✅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 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 is an interrupt?
A signal generated by software or hardware to indicate to the processor that a process needs attention.
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.
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
What are the advantages and disadvantages 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 a device driver?
A program that controls the operation of a specific type of device (e.g. printer, keyboard, mouse, etc.) that is part of a computer system. Manufacturers build hardware devices in different ways so a device driver provides an interface that allows the operating system and other software to interact with the device, without having to deal with the particular hardware implementation of the device.
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
What are 4 examples of operating systems?
- Windows
- MacOS
- IOS
- Android
Why is paging, segmentation and virtual memory used?
To ensure the main memory is shared efficiently between programs.
When may a software interrupt occur?
When an application program terminates or requests certain services from the operating system.
When may a hardware interrupt occur?
When an I/O operation is complete or an error such as “printer out of paper” occurs
What is a schedular?
The operating system module responsible for making sure that processor time is used as efficiently as possible.
What are the similarities and differences of paging and segmentation?
Both: Use virtual memory to swap parts of the program. And both are ways of splitting up memory.
Paging: Splits memory into equal-sized sections called pages, these can then be swapped between main memory and the hard disk as needed.
Segmentation: Splits memory into variable-sized, logical sections called segments. These are representative of the structure and logical flow of the program, with segments being allocated to blocks of code such as conditional statements or loops.
What are 5 scheduling algorithms?
- Round Robin
- First Come First Served
- Shortest Job First
- Shortest Time remaining
- Multi Level Feedback Queues
What happens in the Round Robin Scheduling algorithm?
In round robin scheduling, processor time is divided equally among all running tasks. Each time period is called a time slice. Each process gets a time slice, and if the process has not finished when this time is up, it stops running and the computer switches to the next process. The process that has been suspended will only be able to resume running when it is next allocated processor time.
What happens in the First Come First Served Scheduling algorithm?
Processes run from start to finish in the order in which the processor receives their request to run.
What is the Shortest Remaining Time Scheduling algorithm?
The processes with the shortest time to completion go first, until a different task is added with a shorter time to completion, which then takes priority.
What is the Shortest Job First Scheduling algorithm?
Processes are queued and the process that needs the shortest total time to complete goes first.
What is an advantage of the Shortest Job First scheduling algorithm?
It reduces wait times because shorter processes are removed quickly, which means that the processor can allocate more time to longer jobs.
