Unit 2 - November 6 Flashcards by Samara McPhail

Operating system functions

File management 
Memory management
Utility programs
User interface 
Input/output management 
Interrupt handling
Processor scheduling

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Paging

Fixed, equally sized memory blocks
Physical divisions
Made to fit sections of memory
Makes use of VM

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Segmentation

Complete sections of programs
Logical divisions
Different sized memory blocks

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Virtual memory and paging

Sections of programs not in use are temporarily moved into VM
However Disk thrashing may occur

when more time is spent reading/writing than processing

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Types of interrupt

Power fail 
Power down command 
Input/output requests 
Clock interrupt 
Schedule interrupt

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ISR

Current data moved into stack in stack frame
ISR begins
Priority considered
Executed in order of priority
When all interrupts complete lid is popped off and original values loaded back onto the registers

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Scheduling

Decides which instructions are executed when multitasking

Schedular is used to allocate efficient processor time to run each OPEN PROCESS

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Round Robin

Each job given an equal time slice
Once the job at the front of the queue has used its time slice, if it’s completed it’s removed from the queue, but if it’s unfinished it moves to the back of the queue and the next job begins processing

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First come first served

Jobs are processed in chronological order (the order they arrived in queue)
Processed to completion regardless of execution time

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Multi level feedback queue

Uses multiple queues, each ordered on priority

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Shortest job first

The queue is ordered based on the time for completion
Jobs that require the least time are moved to the front of the queue
Processor starvation

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Shortest time remaining

Queue ordered based on time LEFT for completion
Programs with least time LEFT is executed first
Processor starvation

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Distributed OS

Uses processing power of multiple computers
Presents to the user as though it is one system
Spreads the processing load

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Embedded OS

Dedicated hardware used to perform a small range of specific tasks
Has little memory and consumes less power
Program store in ROM

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Multi-User OS

A server manages permissions and access rights when users log on
Handles requests of multiple people
Allows multiple people to access at once
Scheduling program ensures fair processor time

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Multi-Tasking OS

Gives the appearance that task are being completed simultaneously
Uses time slicing to allocate CPU time

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Real-Time OS

Designed to perform tasks in a guaranteed time frame
Has plenty of redundancy to enable it to handle a sudden increase of input
Rarely runs at full capacity

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BIOS

Stored in ROM
Basic Input Output System
Stores bootstrap loader - first instructions of a computer 
Loads the OS into RAM
Checks and configures hardware POST
Power On Self Test

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Device driver

Enables communication between the OS and input/outputs by translating instructions into language the other understands

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Intermediate code

Pre compiled code that becomes platform independent

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Virtual Machine

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Software that is designed to have the same functionality as a physical computer
Code is emulated
Provides a translator for intermediate code

Emulate

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Trick code into thinking it’s running on its original hardware but it’s running on a different machine
Eg Old Arcade Games
Testing video games on different devices before release

Generic applications

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non specific purpose
Used on wide variety of tasks and can meet multiple needs
Most commonly used

Specific applications

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Specific or bespoke purpose
Little use other than deigned tasks
Usually only installed on systems where there’s direct need

Word processor

Format and manipulate text

Database software

Create and manage databases

Spreadsheet software

Create and manage spreadsheets

Other examples of application software

Multimedia - can run on multiple platforms Communication - enables communication Graphic - visually edit images and videos

Disk defragmenter

Reorganises files in hard disk so they’re sequential Reduces movement of r/w head Results in files being able to be read faster

Compression

Reduces space files take up Files can be transferred quicker Can be downloaded from internet quicker Effective cost management and saving

Automatic updates

Ensures system is kept up to date Tackles bugs and security flaws Minimises risks from malware and hackers (less vulnerable)

Encryption

Converts data into non human readable for,at using a key Symmetrical = same key to decipher Asymmetrical = different key to decipher

Anti virus

Scams against known list of viruses Uses heuristics to try identify known viruses Quarantines potential viruses and flags user User decides next steps

Automatic backup

Data in permanent storage needs to be backed up | Means you have copies of data gets lost, stolen or damaged

Open source advantages

Code can be modified Free Access to source code Can be installed on any number of computers

Open source disadvantages

Not always fully tested May be poorly supported No financial gain for creators

Closed/Proprietary advantages

Well tested Company many provide free updates Usually fully supported by creators Creators receive financial gain

Closed/Proprietary disadvantages

Cost for license Cannot modify or redistribute software Cant share with other users No access to source code

Off the shelf software

Ready made and available for anyone to purchase Cheaper than bespoke General - not designed for specific purpose

Bespoke

Specifically made for larger companies More expensive Has very specific purposes made for users requirements take longer to be created Typically only available for who/the company it was created for

COMPILER vs interpreter

Faster to execute Can run many times without needed to be recompiled Executable doesn’t require translator to run Code can’t be reversed once compiled

compiler vs INTERPRETER

Translated line by line Stops for errors If error is found no need to recompile entire program Can run on any machine with interpreter

Library

Precompiled and pretested programs which can be added into a program Saves development time

Linker

Allows already compiled object code files to be combined with the compiled program

Loader

Copies a program held on backing store into main memory ready to be executed

Examples of tokens

``` Keywords Constants Numbers Punctuation Strings Operators Identifiers ```

Lexical anlysis

Puts each code statement into form best suited for the syntax analyser Lexer reads source code Stops at white spaces or comments Code is turned into tokens

Syntax analysis

Syntax tree is built from tokens produced in previous stage | It’s the process of the language statements being checked against the rules of the language

Code generation

Produces a machine code equivalent of the source program

Code optimisation

Redundant commands are removed form the code (I.e uncalled subroutines and functions) Speeds up compilation time

Unit 2 - November 6 Flashcards

(50 cards)