Flashcards
FMJC.C1
Cards in this deck (19)
- 1Explain why interrupts are used in a computer system?-To obtain processor time
...for a higher priority task
-To avoid delays
-To avoid data loss
-Asynchronous signal to processor
.....that a device needs to be services - 2State two sources of interrupts and explain why these sources have different priorities-Imminent power failure
-Peripheral (e.g. Buffer empty)
-Software failure
-Clock interrupt
-User interrupt (School system)
*Clear reasons* - 3Give one example of an interrupt that allows the job to be resumed after the system has serviced the interruptPeripheral (e.g. Buffer empty)
User Interrupt (New user will log on once previous user's data is saved) - 4Describe how the system ensures that it is possible to resume the interrupted jobValues are copied from registers
....stored on the stack
...so they can be replaced in registers when ISR (Immediate Service Routine) has finished - 5Describe two reasons why scheduling is used?Maximize number of users
...with no apparent delay
Maximize the number of jobs
...as quickly as possible
Efficient processor time/resources
...dependant on priorities
...doesn't monopolise the processor - 6Explain why operating systems use scheduling?Ensure all tasks are processed
...by changing priorities
Processing as many jobs as possible
....in the least possible time
Maximize number of interactive users
...receiving fast response times - 7Describe Round Robin SchedulingEach user allocated a time slice
...when slice ends,moves to next user
Next user uses processor if needs slice
Repeats till all users are serviced
Users may have different priorities
Time slices are small (milliseconds)
No apparent delay for user - 8Describe scheduling methodsFirst Come First Served
Shortest Job First
Round Robin
Shortest Remaining Time
Multi Level Feedback Queue
*easy to explain* - 9Explain why jobs are given different priorities when in a job queueSome jobs are more urgent
Priorities are used to maximize the
use of computer resources
(small jobs can be done and dusted) - 10Reasons why memory management is importantTo deal with allocation when paging & segmentation
To reallocate memory when needed
To protect data and job from each other
Provide security
Shared memory - 11Why virtual memory is needed?To allow programs to run that may need more memory than is available
- 12Describe how virtual memory is usedUse of a backing store as if it was main memory
Uses paging / fixed size units
Swap pages between memory & backing store
Holds part of program that is not needed
Allows programs that need memory to run - 13Describe the problem with disk threshingOccurs when using virtual memory
Constantly swapping pages between memory and disk
Disk is slow
High rate of disk access
More time transferring than processing - 14What ways are segmentation and paging SIMILARBoth are ways of partitioning memory
Used for virtual memory
Both stored in backing store
Assigned to memory when needed - 15What ways are segmentation and paging DIFFERENTSegments are different sizes
Segments are complete programs but pages fit sections of memory
Segments = Logical division
Pages = Physical division - 16One problem when using paging and segmentationDisk threshing
More time is spent swapping pages rather than transferring
The computer may 'hang' - 17Describe spooling & why it's usedSimultaneousPeripheralOperations OnLine
Output data to storage device
...for printing at another time
To allow sharing/network
Job references stored in a buffer/queue
Avoid delays/speed mismatch
...as printers are relatively slow
Jobs can be prioritised - 18State when the BOOT file is used and what is it's purposeWhen
-while the operating system is loading
-when the computer is switched on
-after POST
Purpose
-provide personal settings - 19Purpose of using FAT TableProvides pointers and addresses
Holds file names
Identifies free space
Linked list
Updated when saving or deleting
Stored in IAS
Stores access rights
Maps location of files
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- Flashcards on FMJC.C1, created by FMJC. on 17/06/2015.
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- FMJC.
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