1.2.1 Operating System Flashcards
What does BIOS stand for?
Basic input output system
What is the BIOS?
A program that initialises and tests whether system hardware is functional and then loads the operating system from the hard disk into RAM
What are device drivers?
A program supplied with a peripheral device that allows the OS to control and communicate with the device
What are distributed operating systems?
This is a type of operating system that is run across multiple devices, allowing the load to be spread across multiple computer processors when a task is run.
What is an embedded operating system?
Built to perform a small range of specific tasks, this operating system is catered towards a specific device.
They are limited in their functionality and hard to update although they consume significantly less power than other types of OS.
What is intermediate code?
Code partly translated between high-level and machine language produced by a computer
What are interupts?
A signal from hardware, software or the clock to alert the CPU.
If the interrupt is a higher priority than the current task the current routine pauses and resumes after the interrupt is executed.
What are interrupt service routines (ISR)?
If an interrupt is a higher priority than the current task, register contents are temporarily transferred onto the system stack at the end of the current FDE cycle and the interrupt is handled.
What is memory management?
The efficient organisation and allocation of main memory to the programs in use
What are multi-level feedback queues?
A scheduling algorithm that uses multiple queues, each with a different priority. Jobs can be moved between queues
What are multi-tasking operating systems?
Multi-tasking operating systems enable the user to carry out tasks seemingly simultaneously.
This is done by using time slicing to switch quickly between programs and applications in memory.
What are multi-user operating systems?
An operating system consisting of one mainframe computer with multiple terminals that allow multiple users to access the computers resources.
Each user is given a time slice of the mainframe processor.
What is the operating system?
A set of programs managing the operation of the computer that is loaded into RAM every time the computer is turned on.
It bridges the user to the hardware.
What are real-time operating systems?
An operating system where data is processed as it comes, with response generated with a guaranteed timeframe.
Commonly used in time-critical computer systems.
What is a virtual machine?
Any instance where software is used to take on the function of a machine, including intermediate code or running an operating system within another.
What is paging?
Paging is when memory is split into equal-sized sections known as pages, with programs comprising a certain number of equally-sized pages.
These can then be swapped between the main memory and the hard disk.
What is scheduling?
Allocating processor time to each application to ensure processor time us used as efficiently as possible when multitasking
What is segmentation?
Segmentation is the splitting up of memory into logical-sized divisions, known as segments, which vary in size.
These represent the program’s structure and logical flow, with segments allocated to blocks of code such as conditional statements or loops.
What is virtual memory?
Virtual memory 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 that are not currently in use are temporarily moved into virtual memory through paging, freeing up memory for other programs in RAM.
What eight things does the operating system do?
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Security
Utility software
File management
Input/output management
Resource management
Interrupt management
Memory management
User interface
Describe Round robin scheduling
Each job is given a section of processor time - known as a time slice - within which it is allowed to execute.
Once each job in the queue has used its first time slice, the operating system again grants each job an equal slice of processor time.
Once a job has been completed it is removed from the queue.
What are two negatives about round robin scheduling?
Although Round Robin ensures each job is seen, longer jobs will take a much longer time for completion due to their execution being inefficiently split up into multiple cycles.
This algorithm also does not take into account job priority.
Describe First come first served scheduling
Jobs are processed in chronological order by which they entered the queue. Although this is straightforward to implement.
What is a negative about first come first served?
FCFS again does not allocate processor time based on priority.
What is a negative about multilevel feedback queues?
Can be difficult to implement due to deciding which job to prioritise based on a combination of priorities.
Describe shortest job first scheduling
The queue storing jobs to be processed is ordered according to the time required for completion, with the longest jobs being serviced at the end.
This type of scheduling is most suited to batch systems, where shorter jobs are given preference to minimise waiting time.
What are two negatives of shortest job first scheduling?
It requires the processor to know or calculate how long each job will take and this is not always possible. There is also a risk of processor starvation if short jobs continue being added to the job queue.
What is processor starvation?
When a particular process does not recieve enough processor time in order to execute and be completed.
What is the POST?
POST (Power-on self test) which ensures that all hardware (keyboards, disk drives) are correctly connected and functional
What are 2 uses of virtual machines?
Protection from malware: Malware will affect the virtual machine rather than the device being used.
Running incompatible software: Programs specific to different operating systems or different versions of an operating system can be run within a VM, saving the time and money required to purchase the hardware.
