system software pmt flashcards
what is an operating system
a collection of programs that work together to provide an interface between the user and the computer
give three functions of an operating system
memory management, resource management,i/output management, interrupt management, security,user interface, utility software
what are the similarities and differences between paging and segmentation?
both are used when RAM space is insufficient , can cause disk thrashing
-Paging:used equal sized called pages
-segmentation:uses variable sized, logical sections called segments
Describe how virtual memory is used when there is not enough RAM
a section of the hard drive is used as RAM ,sections of programs not currently being used are temporarily moved into virtual memory through paging
-this frees up memory for other programs In RAM
What is an interrupt
a signal generated by software or hardware to indicate to the processor that a process needs attention
explain the stages of the interrupt service routine
-interrupt register checked at the end of each fetch decode execute cycle
-if there is an interrupt exists with a higher priority to the current process, the current contents of the registers in the CPU are transferred into a stack
-the relevant interrupt service routine (ISR) is loaded into RAM
-a flag is set to signal the ISR has begun
-The flag is reset once the ISR has finished
-interrupt register checked again If interrupts are a higher priority , the process is repeated
-if there are no interrupts with a higher priority , the contents of the stack are popped and place back into the special memory registers
-the fetch decode execute cycle renews as before
which scheduling algorithms are pre emotive or non preemptive
pre - emotive:RR.STR,MLFQ
non-preemptive:FCFS,SJF
What are the advantage and disadvantage of using multilevel feedback queues for scheduling
advantage:services most urgent interrupts first
disadvantages:hard to implement
define a real time operating system and when it may be used
real time operating systems perform a task within a guaranteed time frame.
They are used in systems were a response within a given time frame is critical eg. life supports
define three functions of the BIOS
-running test upon the computers start up
-POST(power on self tests) which ensures that all hardware is correctly connected and functional
-checking the CPU clock, memory and processor
-testing for external memory devices
what is the role of a device driver
enable the operating system to interact with the hardware devices
describe an instance in which virtual machine may be used
-testing programs
-protection from malware
-running software compatible with different versions and types of operating systems
give one advantage and one disadvantage of intermediate code
advantage:platform indépendant,portable
disadvantage:slower execution
