable at compile time
• … so the executable is larger but self-contained and runs without the library present
• Dynamic linking leaves the code in a separate file, linked at run time
• … so the executable is smaller and the library can be shared or updated independently
• … but the DLL must be present and correct whenever the program runs

Inference: 9618’s DLL questions assume the distinction without ever asking for it; a 3-mark compare is how 9618 handles such pairs.

Question

Other than saving development time, state three advantages of using program libraries.

Answer — 5 points for 3 marks

• The routines have been used and debugged by many programmers, so they are dependable
• Complex tasks (graphics, encryption, mathematics) can be used without understanding the theory
• The routine is often optimised for speed or memory by specialists
• Programs written by different people become consistent, because they use the same routines
• The library may be maintained by someone else, so fixes arrive without extra work

SME lists these; 9618’s own 3-mark library-benefit question sets the tariff.

Question

Describe one drawback of storing library routines in DLL files.

Answer — 1 point + expansion, 2 marks

• The program depends on a file it does not contain
• … so if the DLL is deleted, moved, corrupted or replaced with an incompatible version, the program will not run
• The user may see an error such as “unable to find X.dll” and be unable to fix it

SME supplies the content for the untested drawback bullet; 9618’s point-plus-expansion format gives 2.

---

5.2 Language Translators

5.2.1 The need for an assembler, a compiler and an interpreter

Question

Complete the statements describing language translators, using the terms provided.

Answer — 6 points for 4 marks

• An assembler translates assembly language into machine code, one instruction to one machine-code instruction
• A compiler translates the whole high-level program into machine code before it is run
• … producing an executable file that can be run repeatedly without the compiler
• An interpreter translates and executes the program one line at a time
• … and stops at the first error it meets, reporting it to the programmer
• All three convert source code into a form the processor can execute

Latest: 9618_w25_qp_12_sc_6.a

Question

Complete the description of how a compiler and an interpreter translate a program.

Answer — 6 points for 4 marks

• The compiler translates the entire program in one go
• … producing an object / executable file
• … and reports all errors together at the end as an error report
• The interpreter translates one line, executes it, then moves to the next
• … so no executable file is produced
• … and a line inside a loop is re-translated every time it is executed

Latest: 9618_s25_qp_12_sc_5.a

Question

Explain why a programmer would use an interpreter while developing a program and a compiler once it is finished.

Answer — 6 points for 4 marks

• The interpreter stops at the first error and reports it with its line number
• … so errors are found and corrected quickly, without recompiling the whole program
• … and partially written code can be run and tested
• The compiler is used when the program is complete
• … producing an executable that runs faster and needs no translator present
• … and can be distributed without releasing the source code

Latest: 9618_w24_qp_13_sc_6.b

Question

Complete the table by ticking the translator — assembler, compiler or interpreter — that each statement describes.

Answer — 6 points for 4 marks

• Translates assembly language into machine code → assembler
• Translates the whole program before execution → compiler
• Translates and executes one line at a time → interpreter
• Produces an executable file → compiler
• Must be present every time the program runs → interpreter
• Halts at the first error found → interpreter

Latest: 9608_s21_qp_11_sc_8.a.i (also 9608_w17_qp_13_sc_2.a, 9608_s16_qp_12_sc_1)

Question

(i) State the purpose of a language translator. (ii) Name another type of language translator.

Answer — 1 mark each

• Purpose: to convert program code written in one language into another form
• … usually source code into machine code, so the processor can execute it
• Other translators: assembler, compiler, interpreter

Latest: 9608_s19_qp_12_sc_2.a.i and 9608_s19_qp_12_sc_2.a.iii

Question

Describe the purpose of an assembler and explain why it is needed.

Answer — 5 points for 3 marks

• Translates a program written in assembly language into machine code
• Each assembly instruction usually translates to one machine-code instruction (one-to-one)
• It replaces mnemonics with op-codes and labels / symbolic addresses with actual addresses
• The processor can only execute machine code, so the translation is essential
• Assembly language is used where direct hardware control or speed is needed

Inference: 9618 credits “assembler” inside cloze questions but has never asked about it on its own, even though 4.2 examines assembly language heavily. A synoptic 3-mark describe is the natural form.

Question

Explain why a program written in a high-level language must be translated before it can be run.

