A-Level Computer Science: Scheduling, Memory Management and Compilation

This material trains the systems software content of A level Computer Science: how an operating system shares the processor and memory between programs, what happens when a computer starts, and how source code becomes a program that runs. It is for Year 12 and Year 13 students who know what an operating system and a compiler are for and need the detail behind them.

The quiz has twelve questions. Four use the same set of four processes, with their arrival and burst times given in the question, and schedule them in four ways: the average waiting time under first come, first served, the completion order under shortest job first without pre-emption, the process that runs between 2 and 3 ms under shortest remaining time with a stated tie rule, and the completion order under round robin with a stated queue rule. Because the data is the same, the student can see how the choice of algorithm changes the result. A fifth asks what a multi-level feedback queue does with a process that uses its whole time slice. Three are about memory and start-up: recognising disk thrashing, the difference between paging and segmentation, and what the BIOS does at power-on. One asks for an example of a virtual machine. The last three follow a program through translation: what lexical analysis does, which stage catches a missing bracket, and the difference between static and dynamic linking.

Every explanation draws the timeline or follows the process step by step and says why the tempting wrong answer does not fit, such as forgetting that a non-pre-emptive job cannot be interrupted.

The flashcards cover the five scheduling algorithms, starvation and ageing, paging, segmentation, virtual memory, thrashing, the BIOS, device drivers, real-time operating systems, the stages of compilation, and linkers and loaders.

The written work has eight longer tasks to answer on paper: a full shortest remaining time schedule with waiting times compared against first come, first served; round robin compared with shortest job first; virtual memory and thrashing; the boot process; the four stages of compilation and their outputs; libraries, linkers, loaders and the two kinds of linking; two uses of virtual machines; and four types of operating system. Each task has a model answer and the points a marker would look for.

There is also a short oral practice with an examiner, who gives all process data and tie rules in full, asks one question at a time and gives brief feedback at the end.

The content is based on the systems software sections of the A level specifications, for example OCR H446 sections 1.2.1 and 1.2.2 (scheduling algorithms, memory management, BIOS, virtual machines, stages of compilation, linkers and loaders) and AQA 7517 sections 4.6.1 to 4.6.3 (the role of the operating system and program translators).

• Trace FCFS, shortest job first, shortest remaining time and round robin schedules and calculate waiting times
• Explain multi-level feedback queues, starvation and ageing
• Explain virtual memory, disk thrashing, paging and segmentation
• Describe the boot process, the BIOS, device drivers and virtual machines
• Describe the stages of compilation and the stage at which an error is found
• Explain the roles of libraries, linkers and loaders and compare static and dynamic linking

Practice material written by Zestly, based on the systems software content of the A level Computer Science specifications (for example OCR H446 sections 1.2.1 and 1.2.2, and AQA 7517 sections 4.6.1 to 4.6.3).