OCR A-Level Computer Science: Software & Systems
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
One of the operating system's central jobs is to share the CPU and main memory fairly among competing processes, and to respond to urgent events using interrupts.
(a) Explain how an operating system manages main memory. Your answer should describe paging, segmentation and virtual memory, including how pages are swapped between RAM and secondary storage. [6 marks]
(b) Explain the purpose of CPU scheduling, and compare round robin with shortest job first (SJF), giving one advantage of each. [4 marks]
(c) State what an interrupt is and describe the role of the interrupt service routine (ISR). [2 marks]
The following scenario was written for this exercise.
A two-person start-up is building its first product: a mobile app for sharing and reviewing local hiking routes. The founders are not yet sure exactly what users will want — they expect the features to change as they get feedback from early users, and they want to release something usable quickly to test the idea in the market. They are deciding whether to develop the app using an Agile methodology or the traditional Waterfall methodology.
Evaluate the use of an Agile methodology rather than the Waterfall methodology for this project. [9 marks]
A high-level program is converted into machine code by a compiler, which works through several stages of compilation.
Describe the four main stages of compilation — lexical analysis, syntax analysis, semantic analysis / code generation and optimisation — stating what each stage does. [6 marks]
Operating systems are specialised for the device and task they run on. Four types are real-time, embedded, distributed and multi-tasking.
For each of the four scenarios below, name the most appropriate type of operating system from that list and justify your choice in one line.
| Scenario | |
|---|---|
| A | A car's airbag controller, which must deploy within a few milliseconds of a crash being detected. |
| B | A simple digital washing-machine controller running fixed software on a low-power chip. |
| C | A search engine whose work is shared across thousands of networked servers acting as one system. |
| D | A laptop running a browser, a music player and a word processor that all appear to run at once. |
[5 marks]
After compilation, a program is combined with pre-written code and prepared to run, using a linker and a loader.
(a) State what a linker does and what a loader does. [2 marks]
(b) Explain the difference between static linking and dynamic linking, and give one advantage of dynamic linking. [2 marks]
When a computer is switched on it goes through a boot process before the operating system is ready, and once running it relies on device drivers to use its hardware.
(a) Explain the role of the BIOS, including what is meant by bootstrapping. [2 marks]
(b) State the purpose of a device driver. [1 mark]