Answer — 4 points for 2 marks

• The processor can only execute machine code / binary instructions
• High-level source code is written for humans to read, not for the processor
• … so it must be converted into machine code by a compiler or interpreter
• The translation also allows the same source to run on different processors, each with its own translator

Inference: assumed by every question in this sub-topic but never asked directly; 9618 marks such “explain why” questions at 2.

Question

Compare an assembler, a compiler and an interpreter.

Answer — 8 points for 6 marks

• Assembler: translates assembly language, one-to-one, into machine code
• Compiler: translates the whole high-level program at once, producing an executable
• … errors are reported together at the end, as an error report
• … the executable runs faster and without the translator present
• Interpreter: translates and executes a high-level program one line at a time
• … no executable is produced, so the source and the interpreter are needed every run
• … execution is slower, because lines are re-translated each time they are met
• … but errors are reported immediately, one at a time, making debugging easier

SME frames the sub-topic as a three-way comparison; 9618’s 4-mark cloze plus its 2-mark advantage questions justify 6.

---

5.2.2 Benefits and drawbacks of a compiler or interpreter

Question

Describe the advantages of using an interpreter rather than a compiler.

Answer — 6 points for 4 marks

• Errors are reported one at a time, as they are found, with the line number
• … so the error is easy to locate and correct
• The program can be run immediately, with no wait for a full compilation
• Partially written programs can be run and tested
• There is no need to recompile the whole program after every change
• The same source code can run on any machine that has the interpreter

Latest: 9618_s25_qp_12_sc_5.b

Question

State two disadvantages of using a compiler rather than an interpreter.

Answer — 4 points for 2 marks

• The whole program must be compiled before any of it can be run
• Errors are reported only at the end, as a list, so they are harder to locate
• The program must be recompiled after every change, which takes time
• The object code is machine / platform specific

Latest: 9618_w24_qp_12_sc_6.b

Question

A company wants to sell its software to customers. Explain why a compiler is the appropriate translator.

Answer — 5 points for 3 marks

• The compiler produces an executable file
• … which the customer can run without needing a translator installed
• The source code is not distributed, so the company’s work is protected
• The executable runs faster than interpreted code, because it is already in machine code
• The customer cannot alter the program

Latest: 9618_s24_qp_12_sc_6.c

Question

Explain the reasons why a programmer uses a compiler when a program is complete.

Answer — 5 points for 3 marks

• The program is finished and error-free, so line-by-line error reporting is no longer needed
• Compilation produces an executable that can be distributed
• … which runs faster, because it is translated only once
• … and runs without the translator being present
• The source code stays hidden from the user

Latest: 9618_w23_qp_13_sc_5.c

Question

Explain why debugging a program is easier when an interpreter is used.

Answer — 4 points for 2 marks

• The interpreter stops at the first error it meets
• … and reports it together with the line number, so it is easy to find
• Only one error is shown at a time, so the programmer is not overwhelmed
• The corrected program can be re-run immediately, with no recompilation

Latest: 9618_s23_qp_13_sc_6.b

Question

Describe the benefits of using a compiler during the testing of a program.

Answer — 4 points for 2 marks

• The error report lists every error found in one pass
• … so all errors can be corrected together before the next compilation
• The compiled program runs at full speed, so performance can be tested realistically
• It tests the program in the form the customer will receive

Latest: 9618_w22_qp_11_sc_6.c

Question

For the given scenario, identify whether an interpreter or a compiler is more appropriate and justify your choice.

Answer — no mark for the choice; all 3 marks are in the justification

• Still being written / debugged → interpreter: errors reported one at a time with line numbers
• … the program can be run before it is complete, and no recompilation is needed after each change
• Finished / being sold or distributed → compiler: an executable is produced
• … it runs faster, needs no translator on the user’s machine, and hides the source code
• The justification must match the scenario given — generic advantages score nothing

Latest: 9618_w25_qp_11_sc_5.b. Examiners repeatedly note that candidates score the choice and lose the marks.

Question

Explain why a programmer uses an interpreter while writing a program.

Answer — 4 points for 2 marks

• Errors are reported as each line is met, so they are found straight away
• … and the line number is given, so the error is easy to locate
• Sections of an incomplete program can be run and tested
• There is no wait for the whole program to compile after each change

Latest: 9618_s22_qp_13_sc_5.b

Question

Explain why a programmer would use both an interpreter and a compiler when developing software.

