Section 2 - Systems Software Flashcards
Functions of an operating system, Types of operating system, The nature of applications, Programming language translators (83 cards)
Operating System
Set of programs that manages the operations of the computer for the user. It acts as a bridge between the user and the computer’s hardware
Operating Systems location
Held in permanent storage, for example on a hard disk
Loader
Held in ROM. When a computer is switched on, the loader in ROM sends instructions to load the operating system by copying it from storage into RAM.
Operating System Functions
- User Interface
- Memory Management
- Interrupt Service Routines
- Processor Scheduling
- Backing Store Management
- Mangement of all Input and Output
Memory Management
Each program must be allocated a specific area of memory whilst the computer is running. Should a user wish to switch from one application to another in a separate window, each application must be stored in memory simultaneously.
Types of Memory Management
Paging
Segmentation
Paging
Memory is divided into fixed size pages of 4kb each, and a process currently in memory may be held in several non-continuous pages.
Paging Table
Uses mapping to store a link between physical memory address and the logical address space of each process.
Segmentation
Logical divine of address space into varying length segments which depend on the program structure.
What can paging and segmentation both do?
Possible to load only a part of a program into memory initially.
What is virtual memory?
Operating system may swap pages of temporarily inactive jobs out to disk, using secondary storage as an extension of memory to make room for the next job which has a share of processor time.
What is an interrupt?
An interrupt is a signal from a software program, hardware device or internal clock to the CPU.
When does a software interrupt occur?
When an application terminates or requests certain services from the operating system.
When does a hardware interrupt occur?
When an I/O operation is complete or an error such as “Printer out of paper” occurs.
Give some examples of interrupts in descending order of priority.
- Power-fail interrupt
- Clock interrupt
- An I/O device sends a signal requesting service or signalling end of I.O operation.
What is the Scheduler?
The operating system module responsible for making sure that processor time is used as efficiently as possible.
Main objectives of the Scheduler?
- Maximise throughput
- Be fair to all users on a multi-user system
- Provide acceptable response time to all users
- Ensure hardware resources are kept as busy as possible.
Types of Scheduling Algorithm
Round Robin First come first served Shortest remaining time Shortest job first Multi-level feedback queues
What is round robin
Processes are despatched on a first in first out (FIFO) basis, with each process in turn being given a limited amount of CPU time called a time slice or quantum.
What is first come first served?
Jobs are processed in the order in which they arrive, with no system of priorities.
What is shortest remaining time?
The process with the smallest estimated time to completion is run next.
What is shortest job first?
The process with he smallest estimated running time is run next.
What is Multi-Level feedback queues designed to do?
- Give preference to short jobs
- Give preference to I/O bound processes
- Separate processes into categories based on their need for the processor.
How does multi-level feedback queues work?
The algorithm implements several jobs queues and jobs can move between queues, depending on how much processor time they use. Since I/O is so much slower than processor speed, it is efficient to try keep the I/O devices as continuously busy as possible, so that a bottleneck does not occur when several programs simultaneously need to send back to the printer.