CS 1.2.1 Systems Software

22 flashcards · Computer Science · by TheoTyson

1. What is an operating system?

   Manages the operations of the computer, and acts as a bridge between the user and hardwarre. It is held in the secondary storage, but the loader is held in ROM. Copied to RAM when the computer is on.

2. What are the functions of an operating system?

   Memory management. Interrupt service routines. Processor scheduling. Secondary storage management. Input / output device management.

3. What is the function of memory management?

   Data can be shared by more than one program. To stop data being overwritten. Efficient access of programs.

4. What is paging?

   The memory is physically divided into fixed sizes. The program is allocated the pages, but the pages do not have to be contiguous. A page table records the location of the parts of the file. Larger pages means fewer pages, but more waste.

5. What is segmentation?

   Memory is logically divided up into segments of varying lengths that depend on the program structure. Follows the natural breaks in the program, so the parts do not have to be stored continuously.

6. What is virtual memory?

   Secondary storage used as primary memory. When primary memory is full, pages are moved to secondary storage to make space. When needed, the pages are swapped back. Slow process transferring the data. Reduction in computer performance - disk thrashing.

7. What is an interrupt?

   A signal requesting services from the CPU.

8. What happens when the CPU receives an interrupt signal?

   The current process is suspended, and the current registers are stored in a stack. The interrupt service routine (ISR), determines the priorities of tasks to ensure the most important one is serviced. The contents in the stack are retrieved, and execution continues.

9. What is processor scheduling?

   Allocating processor time to each job when only one instruction can be processed at one time.

10. What is round robin scheduling?

    Processes are stored in a first in first out queue, each process is given a quantum (time slice) before the CPU moves on to the next process.

11. What is first come first served scheduling?

    Jobs are processed in the order in which they arrive with no priorities.

12. What is shortest remaining time scheduling?

    The process with the smallest estimated time to completion is run next, requires knowledge of how long jobs will take.

13. What is shortest job first scheduling?

    The process with the smallest estimated running time is run next.

14. What are multi-level feedback queues?

    Multiple queues to store processes to maximise use of the processor and to avoid bottlenecks.

15. What is a distributed operating system?

    A form of parallel processing system spreads the load over multiple computer servers. They are coordinated by the operating system so that it looks like a single system.

16. What is a multitasking operating system?

    A system that can run many jobs simultaneously switching between them so it looks like only one program is running.

17. What is a multiuser operating system?

    Each user gets a slice of processing time so it appears that they are all running at the same time.

18. What is an embedded operating system?

    A system that is used in a computer which serves a specific purpose, but doesn't have much flexibility.

19. What is a real time operating system?

    Systems that needs to process data quickly in order to determine an output, and are not flexible.

20. What is the basic input output system (BIOS)?

    The program that gets the computer started once turned on, it tests the system hardware and loads the operating system into the RAM.

21. What is a driver?

    A program that is a way for hardware to communicate with the operating system.

22. What is a virtual machine?

    When software is able to act as another machine without the specific hardware or operating system.