Answer — max 3 for each side, 4 marks

• Interpreter — stops at the first error and reports it with its line number
• … errors are easier to find and correct
• … no full recompilation is needed after every change, and partial programs can be run
• Compiler — used once the program is complete, producing an executable
• … which runs faster and without the translator present
• … can be distributed without the source code
• … and can be cross-compiled for a different platform

Latest: 9608_w18_qp_12_sc_6.c. The cross-compilation point is unique to this mark scheme.

Question

State three benefits of using an interpreter.

Answer — 5 points for 3 marks

• Errors are reported one at a time, as they are met, with the line number
• The program can be run and tested without waiting for a full compilation
• Partially written programs can be run
• It is easier to trace and debug the program
• The same source can run on any machine that has that interpreter

Latest: 9608_w21_qp_11_sc_10.a

Question

State one drawback of using an interpreter.

Answer — 4 points for 1 mark

• The source code is needed every time the program runs
• No executable file is produced
• The translator must be present on any machine that runs the program
• Execution is slower, because each line is translated every time it is met, including on every pass of a loop

Latest: 9608_w21_qp_11_sc_10.b

Question

State three drawbacks of using a compiler.

Answer — 5 points for 3 marks

• The whole program must be compiled before it can be run
• Errors are reported only at the end, as a list, so debugging is slower
• The program must be recompiled after every change
• The object code is machine / platform specific
• Compiling a large program takes time and memory

Latest: 9608_s21_qp_13_sc_7.a

Question

Complete the table comparing an interpreter with a compiler.

Answer — 7 points for 5 marks

• Unit translated: one line at a time vs the whole program
• Output: no executable produced vs an executable / object file
• Error reporting: first error, immediately vs all errors at the end
• Translator needed at run time: yes vs no
• Execution speed: slower vs faster
• Re-translation of loops: every pass vs once only
• Source code distributed: yes vs no

Latest: 9608_w15_qp_13_sc_11. The densest single translator question in either series.

Question

Explain why a scripting language such as JavaScript is interpreted rather than compiled.

Answer — 4 points for 2 marks

• The code is sent to the client as source, and must run on any browser or platform
• … so it cannot be pre-compiled into one machine’s machine code
• The browser interprets it as the page loads
• … so it runs immediately, with no separate build step

Latest: 9608_w19_qp_11_sc_2.d

Question

A game is bought as a pre-compiled program. Explain why the user’s computer does not need a translator to run it.

Answer — 4 points for 2 marks

• The program has already been translated into machine code / an executable
• … so the processor can execute it directly
• No translation takes place at run time, so no translator is required
• It also means the source code is not supplied to the user

Latest: 9608_s20_qp_11_sc_8.b

Question

Describe the advantages of using a compiler rather than an interpreter.

Answer — 6 points for 4 marks

• Produces an executable file that can be distributed
• … which runs without the translator being present
• The compiled program runs faster, because it is translated only once
• … a line inside a loop is translated once, not on every pass
• The source code is not distributed, so it is protected from copying or alteration
• Errors are reported all together, so they can be corrected in one pass

Inference: 9618 has repeatedly asked interpreter advantages at 4 marks and compiler disadvantages at 2, but never this direct mirror. Same tariff as its twin.

Question

State three disadvantages of using an interpreter.

Answer — 5 points for 3 marks

• The source code must be supplied every time the program is run
• The interpreter must be installed on every machine that runs it
• Execution is slower than compiled code
• … because each line is re-translated every time it is executed
• No executable is produced, so the program cannot be sold as a stand-alone product

Inference: 9618 asks compiler disadvantages but not interpreter disadvantages; 9608 marks it at 1–3, and 9618’s comparable “state three” questions carry 3.

Question

Explain why a compiled program usually runs faster than the same program run through an interpreter.

Answer — 4 points for 2 marks

• The compiled program is already in machine code, so no translation happens while it runs
• The interpreter must translate each line as it is executed
• … including re-translating lines inside a loop on every pass
• The compiler may also optimise the object code during translation

Inference: 9618 credits “runs faster” as a single point but has never asked why. A 2-mark point-plus-expansion is the standard form.

