1.2.1 - Systems software Flashcards
What is the Operating System?
Collection of programs that provide an interface between the user and computer. It enables the user to communicate with the computer and perform tasks involving the management of computer memory and resources e.g Windows
What does an Operating System provide?
- Memory Management
- Resource Management
- File Management
- Input / output Management
- Interrupt Management
- Utility Software
- Security
- User Interface
What is Paging?
When memory is split up into equal - sized sections known as pages. These can be swapped between main memory and the hard disk as needed
What is Segmentation?
Splitting of memory into logical sized divisions known as segments, which vary in size. These represent the structure and logical flow of the program
What does Virtual Memory do?
Uses a section of the hard drive to act as RAM when the space in main memory is insufficient to store programs being used. Sections of programs not currently being used are temporarily moved into virtual memory through paging, freeing up memory for other pages in RAM
What is Disk Thrashing?
When the computer “freezes” due to pages being swapped too frequently between the hard disk and main memory. The issue becomes progressively worse as virtual memory is filled up
What is an Interrupt?
Signals generated by software or hardware to indicate to the processor that a process needs attention. They have different priorities and how urgent they are must be taken into account by the OS when allocating processor time. They are stored within a priority queue in an interrupt register
What is the Interrupt Service Routine?
When the processor checks the contents of the interrupt register at the end of the FDE cycle. If an interrupt exists that is of higher priority to the process being executed, the current contents of the special purpose registers in the CPU are temporarily transferred into a stack. The processor then responds to the interrupt by loading the appropriate ISR into RAM. A flag is set to signal the ISR has begun. Once the interrupt has been serviced, the flag is reset. The interrupt queue is checked again.
What is Scheduling?
To make sure each section of the program being run receives a fair amount of processing time
What is a Pre - Emptive Scheduling Algorithm?
Jobs are actively made to stop and start by the OS
What is a Non Pre - Emptive Scheduling Algorithm?
Once a job is started, it is left alone until compiled
What is Round Robin?
Each job is given a section of processor time - a time slice - within which it is allowed to execute. Once each job in the queue has used its first time slice, the process is repeated until a job has been completed at which it is removed from the queue
What is an Advantage of Round Robin?
All jobs are attended to
What are Disadvantages of Round Robin?
- Longer jobs will take much longer
- No job priority or urgency
