1.2.1 Systems Software Flashcards
What is an operating system?
A collection of programs that work together to provide an interface between the user and the computer
Give 3 functions of an operating system.
Three from:
- 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: Uses equal-sized sections 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 to act 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 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 place back into the
special memory registers
● The fetch-Decode-Execute cycle renews as before
Are these scheduling algorithms
pre-emptive or non pre-emptive?
FCFS, SRT, SJF, MLFQ, RR
Pre-emptive: RR, SRT, MLFQ
Non-preemptive: FCFS, SJF
Give one advantage and disadvantage of using
Multilevel Feedback Queues for scheduling.
Advantage: Services most urgent
interrupts first
Disadvantage: 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 support systems,
self-driving cars, power systems.
Describe three functions of the BIOS
Running tests upon the computer’s start-up:
● POST (Power-on self test) 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 hardware devices.
Describe an instance in which a 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 independent,
portable
Disadvantage: Slower execution
