OCR A-Level Computer Science Computer systems (01), June 2025: Question 1

✅ Mark Scheme Answers

• Data bus: Transmits/carries data and instructions between CPU, memory, and hardware components.
• Address bus: Transmits/carries the memory address or location of where data is to be retrieved from or sent to.
• Control bus: Transmits/carries control signals (e.g. read/write, clock, interrupts) to coordinate and synchronise CPU operations.

🧠 Exam Technique & Common Pitfalls

• Key verb: Always mention what is carried and between what components.
• Address Bus trap: Never say the address bus carries "data". It strictly carries addresses / memory locations and is unidirectional.
• Data Bus distinction: Remember the data bus is bidirectional and carries both instructions and operands/data.

✅ Mark Scheme Answers

Input Device (Choose 1):

• Graphics tablet: To sketch, sculpt, or draw game characters and textures.
• Keyboard: To type program code, enter commands, or test game controls.
• Mouse: To select/manipulate 3D models and UI elements in game engines.
• Microphone: To record voiceovers, game character narration, or sound effects.

Output Device (Choose 1):

• Monitor: To view 3D renders, game levels, code, and graphical assets.
• Speakers / Headphones: To hear, mix, and edit audio cues, dialogue, and sound effects.

🧠 Context Matters

• 1 mark for a valid device; 1 mark for its contextual game-design purpose.
• If the device name is placed in the example box, examiners can award forward-transition marks, but keeping them distinct avoids confusion.

✅ Acceptable Answers

Option 1: Solid State Drive (SSD / Flash)

• Reason: Very fast read/write speeds (loads large game assets/HD video files quickly) OR durable/robust with no moving parts.

Option 2: Magnetic (Hard Disk Drive / HDD)

• Reason: Cheaper cost per unit storage / per GB OR high capacity to store massive game/video libraries affordably.

❌ Disallowed Answers

• Optical Storage: CDs/DVDs are explicitly rejected due to very low capacities and slow read/write speeds, making them unfit for large HD videos and modern game editing.
• Mismatched justification: Saying an HDD is chosen because it is "fast" or an SSD because it is "cheap per GB" scores 0 marks for the reason.

✅ Benefits of GPU in Games (Part c-ii)

• Higher frame rates / smoother gameplay: Thousands of stream processors calculate vertex/pixel shaders simultaneously.
• Higher resolutions / HD / 4K / ray tracing: Quickly processes immense pixel grids and lighting transforms.
• Offloads rendering from CPU: Leaves the CPU free to handle game logic, AI, and physics calculations.
• Shorter rendering and loading times: Speeds up asset compilation and scene drawing.

❌ Common Errors in (c)(ii)

• Do not write generic multi-core CPU points (e.g. "it runs multiple programs").
• Must be specific to graphics rendering / visual performance in gameplay.
• Examiner rule: Only mark the first benefit given per answer line. Listing two on one line risks losing marks!

✅ (d)(i) OS Type

Multi-tasking (or Multi-tasking, multi-user).

✅ (d)(ii) Multi-Level Feedback Queue (MLFQ)

• Divides ready processes into different priority queues.
• Each queue has its own priority level and its own scheduling algorithm / time slice (quantum).
• Processes can move between queues based on dynamic behaviour:
  • CPU-bound jobs that exhaust their time slice are demoted to lower-priority queues.
  • I/O-bound jobs or jobs waiting long periods are promoted to higher-priority queues (preventing starvation).
• Balances short interactive tasks with long compute-intensive tasks, reducing I/O bottlenecks.

✅ (d)(iii) Purpose of Device Drivers

• Translates generic operating system I/O instructions into specific hardware-understandable control commands (and vice versa).
• Provides an abstraction layer so the OS and application software do not need to understand specific hardware quirks or register architectures.
• Enables peripheral hardware from diverse manufacturers to interface with a standard OS.

✅ Valid Utilities & Purposes (Choose Any Two)

• Disk Defragmenter: Reorganises fragmented files on an HDD so contiguous file sectors are stored together, reducing drive head movement and boosting read speeds.
• File Compression utility: Uses compression algorithms (lossy/lossless) to reduce asset file sizes, freeing up storage capacity and speeding up file transfers.
• Backup utility: Automates full or incremental copies of game project files to external storage/cloud to protect against data loss.
• Anti-virus / Anti-malware: Scans, detects, and removes malicious code or spyware to safeguard game project integrity.
• Disk Clean-up / System Cleaner: Identifies and deletes temporary files, caches, and redundant setup files to free disk space.
• Encryption software: Scrambles sensitive code or intellectual property using an encryption key so unauthorised parties cannot read it.

🧠 Exam Technique & Pitfalls

• Name + Function pairing: Naming a utility without an accurate technical description of its operation gets 1 mark max.
• Defragmentation clarity: Be specific: say "rearranges parts of files into contiguous storage blocks" rather than just "cleans the drive".
• Utility vs OS vs Application: Make sure you name true utilities. Word processors or IDEs are application software, not utilities.