SLR 04 - Operating Systems & System Software Flashcards
What does the OS handle?
User Access / Logging in
Application Software
Memory Management
User Interface
Utility Programs
File Management
Device Drivers
What is Multitasking?
The processor allocating time to several processes when multiple apps are open
What is defragmentation?
When there is space for a program but not contigually, it moves programs to make space for a program to be in RAM
What is Paging?
Pages are of a fixed size
Made up of physical divisions
Programs are split up into a series of pages
Can be inefficient as programs in a loop can be spread in RAM
What is Segmentation?
Segments are different sizes
They are complete sections of programs
Segments are logical divides
What are the similarities between Segments and Pages?
Both run despite insufficient memory
Both are stored on disks
They are transferred onto memory when needed
What are the differences between Segments and Pages?
Pages are fixed sizes, segments are different
Pages fit memory, segments have program sections
Pages are physical, Segments are logical
What is virtual memory?
When physical memory is running low virtual memory is used
If more time is used moving data in memory than processing it, the computer is slowed
When do interrupts occur in the FDE cycle?
After execute
What are interrupts?
A way to signal the processor from other devices during the FDE
What does ISR stand for?
The Interrupt Service Routine
What occurs during the ISR?
The contents of the interrupt register is copied to the program counter for the instruction of the interrupt
Registers contents from before the interrupt are copied into a stack for retrieval
Once the interrupt is complete these are copied back into the registers continuing the program from before the interrupt
What are some examples of interrupts?
Power Down : Hardware
Moving the mouse : User
Arithmetic Overflow : Software
Screen Recording app : Timer
Buffer Empty : Input / Output
What do schedulers allow for?
Effective management of multi-tasking operating systems
What do schedulers manage?
What to process next
The length of time a process can execute for
What are examples of sceduling algorithms?
FCFS - First come first serve
SJF - Shortest job first
RR - Round Robin
SRT - Shortest remaining time
MLFQ - Multi-Level feedback queue
How does FCFS work?
Processes execute in the order they arrive
Processes waiting in queue just wait
How does SJF work?
Picks processes that take the least time and run til completion
Follows same post-execute process as FCFS
How does RR work?
Each process is alocated a time slice
If not completed by the end of this it returns to the back of the ready queue
How does SRT work?
Similar to SJF
Processes are suspended if higher-priority processes join the queue
How does MLFQ work?
Used in multi-processor systems
Can handle multiple process queues at the same time
Scheduler moves jobs between queues as needed
What is a device driver?
It is software that translated code to be understood by another device
What are the types of operating systems?
Distributed
Multi-Tasking
Multi-User
Embedded
Real-Time
What is distributed computing?
When the OS controls and co-ordinated several computers and presents them as 1 system
What is an embedded OS?
It runs on dedicated hardware to maximise efficiency of a system using little memory
What is a real-time OS?
Processes in real-time systems must execute in a certain time frame
Redundancy is built into real-time systems to handle sudden increases in input
Real-time systems rarely run at full capacity
