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A-Level Computer Science > 4: Operating Systems > Flashcards

4: Operating Systems Flashcards

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1
Q

What are the 5 types of scheduling algorithm?

A
  • RR (Round Robin)
  • SRT (Shortest Remaining Time)
  • MFQ (Multi-level Feedback Queue
  • FCFS (First Come First Served)
  • SJF (Shortest Job First)
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2
Q

Which of the scheduling algorithms are pre-emptive?

A
  • RR
  • SRT
  • MFQ
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3
Q

Which of the scheduling algorithms are non pre-emptive?

A
  • FCFS
  • SJF
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4
Q

How does RR (Round Robin) work?

A

Each process is given a maximum length processor time in the running state after which it is put back into the ready queue

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5
Q

How does SRT (Shortest Remaining Time) work?

A

The ready queue is sorted on the estimated time to complete the process. Processes that arrive having a shorter time to complete than the current running process are moved to the running state

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6
Q

How does MLFQ (Multi-level Feedback Queue) work?

A

Several ready queues are used each with a different scheduling algorithm. Jobs are able to move between queues as their priorities change

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7
Q

How does FCFS (First Come First Serve) work?

A

The first job to enter the ready queue is the first to enter the running state

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8
Q

How does SJF (Shortest Job First) work?

A

Jobs are sorted in the ready queue according to the estimated processor time needed and are ran until they are finished

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9
Q

What is a device driver?

A

Software that tells the operating system how to communicate with a device

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10
Q

What is a virtual machine?

A

A program that has the same functionality as a physical computer

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11
Q

What is segmentation?

A

the division of complete sections of programs into logical divisions of different sizes to allow it fit into main memory

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12
Q

How does the operating system perform multi-tasking?

A
  • The processor allocates a small amount of time to each process and cycles between them
  • As this happens so quickly, it appears as if multiple programs are executing simultaneously
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13
Q

How does the operating system help with file management?

A
  • An extension to the file name tells the operating system which application to load the file into
  • An operating system may present a logical structure of files in folders and allow the user to rename, delete, copy and move files
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14
Q

How does the operating system deal with user management?

A
  • The operating will allow multiple users to log into the same computer by retaining settings for each user such as icons, desktop backgrounds etc
  • each user may have different access rights to files and programs
  • A client-server network may impose a fixed or roaming profile for a user and manage login requests to the network
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15
Q

How does the operating system deal with a user interface

A
  • uses a WIMP interface (windows, icons, menus and pointers)
  • WIMP is interactive, visual, intuitive and optimised for mouse and touch gesture input
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16
Q

What is paging?

A
  • Physical divisions of programs that are fixed in size
  • paging takes no account of how it splits the program, only that it splits it into fixed-sized pages made to fit sections of memory
17
Q

What is virtual memory?

A
  • If physical memory is running low, virtual memory must be used
  • Applications stored in RAM that haven’t been used in a while are transferred to memory on the hard disk (virtual memory) in order to free up space in RAM for other applications
  • If those applicationd are needed again, they are sent out of virtual memory and back into RAM and another application is swapped in its place
  • if more time is spent moving pages/segments from memory to the disk (thrashing) than processing instructions, the computer will be very slow
18
Q

What is an interrupt?

A

Signal from hardware or software indicating that an event has occurred or that a process needs attention.

19
Q

What is an interrupt service routine?

A

The software with a set of instructions that halt the execution of the CPUs current program to allow for the operations of the interrupt to be carried out

20
Q

When the interrupt is complete, how will the processor know to continue the previously executed program?

A
  • When an interrupt is received, the values held in the registers are copied into a data structure in the memory known as the stack
  • These values are pushed onto the stack in a stack frame, effectively saving them for later retrieval
  • The interrupt can now be executed
  • Once the interrupt is complete, the frame is then popped off the top of the stack, allowing for the retrieval of the previous values for the original program, which can then be loaded back into the processor registers and executed
21
Q

Examples of hardware interrupts

A
  • Power supply failure
  • Power/reset button pressed
  • Power-down command
22
Q

Examples of user interrupts

A
  • Moving the mouse
  • Clicking/tapping an icon to open a new program
  • Keyboard presses
23
Q

Examples of software interrupts

A
  • Illegal instruction encountered
  • Arithmetic overflow
  • New log-on request
24
Q

Examples of interrupts on input/output devices

A
  • Buffer nearly empty
  • Signal the completion of a data transfer to/from a device
  • Printer ink supply notification
25
Q

How does a multi-tasking operating system work?

A

Each active program is scheduled to receive a tiny time slice in quick rotation, giving the impression they are operating at the same time

26
Q

How do multi-user operating systems work?

A
  • The computer manage the user’s various permissions and access rights when they log on
  • Server operating system software will handle the requests of multiple people using different computers on a network at the same time
27
Q

how does a distributed operating system work?

A
  • you can combine the processing power of multiple computers across a network for a single task
  • the operating system controls and coordinates the computers, presenting them to the user as if they were a single system
28
Q

how do embedded operating systems work?

A
  • they tend to run on dedicated hardware so they run with maximum efficiency, using low-powered processors and very little memory
  • examples include washing machines, home assistants, traffic lights
29
Q

How does real-time operating systems work?

A

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A-Level Computer Science (25 decks)

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