Systems Software

What Systems Software covers

Systems Software is examined on component 01 of OCR Computer Science, Computer systems. 97 recall questions across 7 subtopics.

The 7 subtopics

Each one has its own page.

• Operating systems: need, function and purposeRecall questions on what an operating system is and why one is needed, its functions including user interfaces, resource, file and security management, the kernel, kernel and user mode, and system versus application software.Open →
• Memory management: paging, segmentation and virtual memoryRecall questions on memory management, paging, segmentation and virtual memory, page tables, page faults, disk thrashing, calculating frames and wasted space, external fragmentation, combining paging with segmentation, and memory protection.Open →
• Interrupts and the interrupt service routineRecall questions on interrupts and why they beat polling, the interrupt service routine, when the interrupt register is checked, saving registers on a stack, the interrupt vector table, priorities, hardware and software interrupts, and scheduling.Open →
• Scheduling algorithms: first come first served, round robin and shortest job firstRecall questions on why an operating system schedules processes, pre-emptive and non-pre-emptive scheduling, burst, waiting, turnaround and response time, and how first come first served, round robin and shortest job first work and fail.Open →
• Scheduling algorithms: shortest remaining time, multi-level feedback queues, traces and choosing an algorithmRecall questions on shortest remaining time and multi-level feedback queues, knowing burst times in advance, traces comparing first come first served, shortest job first, shortest remaining time and round robin, starvation, and justifying a scheduling algorithm.Open →
• Types of operating systemRecall questions on distributed, embedded, multi-tasking, multi-user and real time operating systems, why real time is not simply fast, the advantages and drawbacks of each type, and choosing a type for a stated scenario.Open →
• BIOS, device drivers and virtual machinesRecall questions on what the BIOS does at start-up, the power-on self test, device drivers and why they are device and operating system specific, and virtual machines that run intermediate code or host a guest operating system.Open →

What you need to know

Answer each one before you reveal it.

Take Systems Software further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Paging vs Segmentation

  Paging: dividing memory into fixed-size blocks, which need not be contiguous. Segmentation: dividing memory into variable-size blocks that follow the logical divisions of a program.

• A hardware interrupt vs A software interrupt

  A hardware interrupt: a signal raised by a device outside the processor to request attention. A software interrupt: a signal raised by a running program, typically to ask the operating system for a service.

• An interrupt service routine vs The interrupt vector table

  An interrupt service routine: the code run to deal with a signal once it has been accepted. The interrupt vector table: the list of addresses telling the processor where the handling code for each signal lives.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is an operating system?

   Model answer

   A collection of system software that manages the computer's hardware and resources and provides an environment in which application software can run. It sits between the user and applications on one side and the hardware on the other, so that programs do not have to control the hardware directly.

2. 2

   Why do we need an operating system at all? Could a program not just talk to the hardware itself?

   Model answer

   It could, but every program would then have to contain its own code for every possible processor, memory layout, disk, keyboard and printer, and two programs running at once would fight over the same hardware. The operating system provides one shared, tested layer that hides hardware differences, shares resources fairly between programs and stops one program corrupting another.

3. 3

   Describe five functions carried out by an operating system.

   Model answer

   Any five of: memory management (deciding where programs and data sit in RAM and moving pages in and out); processor scheduling (deciding which process gets the CPU and for how long); file management (organising storage into a directory structure, handling create, read, write and delete); input and output device management through device drivers; interrupt handling; providing a user interface; security and user account management, including permissions and logging in; providing utilities for maintenance.

4. 4

   What is meant by a 'user interface' as a function of the operating system, and name the two main kinds.

   Model answer

   The means by which a human interacts with the machine. A graphical user interface (GUI) uses windows, icons, menus and a pointer and is easy for a non-expert; a command line interface (CLI) takes typed text commands, which is harder to learn but faster for experienced users, uses fewer resources and can be scripted and automated.

5. 5

   Explain the term 'resource management' in the context of an operating system.

   Model answer

   The operating system controls access to limited resources - processor time, memory, storage, and input and output devices - and allocates them between competing processes. It decides who gets what and when, reclaims resources when a process finishes, and prevents two processes using the same resource in a way that would corrupt data.

6. 6

   How does an operating system provide a 'platform' for application software?

   Model answer

   It exposes a consistent set of services and interfaces (often called an application programming interface) that applications call instead of controlling hardware. A word processor asks the operating system to save a file; it does not need to know whether the storage is a hard disk drive, a solid state drive or a network share.

What is inside Levo

Six ways to work the same material.

Systems Software revision questions

What does Systems Software cover in OCR A-Level Computer Science?

7 subtopics: operating systems: need, function and purpose, memory management: paging, segmentation and virtual memory, interrupts and the interrupt service routine, scheduling algorithms: first come first served, round robin and shortest job first, scheduling algorithms: shortest remaining time, multi-level feedback queues, traces and choosing an algorithm, types of operating system and bios, device drivers and virtual machines. Each one has its own page with questions and model answers.

How is Systems Software organised?

By the OCR H446 specification, subtopic by subtopic, so it matches the order you are taught it in.