SYSTEMS SOFTWARE Flashcards
What is an operating system
Software that controls the computer, manages the computer’s hardware and the programs running on it
Examples of OS
Windows, MacOS, Linux, IOS and Android
Roles of an operating systems
- Manage the system hardware
- Manage the installation and running of programs
- Manage the security of the system
- Provide a user interface
- Memory management
What is paging
Programs are physically divided into equal-sized blocks called pages
What is segmentation
Programs are logically divided into unequal blocks containing modules or routines
What is virtual memory
The use of secondary storage as an extension of a computer’s physical memory
What is disk thrashing
When pages are being swapped from main memory to virtual memory too often, slowing down the computer
What is an interrupt
A signal sent to a CPU to signify another processor is in need of processing time
What is the ISR
Interrupt Service Routine - This is the program code that is called when an interrupt is triggered
What happens when an interrupt occurs
- The contents of the PC and other registers are copied to an area of memory called a stack
- The ISR can be loaded by changing the PC to the location of the ISR in memory
- When the ISR is completed the previous content is restored from the stack to the CPU
What happens when an interrupt is being serviced, a higher priority interrupt occurs
The interrupt will be added to the stack and the new interrupt is serviced. After, the previous interrupt is taken off the stack and continued
What is scheduling
The method an OS uses to ensure all processes get sufficient processor time
Describe the round robin algorithm
Each process is given a fixed amount of time. If it hasn’t finished by the end of that time period, it goes to the back of the queue so the next process in line can have its turn
Describe the first come first served algorithm
The first process to arrive is dealt with by the CPU until it’s finished. Any other processes that come along are queued up waiting for their turn
Describe the shortest job first algorithm
Picks the job that will take the shortest time and run it until it finishes
Describe the shortest remaining time algorithm
The scheduler estimates how long each process will take. It then runs the one that will take the least amount of time. If a process hasn’t completed after a certain amount of time, the scheduler checks to see whether any shorter process have been added
Describe the multilevel feedback queues algorithm
Uses multiple queues. Each of these queues has a different priority. The algorithm can move jobs between these queues depending on the jobs behaviour
Describe distributed OS and an example where it is used
Allows multiple computers to work together on a single task. They tend to be used in systems aimed at completing computationally intensive tasks.
e.g 3D animation
What are embedded systems and an example of one
A dedicated computer system that performs one or more specific functions within a larger piece of equipment.
e.g, washing machines, vending machines
Describe multitasking OS
Can run multiple programs simultaneously
Describe multi-user OS and an example where it is used
Allows multiple users to use a system and its resources simultaneously.
e.g Banks and retailers
Describe real-time OS and an example where it is used
Designed to carry out actions within a guaranteed amount of time even when left running on long periods. Usually the expected response time is within a small fraction of a second
e.g autopilot
What is the BIOS
Basic Input/Output System - The program a computer’s microprocessor uses to start the computer system after it is powered on
What is a device driver
A piece of software that tells the computer how it can communicate with hardware
What is a virtual machine
A program that has the same functionality as a physical machine
Uses of virtual machines
- Run one OS within another OS
- a program needed that can’t run on the host OS
- offers a convenient way to test a program being developed on multiple platforms - Interpreting intermediate code
