Flashcards
SLR 1.4 Operating Systems
Cards in this deck (21)
- 1Operating system roleProvides the interface between the user and the hardware.
The role of the Operating System is to provide a platform on which a specific application software can run. - 2Utility programs role and examplesoftware programs that add functionality to your computer or help your computer perform better.
Encryption software
compression software
Defragmentation software
Antivirus software - 3File managementData is stored in files.
An extension to the filename tells the operating system which application to load the file into.
The operating system may present a logical structure of files in folders and allow the user to rename, delete , copy and move files. - 4User managementAllows multiple users to log into the same computer. The operating system will retain settings for each user such as icons, desktop backgrounds etc.
Each user may have different access rights to files and programs. - 5User interfaceWIMP: Windows, Icons, menus and pointers
visual
interactive
intuitive
Optimised for mouse and touch gesture input - 6Paging-Programs are split up to fit into a given number of pages
-Paging takes no account of how it splits the program, only that it splits it into fixed-size pages. It could separate the instructions inside a looping condition so they are in different pages which would not be very efficient. - 7SegmentationBased on logical divisions, segmentation splits up the program into two parts and places them in the available free space, leaving two smaller areas of free space
- 8Paging vs Segmentation similarities and differencesBoth allow programs to run despite insufficient memory
-Pages and segments are stored on disk
-Pages and segments are transferred into memory when needed
-Pages are fixed size whereas segments are different sizes
-Pages are made to fit sections of memory. Segments are complete sections of programs
-Pages are physical divisions whereas segments are logical - 9Virtual memoryInstructions that are not being used are transferred to virtual memory on the hard disk.When these instructions are needed again, a different program can be swapped out of RAM to virtual memory to make room for the instructions that are now needed.
- 10InterruptsInterrupts present a problem - the processor will need to stop executing its current program to run code for the interrupt, known as the interrupt service routine .
Interrupts have higher priority than normal programs - 11Interrupt service routineset of instructions that need to be fetched, decoded and executed to carry out the operations of the interrupt.
contents of the program counter need to be changed to point to the address for the first instruction of the interrupt.
When an interrupt is received, the values held in the registers are copied into a data structure in memory known as the stack - 12Stack Framevalues are pushed onto the stack in a stack frame, effectively saving them for later retrieval.
this allows us to:
Retrieve the previous values for the original program
Load them back into the processor registers
Carry on executing the original program where we left off.
- 13Types of interrupts and examplesHardware
-Power supply failure
-Power reset button pressed
-Power down command
User
-Moving the mouse
-Clicking an icon
-Keyboard presses
Software
-Illegal instruction encountered
-Arithmetic overflow
-New log on request
Timer
-Data-logging program reading an input sensor every second
-Screen recording application
InputOutput Devices
-Buffer nearly empty
-Signal the completion of data transfer to/from a device.
-Printer ink supply information - 14SchedulerIn a multiuser environment, a number of users will need servicing seemingly at the same time. For this to be possible, operating systems need a scheduler.
A scheduler manages:
Which process to execute next
The length of time the next process can execute for - 15Scheduling algorithmsFCFS (first come first serve Non-preemptive)
-Processes are executed in the order they arrive
If a process take a long time, others behind it simply have to wait
SJF (Shortest Job First Non-Preemptive)
-Picks the processes that take the shortest amount of time and runs them until they finish.
(Scheduler needs to know how long each process will take)
RR (Round Robin Preemptive)
-Each process is allocated a fixed amount of time. If the process is not complete by the end of its time slice, it returns to the back of the ready queue
SRT (Shortest Remaining Tme Preemptive)
-Similar to SJF however, SRT is preemptive meaning processes can be suspended if a higher-priority process joins the queue
MLFQ (Multi-level feedback queue Preemptive)
-If a computer system has more than one processor or processor core, it can handle more than one process queue at a time.
WIth a MLFQ, different queues can have different priorities, and the scheduler can move jobs between the different queues as needed. - 16Types of Operating SystemMulti-user opeating system
-The computer will manage the user’s various permissions and access rights when they log on.
-Server operating system software will handle the requests of multiple people using different computers on a network at the same time.
Distributed operating systems
-operating systems controls and coordinates the computers, presenting them to the user as if they were a single system
Embedded operating system
-Run on dedicated hardware so they run with maximum efficiency, using low-powered processors and very little memory.
Real time operating system
-guaranteed to execute within a known time frame
Plenty of redundancy is built into these systems so they can handle sudden increases in input - 17BIOSThe Basic Input Output System (BIOS) is responsible for loading the operating system when the computer first turns on.
It first checks that all the hardware it needs is connected and working using a Power-On-Self-Test (POST)
A boot loader program (bootstrap) is used to load the operating system kernel into memory.
Initial start-up instructions are stored on ROM.
BIOS settings are stored in flash memory so they can be changed and are retained when the power is switched off. - 18Device driverSoftware that tells the operating system how to communicate with a device
The device driver translates the operating system’s instruction to print the document into a series of instructions that a specific set of hardware will understand. - 19Virtual MachineA program that has the same functionality as a physical computer.
Emulators trick a program into thinking it’s running on its native hardware when, in fact, it’s running on an entirely different machine. - 20Advantages of using Virtual MachinesAs demand on the network increases, additional servers can be spun up and the load balanced across different physical devices.
Another major advantage of this is if one server stops working, the others can pick up the load and continue working as if nothing happened. - 21Java BytecodeJava code is designed to run on many different platforms
Java gets around this by compiling its code into a half-way code known as bytecode.
This code is translated by a java Virtual Machine (JVM) running on a target device, which then translates it into specific machine code.
This process makes the code highly portable between devices
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- Cambridge Computing SLR 1 Flashcards on SLR 1.4 Operating Systems, created by Alan Szelast on 16/10/2021.
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