1.2.1 system software Flashcards
what is an operating system
A collection of programs that work together to provide an interface between the user and a computer.
Operating systems enable the user to communicate with the computer and perform certain low-level tasks involving the
management of computer memory and resources
describe how virtual memory is used when there is not enough RAM
-A section of the hard drive is used to act as RAM
-sections of programs that are not currently in use are temporarily moved to virtual memory through paging.
-this frees up memory for other programs in RAM
similarities and differences between paging and segmentation
BOTH are used when RAMs space is inefficient, can cause disk thrashing
paging uses equal sized sections called pages
segmentation uses variable sized, logical sections called segments
give 3 functions of an operating system
-memory management
-resource management
-i/o management
-security
-user interface
-utility software
what is an interrupt
a signal generated by software or hardware to indicate to the processer that a process needs attention.
Explain the stages of the interrupt service routine
-interrupt register is checked at the end of every FDE cycle
-if there is an interrupt that is of higher priority compared to the current process the current contents of the registers in the CPU are transferred into a stack
- the relevent 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 of a higher priority the process is repeated.
-if there are no interrupts with a higher priority, the contents of the stack are popped and placed back into the special memory registers.
-the fetch decode execute cycle renews as before
are the scheduling algorithms pre-emptive or non pre-emptive
pre-emptive- RR, SRT, MLFQ
non pre-emptive-FCFS, SJF
Give one advantage and one disadvantage of using multilevel feedback queues for scheduling
Advantages- services most urgent interrupts
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 e.g life support systems, self driving cars, power systems
Describe three functions of the BIOS
-POST(power on self test) which ensures that all hardware is correctly connected and functionality.
-checking the CPU clock, memory and processor
-testing for external memory devices
what is the role of a device driver
enables the operating system to interact with hardware devices
describe an instance in which a virtual machine may be used
-testing programs
-protecting from malware
-running software compatible with different versions and types of operating systems
Give one advantage and one disadvantage of intermediate code
Advantage - platform independent, portable
Disadvantage-slower execution
Pre-emptive
Jobs are actively made to start and stop by the
operating system.
Non pre-emptive
Once a job is started, it is left alone until it is
completed.