---

5.2.3 Programs partially compiled and partially interpreted

Question

State a reason why some high-level language programs are partially compiled and partially interpreted.

Answer — 4 points for 2 marks

• The source is compiled into an intermediate code, not machine code
• … which is then interpreted by a virtual machine on the target computer
• This makes the program platform independent — the same intermediate code runs anywhere
• … while still running faster than interpreting the original source directly

Latest: 9618_w25_qp_12_sc_6.c

Question

Describe how a program that is partially compiled and partially interpreted is translated and executed.

Answer — 6 points for 4 marks

• The source code is compiled into an intermediate / byte code
• … this happens once, on the developer’s machine
• The intermediate code is not machine code, so the processor cannot execute it directly
• It is distributed to users and interpreted at run time by a virtual machine
• Each platform has its own virtual machine, so the same file runs on any of them
• Much of the translation work is already done, so it runs faster than pure interpretation

Inference: 9618 asks only for a reason at 2 marks; the mechanism itself has not been asked, and 9618 marks comparable mechanism questions at 4.

Question

Java programs are partially compiled and partially interpreted. Explain how this allows a Java program to run on different computers.

Answer — 5 points for 3 marks

• The Java source is compiled into bytecode
• The bytecode is the same whatever computer will run it
• Each platform has a Java Virtual Machine (JVM)
• The JVM interprets the bytecode into that machine’s own machine code
• … so the program is written once and runs anywhere, with no recompilation

Inference: 9618 has never named a language in this bullet, but the syllabus wording invites it and 9618 routinely sets a named-scenario version of an abstract bullet at 3 marks.

Question

State two drawbacks of a program that is partially compiled and partially interpreted.

Answer — 4 points for 2 marks

• The virtual machine must be installed on every computer that runs the program
• Execution is slower than fully compiled code, because the bytecode is still interpreted
• It uses more memory, since the virtual machine runs alongside the program
• The bytecode can be decompiled more easily than machine code

Inference: 9618 has asked only for the benefit. The drawback mirror is the standard follow-up, at 2 marks.

---

5.2.4 Features found in a typical Integrated Development Environment (IDE)

Question

For each of three purposes — writing code, presenting code and debugging code — identify one feature of a typical IDE and describe it.

Answer — 2 marks per feature (name + description), 6 marks

• Coding / context-sensitive prompts — as the programmer types, the IDE suggests keywords, variable names and parameters
• Dynamic syntax check — the IDE checks each line as it is typed and highlights errors immediately
• Prettyprint / presentation — keywords, variables, strings and comments are shown in different colours and fonts, and code is automatically indented
• Expand and collapse — blocks of code can be hidden so the overall structure is visible
• Single stepping — the program is run one line at a time so the programmer can watch what happens
• Breakpoints — execution stops at a chosen line so the program’s state can be examined
• Variable / watch window — shows the current value of each variable as the program runs
• Report window — lists the errors found, with their line numbers

Latest: 9618_w25_qp_13_sc_6.a

Question

Describe how a programmer uses the debugging features of a typical IDE.

Answer — 6 points for 4 marks

• Single stepping runs the program one line at a time
• … so the programmer can see exactly where the behaviour goes wrong
• Breakpoints stop execution at a chosen line
• … so the program’s state at that point can be examined without stepping through everything
• A variable / watch window shows the current value of each variable as the program runs
• The report window lists errors with their line numbers so they can be located and corrected

Latest: 9618_s25_qp_11_sc_5.c

Question

Describe two named features of a typical Integrated Development Environment.

Answer — 2 marks per feature, 4 marks

• Context-sensitive prompt — offers suggestions as the programmer types … reducing typing errors and the need to memorise syntax
• Dynamic syntax check — checks the line as it is entered … so syntax errors are flagged immediately rather than at compilation
• Prettyprint — colours and indents the code … making its structure easier to read
• Breakpoint — halts execution at a chosen line … so the values of variables can be inspected at that point

Latest: 9618_w24_qp_12_sc_4.b

Question

Complete the table by describing each feature of a typical IDE.

