SLR4 - Operating System/Systems Software Flashcards
Explain paging
A method of manipulating memory which uses pages to store code in fixed size blocks and allows programs to run despite insufficient memory. uses virtual memory.
Explain segmentation
A method of manipulating memory which uses segments to store code in different sized, logical sections. Uses virtual memory.
Define and explain ISR
Interrupt service routine
Determines what happens when an interrupt is raised.
Define an interrupt
A signal which stops the fetch, decode, execute cycle from running normally in order to prioritise a different device.
Give some examples of interrupts
Hardware: Power pressed Memory parity error Software: Illegal instruction Arithmetic overflow New log-on request Input/output: Buffer almost empty Data transfer completion
Define a virtual machine
When software is used to take on the function of a physical machine.
Emulators provide the illusion that a program is running on native hardware.
Define and explain OS
Operating system
Software that manages the hardware, software, security and user interface of a computer.
Explain the role of the OS
Manages the interrupts in the processor.
Manages memory including paging, segmentation and virtual memory
Manages external devices: OS instructions are converted into instructions that the hardware can read by device drivers.
Manages networking: communication to other devices through protocol
Manages access requests.
Define scheduling
A way of managing the amount of time programs have in the CPU.
Define memory management
A way of ensuring that programs in memory only access their own data or any authorised shared data with other programs.
Define virtual memory
A method of freeing available memory in the RAM by moving unused program sections to the hard drive.
Define device drivers
Software which tells the OS how to communicate with a device.
Define BIOS
Basic Input Output System
Checks that the computer is functional and loads the OSs kernel into memory
The bootstrap is responsible for loading the OS into memory
Initial start up instructions are stored in ROM
BIOS settings are stored in non-volatile flash memory.
Define Intermediate code
Code between source code and machine code which can be read by virtual machines.
What are the 5 scheduling algorithms
FCFS - First Come First Served SJF - Shortest Job First RR - Round Robin SRT - Shortest Remaining Time MLFQ - Multi-level Feedback Queues
Explain FCFS
Tasks are executed to completion and in order regardless of time
Explain SJF
The shortest task is executed first to completion. The algorithm needs to know the time each job will take in advance.
Explain RR
Each task is given a certain amount of time. If it hasn’t finished it re-joins the end of the queue.
Explain SRT
The shortest task is executed to completion or until a task with a shorter remaining time joins the queue
Explain MLFQ
Multiple queues are used with different priorities and jobs are moved between the queues depending on their behaviour.
Define Distributed OS
Controls computers on a network and presents them to the user as one system.
Define Embedded OS
Specifically designed for a device and runs efficiently with little memory and low power CPUs
Define Multi-tasking OS
Allows multiple application to be open at once by switching between running programs.
Define Multi-user OS
Allows multiple users to access a computer simultaneously with individual preferences.
Define Real-time OS
Processes are always executed in a certain time frame to cater for unusually high demand, e.g. plane autopilot.
