1.2.1 - System Software

Questão	Responda
Operating systems	1.2.1- System software
Why do you need an operating system	Operating systems are used to manage the computer. They do a range of things from managing the hardware and security of a system to the programs being run and installed. They also provide an interface between the user and the computer.
Different operating systems	Windows - more familiar OS's iOS - mobile operating system used my apple for all their mobile devices Unix - unix has a few branches of OS which include linux which is an open source operating system again with various versions and also apple OSX which is used by apple on their desktops and laptops
Utility software	Disk defragment Back up Virus checking Compressing data Firewall File management
Disk defragment	New files are chopped up and are made to fit into any space there is and therefore causes for information for one program to be split up into a load of different locations across the same HDD. To fix this disk defrag takes all the fragments for each program and stores them next to each other to allow for faster reading and puts empty space at the end so newer programs are also together
Back ups	A copy of data held on the computer so that if anything goes wrong with the version in use it can be restored back to its working state. You can either completely back up a HDD or part of it depending on what you want to back up.
Anti-virus Programs	AV software identifies and removes/quarantines viruses to keep your computer safe and stop them effecting you. It is important for AV software to be up to date as new viruses are being created all the time and you never know when you could pick one up. Heuristics are used to identify the viruses as they mainly behave in similar ways.
Data compression	"Zip" files so they take up less room. Patterns in data are spotted and a marker is put in to say repeat this section.
Firewall	sdf
File management	Allows for files and folders to be moved, copied, renamed, deleted, edited, all most anything you will need to do to a file or folder.
The kernel	Every OS has a kernel. Sometimes standard across many OS's. Kernel sits in protected area of main memory so that it cant be overwritten purposely or accidentally.
Kernel uses	Memory, process, task and disk management all managed under kernel. Connects hardware to applications and applications which are running use the kernel to send a receive data to and from input and output devices.
Memory management	Primary memory - RAM Secondary memory - Secondary storage (HDD SSD flash drive etc)
Virtual memory	Using secondary storage as RAM. Happens when actual RAM runs out either Segmentation or paging takes place and causes virtual memory to be created.
Segmentation	Variable sized piece of memory is swapped from RAM to secondary storage. Commonly used for compiled programs as can be divided into logical sections.
Paging	Fixed sized piece of memory swapped from RAM to secondary strorage.
Why is memory management important?	Allows memory to be shared Manages memory allocation Reallocate memory when available Protect operating system Provide security (see above) Protects data which is running from processes which are running Allows memory to be allocated to seperate process that are in primary memory so they can run simlutaneously
Backing store/File management	Backing store is secondary storage. To get data on the secondary storage processed, it has to be loaded into RAM whether its application or file data. File management processes normally strictly controlled by access rights.
Spooling	Simultaneous Peripheral Operations On-Line. spooling is where a buffer in memory is used by devices to access the data. Spooling is used as all different components work at different speeds so by "parking" a file in a buffer all the different components can access it as and when it needs.
Advantages of spooling	Several jobs can be lined up to be managed in order. Print management software can decide the order of printing by using priorities. Useful when sharing devices over a network. Reduces delay mismatch between devices.
Interrupt Handling	Event that alters the sequence of instructions which the processor is executing from a planned sequence. Lots of things that cause an interrupt but they all need to be able to go back to where it was in the sequence when it is free.
Reasons for interrupts.	Obtaining processor time Higher priority tasks need to be run first Ensure all data safely stored Ensure highest priority jobs are completed first Indicate processor load Indicate servicing requirements for a device
Sources of interrupts	Hardware (Printer) buffer is empty/reset button being pressed. This can be resumed after interrupt has finished. Clock interrupt. Software - OS requestions CPU time. Power failure. System failure. User interrupt - new user trying to login.
priority and interrupt management	Interrupts are allocated a priority which is used to work out where the interrupt will be processed. Interrupt with highest priority will be done first. Highest priority isn't always most important task - some small tasks may be performed first to get them out the way. Generally interrupts are followed by normal service (fetch-decode-execute), however when the system is interrupted by a login request or a printer status request it manages this by copying values from registers, then storing them in a stack and putting them back in registers after task complete.
Scheduling, Job queues and priorities	Uses processor time and resources more effectively Gives more users opportunity to use the system Gives users a more optimized feeling system Gets the highest amount of data flowing through the system Processes urgent tasks first
Methods of scheduling	Round Robin (RR) - Each task is allocated a VERY SMALL time slice. When the time slice has been served the next time slice starts for another task and so on. Because the time slices are so small on one notices their tasks not getting fully processed. Priority - The tasks are processed in descending order e.g. most important first Shortest Job First (SJF) - Process tasks in ascending time to complete e.g. shortest task first First Come First Serve (FCFS) - Do tasks in order. Normally used in printer queues.
Different types of OS and their uses	Operating systems have to suit different kinds of work that it will be required to complete. The following systems are designed to do slightly different things.
Multi-User OS	This will enable many users to be logged into a single system at any time. So this is a single computer which has many terminals so many users can work at the same time. For example online gaming or supermarket checkout systems.
How it works	Each terminal gets a time slice and these slices are rotated in turn. each time slice is around 1/100th of a second so the users are unaware of this switching. Indicators are used to show who has the processing power at that point. Priorities and user access rights are associated with each persons login. Each users data is kept separate and security is carefully manged.
Multi-Tasking OS	These are used when any user needs to run multiple tasks at the same time. However in reality the tasks are running simultaneously but it appears they are as they are all "open" at the same time. Windows is a multi-tasking OS and it would be common for you to be writing a report whilst listening to music and with facebook open in the background.
How it works	Processor is fast so user has the impression that not all tasks are running concurrently. Each task is cycled through in turn with each task having a short amount of time between being turned on and off. The user can switch between programs with each program being in a separate window.
Multi-User, Multi-Tasking OS	The two above OS's can actually be combined together to create a networked system used in business or school where everyone accesses the applications software at the same time.
Embedded system	Most every day items have this type of system. They are simplified computer systems which have limited functions

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