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