1.2.1 Systems Software Flashcards
1
Q
What is an operating system and its uses?
A
- Acts as a platform for other software to run.
- Uses include:
- Memory management
- Scheduling
- File management
- Input / output
- Device drivers
- User interfaces
2
Q
What is paging?
A
- Logical address space is divided into memory units called pages.
- When a page is loaded into main memory, it is stored in a page frame which are all a fixed size.
- This allows data to be allocated in a non-contiguous manner.
- A page table is used to keep track of which page frames belong to which pages.
3
Q
What is segmentation?
A
- Segments are dynamically sized sections of memory which are allocated to applications when needed.
- OS tracks allocation of memory of each process in a segment table.
4
Q
Definition of an interrupt
A
- An interrupt is a signal that is sent to the processor to request immediate attention.
5
Q
How are interrupts handled by the Interrupt Service Routine (ISR)?
A
- CPU receives interrupt.
- Processor finishes the cycle for the current instruction.
- Current contents of registers are saved to main memory.
- All lower priority interrupts are put on hold to allow the ISR to finish running.
- Program counter is updated with the first address of the ISR.
- Interrupt is executed.
- Contents of the previous instruction are loaded back into registers from memory.
6
Q
How does Round Robin scheduling work?
A
- Time is divided equally among tasks.
- Each task is allocated the same amount of time, if the task isn’t complete by the end of the time slice then the CPU moves on to the next task.
- Isn’t scalable as more programs = smaller time-slice for each application.
7
Q
How does First Come First Served work?
A
- Tasks are executed in the order they are received by the CPU.
- This can lead to starvation which is where tasks are never executed because they are denied CPU time.
8
Q
How Shortest Job First work?
A
- Tasks that take the shortest amount of time to execute are executed first.
- Can lead to starvation.
- Similar to shortest time remaining.
9
Q
How does a Multi-level Feedback Queue work?
A
- Uses a queue of tasks with different priority levels.
- When task is received, it is allocated a priority.
- If it has had too much CPU time it is moved down in priority.
- If a task is idle for too long it moves up in priority.
- This prevents starvation.
10
Q
What is a distributed operating system?
A
- Separate computers are joined together via network connections to work together as a powerful whole.
- Each computer is called a node.
- The distributed OS coordinates the instructions between nodes so that they work together.
- This is used for more complex computing tasks that require more than one CPU.
11
Q
What is an embedded operating system?
A
- Operating system designed for a very specific purpose.
- Operating system is static.
12
Q
What is a multi-user operating system?
A
- Operating system that provides the facilities for multiple users to access the same system without affecting each others settings, data and preferences.
13
Q
What is a real time operating system?
A
- Operating system designed to execute tasks as quickly as possible for real life purposes.
- E.g. self driving cars, plane autopilot.
14
Q
What is the BIOS?
A
- Basic input/output system.
- Initialises and tests the hardware of a computer.
- This is a Power On Self Test (POST)
- BIOS also loads a bootloader (bootstrap) from secondary storage which starts the initialisation of the operating system.
- BIOS is stored on read only flash memory.
- Settings are stored on a CMOS chip which also keeps track of the real time clock.
15
Q
What is the purpose of device drivers?
A
- a device driver provides an interface that allows the operating system to interact with the device, without having to deal with the particular hardware of the device.
- A buffer is often used to prevent data being lost.
