Chapter 1 - The Function of Operating Systems

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1 Computing - F453 Flashcards on Chapter 1 - The Function of Operating Systems, created by Jamie_472 on 06/10/2013.

Created by Jamie_472 over 6 years ago
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3.1 - The Function of Operating Systems
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Question Answer
What is an interrupt? A message sent to the processor to obtain processor time
What is an example of an I/O interrupt? E.g. Printer is out of paper
What is an example of a timer interrupt? A countdown timer that makes something happen when the countdown ends
What is an example of a hardware error interrupt? E.g. Power failure
What is an example of a program interrupt? E.g. trying to divide by 0
What is an example of a program interrupt? E.g. trying to divide by 0
When is a queue checked? At the end of each CPU cycle
What kind of data structure does a stack have? Last-in-first-out (LIFO)
What is the purpose of scheduling? To arrange jobs that need to be done into an appropriate order
What does it mean when a process is I/O bound? The process makes very little use of the processor and focuses more on input and output
What does it mean when a process is processor bound? The process makes heavy use of the processor to carry out calculations and very little (if any) input or output
What are the three scheduler states? Ready to start, running and blocked
What does the High Level Scheduler (HLS) do? Places jobs entering the system into the ready queue and makes sure that the system is not overloaded
What does the Medium Level Scheduler (MLS) do? Swaps jobs between the main memory and the backing store (e.g. hard drive)
What does the Low Level Scheduler (LLS) do? Moves jobs in and out of the ready state and decides the order in which jobs are to be placed in the running state
What is the purpose of a pre-emptive scheduler? Stops jobs that are currently running to make way for another job
What is the purpose of a non-pre-emptive scheduler? Leaves a job in the running state until it is finished, making other jobs wait
What happens when using the 'First come, first served' scheduling algorithm? The first job to enter the ready queue is the first to enter the running state
What happens when using the 'Shortest job first' scheduling algorithm? The queue is sorted by expected execution time
What happens when using the 'Round Robin' scheduling algorithm? Each job gets a time slice of processing
What happens when using the 'Shortest remaining time' scheduling algorithm? Similar to 'Shortest job first' but jobs move further up the the queue as they are processed
What happens when using the 'Multi-level feedback queues' scheduling algorithm? Involves several queues with jobs moving downwards as they use more processing time. A round robin system is used at the lowest level
What is disk thrashing? Pages swapping in and out and then accessed quickly, causing frequent faults
What is the difference between paging and segmentation? When using paging, pages are equally sized blocks and there is an index to keep track of what is on each page. Pages are stored on a page file. When using segmentation, segments are adjustable sized blocks and each segment holds an entire section of code. They are also indexed. Space is not wasted when using segmentation whereas it can be when using paging
What is spooling? The process of placing data in a temporary working area while waiting for another process to finish
What is the purpose of spooling? To allow the processor to do something else rather than waiting for a peripheral (e.g. a printer) to finish what it is doing as these devices are often very slow
What happens during a Power-on-self-test (POST)? 1) BIOS chip checked and CMOS RAM tested 2) CPU registers verified and cleared 3) Hardware is checked 4) Address of the first instruction of the boot program is loaded into the program counter (PC)
What is a File Allocation Table (FAT)? A computer file system architecture which are commonly found on devices such as floppy disks and flash drives
What is a 'Linked list' used for? To point to the blocks on the disk that contain files