Answer — 6 points for 4 marks

• Single stepping → executes the program one line at a time
• Breakpoint → stops the program at a chosen line
• Variable window → displays the current value of variables during execution
• Report window → lists the errors found, with line numbers
• Expand / collapse → hides or reveals blocks of code
• Auto-indent / prettyprint → formats and colours the code to show structure

Latest: 9618_s24_qp_13_sc_6.a

Question

Other than the one given, identify and describe one presentation feature of a typical IDE.

Answer — name + description, 2 marks

• Colour coding / syntax highlighting — keywords, strings, comments and variables are shown in different colours so they can be told apart at a glance
• Automatic indentation — the IDE indents each block so the program’s structure is visible
• Expand and collapse — sections of code can be hidden to show the overall structure
• Line numbering — every line is numbered so errors can be located from the report window

Latest: 9618_w23_qp_12_sc_5.b.ii

Question

Other than the one given, identify and describe one debugging feature of a typical IDE.

Answer — name + description, 2 marks

• Breakpoint — execution halts at a chosen line so the state of the program can be examined
• Single stepping — the program is run one line at a time so the effect of each line can be seen
• Variable / watch window — shows the value of each variable as the program runs
• Report / error window — lists the errors found together with their line numbers

Latest: 9618_w23_qp_12_sc_5.b.i

Question

Identify two presentation features found in a typical IDE.

Answer — 4 points for 2 marks

• Prettyprint / syntax colour coding
• Automatic indentation
• Expand and collapse of code blocks
• Line numbering

Latest: 9618_s23_qp_12_sc_6.a.i

Question

Identify two debugging features found in a typical IDE.

Answer — 4 points for 2 marks

• Single stepping
• Breakpoints
• Variable / watch window
• Report window listing errors

Latest: 9618_s23_qp_12_sc_6.a.ii

Question

Identify three features of a typical IDE that support the writing of program code.

Answer — 5 points for 3 marks

• Context-sensitive prompts / auto-complete
• Dynamic syntax checking as the code is typed
• Initial error detection, flagging mistakes before compilation
• A built-in editor with line numbering and auto-indent
• Built-in translators, so code can be compiled or run from within the IDE

Latest: 9618_w22_qp_13_sc_6.a

Question

Explain how the dynamic syntax checking feature of an IDE helps a programmer.

Answer — 5 points for 3 marks

• Each line is checked as it is typed, not when the program is compiled
• Errors are highlighted immediately, usually by underlining the offending text
• … so the programmer corrects them while the line is still fresh in mind
• Fewer syntax errors reach compilation, so the error report is shorter
• It reduces the time spent on repeated compile-and-fix cycles

Inference: named in the syllabus and credited inside table answers, but never the subject of its own 9618 question; comparable “explain how this feature helps” questions carry 3.

Question

Describe how the translators built into an IDE support a programmer.

Answer — 4 points for 2 marks

• The IDE contains both an interpreter and a compiler
• The interpreter lets the programmer run and test code while it is still being written
• The compiler produces the executable once the program is complete
• … so the programmer never has to leave the IDE to translate the program

Inference: the syllabus lists built-in translators among IDE features, and it is credited in the 3-mark “writing tools” mark scheme, but no question has targeted it.

Question

Explain why a programmer would use an Integrated Development Environment rather than a simple text editor.

Answer — 5 points for 3 marks

• All the tools needed — editor, translator and debugger — are in one program
• Errors are caught as the code is typed, so fewer reach compilation
• Prettyprint and indentation make the code easier to read and maintain
• Debugging tools such as breakpoints and the variable window make faults easier to find
• The overall effect is faster development with fewer errors

Inference: every 9618 question asks for features; none asks for the rationale. A 3-mark “explain why” is the obvious untested angle on the chapter’s most examined bullet.

Question

State the features of a typical IDE under the headings: coding, initial error detection, presentation and debugging.

Answer — 8 points for 6 marks

• Coding — context-sensitive prompts / auto-complete
• … built-in editor with line numbering, auto-indent and auto-correct
• Initial error detection — dynamic syntax checks as each line is typed
• … errors highlighted or underlined before compilation
• Presentation — prettyprint: colour coding of keywords, strings and comments
• … expand and collapse of code blocks to show structure
• Debugging — single stepping, breakpoints
• … variable / watch window and a report window listing errors with line numbers

These four headings are the syllabus’s own; SME organises the notes this way and 9618’s 6-mark IDE question is the largest tariff in the chapter.