Operating Systems

bubblesthelabrad
Mind Map by bubblesthelabrad, updated more than 1 year ago
bubblesthelabrad
Created by bubblesthelabrad about 5 years ago
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A-Level Computing (CG3) Mind Map on Operating Systems, created by bubblesthelabrad on 02/12/2015.

Resource summary

Operating Systems
1 Modes of operating systems
1.1 Single-User Single Process
1.1.1 allow the machine to be operated by only one user at a time with at most one application program loaded into main memory.
1.1.2 It can only deal with one set of input devices
1.1.3 Operating systems for handheld devices and also DOS
1.2 Multi-Programming
1.2.1 Permits multiple programs to be active at once with the operating system allowing each one a small ‘time-slice’ of processor time in turn
1.2.2 Virtual memory divides each program into pages. However, only a few pages of the program stored in memory at any one time
1.2.3 A multi-programming operating system balances the sharing of the processor among the application programs in order to achieve a good service to all.
1.3 Multi-Tasking
1.3.1 Modern operating systems are multi-tasking
1.3.2 The user can switch between one application and another
1.3.3 The computer is still only processing one thing at a time, but use of time slices makes it appear to the user that it is happening simultaneously
1.3.4 Multi-tasking is the concurrent execution of two or more tasks
1.4 Batch-Processing
1.4.1 In batch-processing mode, processing is carried out from beginning to end without user interaction.
1.4.2 Jobs prepared in this way have all their processing requirements defined in advance.
1.4.3 By using multiprogramming, a batch of several jobs can be loaded so that when executed over the same time period the processor is kept as busy as possible by switching between the jobs as and when necessary
1.4.3.1 Increases throughput
1.4.3.1.1 The total number of jobs completed per unit time, and reduces the turnaround time
1.4.3.2 Allows sharing of computer resources among many users and programs
1.4.3.3 Keeps costs down
1.4.3.4 Moves the time of job processing to when the computing resources are less busy
1.4.4 Examples are: Deleting temporary files or unused desktop icons. Archive and compression of old emails. Scheduled virus scans
1.5 Multi-Access
1.5.1 A number of users are connected to a central computer and seemingly have individual control
1.5.2 The central computer (server) determines which user is waiting for processing (polling).
1.5.2.1 Polling is checking the status of a device, as part of a repeated cycle.
1.5.2.2 Each user is allocated a time-slice of processing time
2 Scheduling
2.1 The method by which threads, processes or data flows are given access to system resources
2.1.1 Usually done to load balance and share system resources effectively or achieve a target quality of service
3 Types of the operating system
3.1 Interactive Processing
3.1.1 User supplies commands and data
3.2 Real Time
3.2.1 Handles events in parallel, responds within a set time
3.3 Disk operating system
3.3.1 Organises drives, folds and files
3.4 File Managment
3.4.1 Manages files, storage, and access rights
3.5 Network
3.5.1 When a number of computers are interconnected
3.6 Batch Processing
3.6.1 Doing several jobs without user interaction
4 Buffers
4.1 A buffer is an area of reserved memory which temporarily stores data that is in transit.
4.2 Buffers are used for input and output of data.
4.3 Data is input from a file (e.g. from a hard drive) one block at a time.
4.4 When data is to be output to a file, it is stored in a buffer, and is only transferred to the file when the buffer is full.
4.4.1 Keeps the number of transfers to a minimum and saves time
4.4.2 Needs some memory space for the buffer
4.4.3 Overcome the problem of different speeds of peripherals and processors - processors operate thousands of times faster than printers
4.4.4 Interrupts are important in bufers. As well as messages about buffer overflow interrupts can be between any peripheral device and the processor. It might be a message from a device saying there is a hardware failure
5 Operating systems Functions
5.1 Process managment
5.2 Memory Managment
5.3 I/O Control
5.4 File Managment
6 Scheduling
6.1 B = Ready and A = Running
6.1.1 B = Running and A = Blocked
6.1.1.1 B = Running and A = Ready
6.2 Tries to maximize as many jobs as possible
6.3 Maximize the user processes
6.3.1 Avoid the low priority jobs staying at the back of the queue
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