Flashcards
1.2.1 System Software
Cards in this deck (46)
- 1Purpose of an operating system: Managing the ProcessorDeciding which process to execute next
Handling interruptions to the running process - 2Purpose of an operating system: Managing the MemoryLoading programs
Reusing memory when programs are closed - 3Purpose of an operating system: Handling external peripheralsDealing with I/O requests
Using device drivers to communicate with hardware - 4Purpose of an operating system: Utility ProgramsFile manager
Anti-virus
Defragmenter
Encryption
File compression - 5Purpose of an operating system: NetworkingAllowing other computers to connect and communicate to be able to share files. Via Wi-Fi or cable
- 6Purpose of an operating system: SercurityLimiting the computer what should and shouldn’t be allowed/accessed on the system. such as username and password control
- 7Purpose of an operating system: Providing an interfaceWindows, icons, menus, pointers, touch gestures to allow a person to interact with the computer
- 8Examples of an Operating SystemWindows
Linux
Unix
iOS
Android - 9The four parts of an operating system?- user iterface
- kernel
- device drivers
- system utilities - 10User interfaceThe link between a user and a computer program that allows the user to see what occurring on the screen
Command Line Interface – allows the user to interact directly with the computer system by typing in commands into a screen.
Natural Language Interface – allows the user to interact with the computer by voice alone. E.g. telephone menu - 11KernelLoading/unloading applications from memory
Scheduling tasks to run efficiently on the CPU, Memory management
File storage to and from secondary storage devices such as the hard disk
File management
Data security - 12Device drivers?
- 13System UtilitiesThe system utility carries out specific tasks.
It contains basic facilities that run in the background without user interaction e.g
Cryptographic password management
Additional utility software can be added, e.g Anti-virus utility, Disk defragmenter utility, File compression utility - 14Memory Management: PagingA method of manipulating memory which uses pages to stored code in fixed size blocks and allows programs to run despite insufficient memory.
Uses virtual memory - 15Memory Management: Paging Advantages- Computer performance is not affected by having non-contiguous Pages
- Smaller
- Fixed sizes
- Do not need to be contiguous (next to each other) - 16Memory Management: Paging Disadvantages- only load part of the program into primary memory
- Then calls up whatever extra code is required at that point in time - 17Memory Management: SegmentationA method of manipulating memory which uses segments to store code in different sized, logical sections.
Uses virtual memory - 18Memory Management: Segmentation Advantages- Can be broken up into non-contiguous memory addresses.
- 19Memory Management: Segmentation Disadvantages- Prefer to be in one piece within memory for performance reasons
- Larger
- Variable sizes - 20Memory Management: Virtual MemoryA feature of an operating system that allows a computer to replaces physical memory shortages by temporarily moving data from RAM (temporary) to disk storage (permeant).
- 21Memory Management: Virtual Memory Advantages- Data can be accessed by any device with internet access
- Data can be easily shared between devices
- Limitless amount of storage - 22Memory Management: Virtual Memory Disadvantages- Expensive if the user is wanting a lot of storage space
- Can be slow in areas with bad internet - 23The role of interrupts and interrupt service routines, within the Fetch-decode-execute cycle: Polling- CPU checks each device whether it requires attention
- this is inefficient as if a device does not need attention then it is pointless to check it - 24The role of interrupts and interrupt service routines, within the Fetch-decode-execute cycle: InterruptA device sends a signal on the control bus to the CPU to indicate that it requires attention
If there is an interrupt then the processor will stop what it is doing to service the interrupt
Interrupts have higher priority than normal instructions - 25Types of Interruptshardware, software and input/output
- 26Types of Interrupts: HardwarePower/reset button is pressed
Memory priority error (corrupt memory) - 27Types of Interrupts: SoftwareIllegal instruction encountered
Arithmetic over flow
New log-on request - 28Types of Interrupts: Input/OutputBuffer is needed empty
Signal the completion of a data transfers to/from a device - 29Interrupt Service Routine (step 1/2)1. The instruction currently being executed will be stopped for the interrupt to carry out.
2. The instruction PC will be moved into a stack where it will be held until the interrupt has been service - 30Interrupt Service Routine (step 3)If another interrupt appears during the process of the first one then the first on is put on hold and moved to the stack on top of the instruction and the second interrupt is carried out
- 31Interrupt Service Routine (step 4/5)Once this interrupt is complete the first once will be brought back to the PC (FIFO)
Once this interrupt is completed the instruction will return to the PC and carried out - 32SchedulingManages which process to execute next and how much time it allowed execute for.
- 33Round RobinEach process is fixed with a certain amount of time, Time Slice
If the process is not completed at the end of the time slice then it returns to the back of the ready queue, so the next process can have its turn
Fair, but not efficient - 34First Come First SeveredThe processes are executed in the order that they arrive.
If one process is taking a long time to execute than the other processes must wait. - 35Shortest Job FirstThe scheduler picks the processor that take the quickest amount of time and runs them until they're finished.
The scheduler needs to know how long each process will take in advance - 36Shortest Remaining TimeProcesses can be suspended if a higher priority process joins the queue
E.g Jumping a queue if you have a fast pass, multiple people can get in front of you, even if they have been on it whilst you are queuing - 37Process BlockedThe process is blocked due to it needing extra data and will be blocked until it has the data
It is in need of an input or output
Once it has the data the interrupt allows it back into the process request queue - 38Multi-level feedback queuesThe number of process ready queues is increased
Different queues have different priorities
The scheduler is able to move processes to queues as necessary - 39Distributed operating systemAllows many computers to work together to carry out a single task
- 40EmbeddedDesigned to run inside single use systems rather than general-purpose computers
- 41Multi-taskingCan run multiple programs at the same time.
- 42Multi-userAllows many users access to the system and its resources at the same time.
- 43Real-timeDesigned to carry out actions without a fixed, and assured amount of time.
- 44BIOsgets the computer system started after you turn it on and manages the data flow between the operating system and attached devices such as the hard disk, video adapter, keyboard, mouse, and printer.
- 45Device drivercontrols a particular type of device that is attached to your computer, such as a keyboard or a mouse to convert the more general input/output instructions of the operating system to messages that the device type can understand. It's kept in a file in your computer, under Windows it would be under 'registry'
- 46Virtual machinesallows one computer system (called the host) to behave like another computer system (called the guest).
Virtual machines are based on computer architectures and provide functionality of a physical computer
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- A-Level Computer Science Flashcards on 1.2.1 System Software , created by Alyssa Watson on 28/05/2018.
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