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TYPES OF SOFTWARE (System software (Types : (Operating system (Need :…

- - - - Program which acts as an interface between user and the hardware
      - Called as resource manager
      - Need :
        
        User interface
        Way to interact with the user either through GUI of commmand prompt
        
        Program execution
        OS loads necessary into the comp memory which are required for proper functioning
        
        Resource allocation
        OS controls and allocates the system resourses like CPU time and memory
        
        Manipulation of files
        OS manages the format in which info is stored and retrieved from the hard disk
        
        I/O operations
        Handles all input ouput operations
        
        Errror detection
        OS performs the main function of error detection and handling
      - Functions :
        
        Processor management
        
        CPU management
        CPU scheduling
        
        Which resident prg will be executed next
        
        Managing the sequence of process of programs to be executed
        
        2 types of scheduling
        
        Non-preemtive scheduling
        
        Scheduled job is always completed before the next job is made
        
        3 techniques:
        
        First come -first served FCFS
        
        2 more items...
        
        Shortest job next scheduling
        
        1 more item...
        
        Deadline scheduling
        Priority Scheduling
        
        1 more item...
        
        Preemtive scheduling
        
        A scheduling decision can be made even while the job is in execution
        
        Round robin :
        
        Each prg is given a fixed amt of time to execute
        
        CPU continues with the execution till the allted time is over or there is some interupt request
        
        If the task is not completed and the alloted time expires it is put at the end of the queue
        
        Each task gets alloted share of CPU time
        
        Very useful in network environment
        
        Memory management
        
        Process of allocation and deallocation of memory -memory management
        
        Common MM techniques:
        
        Partitioning
        
        The total memory is divided into various partitions of same size or diff sizes
        This helps to accommodate a no. of programs into the memory
        
        2 types :
        
        Fixed
        
        1 more item...
        
        Variable
        
        3 more items...
        
        Virtual memory
        
        Demand paging
        
        Used by OS so that user can load programs which are larger than the main memory
        
        Program is executed even if the complete program is not loaded into the main memory
        
        Process :
        
        OS divides the main memory into equal sizes called pages
        
        A part of the program resides in the main memory - active set
        The rest will be in the secondary memory
        
        When a required page is not in the main memory on demand, tge OS now swaps the required page with an already executed one
        
        Device management
        
        Job of the OS is to communicate between devices and hardware
        
        2 techniques:
        
        Buffering
        
        Maybe be used when moving between 2 processors within a computer
        
        Data is stored in the buffer as it is recieved from one process or just before its sent to another process
        
        Overlaps input output of one job woth the computation of the same job
        
        Increases the efficiency of the computer
        
        Less efficient than spooling
        
        Buffering takes the part of the main memory as buffer
        
        Overlapping technique
        
        Spooling
        
        Hard disk used a buffer
        
        Overlaps input output of one job with computation of another job
        
        More efficient increases efficiency of a computer
        
        Simultaneous peripheral operations on line
        
        Processing of diff task on the same I/O device
        
        File management
        
        Data or info are usually stored in secondary storage device -hard dosk
        
        OS maintains tge files using file allocation table -FAT
        
        FAT stores info about the file like file name , type of file,size , address etc
        
        When a new file is created or copied on a disk , the OS calls the file manager to perform the tadktask i
        
        Fike manager searches the disk for a soace , allocates to a fike abd makes appropriate entries to tge FAT
      - Types :
        
        Single user OS
        
        Used as a stand alone for performing a single task
        Eg. Pc
        
        Multiuser OS
        
        Many comps that allows data and and application to be accessed by multiple users at the same time
        
        Multiprocessing OS
        
        Has 2 or more processors for a single running process
        
        Processing takes place paralleled
        
        Each processor works on different processor at the same time
        
        Real time OS
        
        Eg . Computer that controls machines, online reservation systems
        
        These system are required to work refined time constraints
        
        Time sharing OS
        
        Supports round robin
        
        Many users simultaneously share CPU time
        
        The system swtched from one user to another giving the impression to the user that each has a separate comp system
      - Commonly used OS
        
        Windows
        
        Linux - only free ans open spurce software
        
        BOSS- bharat OS solutions
        Indian distribution of Linux
        
        Unix - one of the firsts
        Multiuser OS
        
        Solaris - Unix baes OS
        Sun Microsystems
        
        Mobile OS
        
        Android - Linux derived
        Google's free and open source software
        
        iOS - apple
        
        Windows 10 - mobile
      - OS as resource manager:
        
        Monitors diff resources
        
        Decides which prg gets which resource , when and for how much time
        
        Allocates the resources
        
        Reclaims the resources
    - - Code in high level language - source prg
        Machine code - object prg
      - It is a language which converts source code to machine code
      - Source code - translator - object code - linker - executable code
      - Types :
        
        Assemblers
        
        Convert prgs written in machine language
        
        Compilers
        
        Converts complete source program as a whole into machine code
        
        It converts it into machine code successfully only if it is free of errors
        
        All the errors are traced and displayed with line number
        
        The prg will occupy less memory space
        The prg doesnt reside in memory once it compiled
        
        Intepreters
        
        Debugs the prg line by line
        
        Displays line by line
        Doesnt move to the next till the error in the current lone is removed
        
        Prg will occupy more memory space than a compiled one
        
        Translates single statement of the source code into machine code and executes it immediately before going on to the next
- - - - Detects and removes viruses
      - Types of viruses :
        
        Boot sector virus
        
        The virus gets copied into the boot sector
        (Where prgs to boot the machine is stored)
        
        Virus loaded to the main memory and then to OS
        
        Antivirus overwrites the infected boot sector
        
        File virus
        
        Affects executable files
        
        Memory residents and wait in the memory until the user runs another prg
        
        While another prg is running the virus replicates
        
        Macro virus
        
        Affects .doc of MS Word
        
        Changes the formatting of the document
        
        May not allow editing or saving
        
        Trojan horse
        
        Generally hidded in games or spreadsheets
        
        Prg will look like it is functioning normally when it is being destroyed
        
        Doesnt require a host prg to attach itself
        
        Complete prg - main objective is to harm data
        
        It destroys FAT
        
        Worms
        
        Prg capable of replicating itself on a comp network
        
        Travel across 1 comp to other across communication links/lines
        
        Doesnt require a host prg
    - - Helpsto rearrange files and unused spaces on the hard disk
      - Scans the harddisk and brings all the fragments together
    - - Helps in taking backup of the data
    - - Helps in compression of large files so that it takes less space
      - These can be exploded when required
    - - Scans files that not been used since long
      - Prompts the user to delete such files so as to create more space
    - - Prgs that control a particular type of device that is connected to a printer
- - - - Software made for day to day application
      - Types :
        
        Word processor
        
        Used to create documents
        
        MS Word
        
        Prsentation tools
        
        Creating presentations and also for diff types of audio, video etc
        
        PowerPoint
        
        Spreadsheet package
        
        Store and create data in a tabular column
        
        Can create graphs and charts from data
        
        Lotus 123
        MS Excel
        
        Database management system
        
        Create and maintain database for an organisation
        
        Impoerting and exporting of data from other prgs allowed
        
        MS Access
    - - Tailored as per user's requirements
      - Types:
        
        Inventory management system
        
        Department stores to keep record of stock
        
        School management system
        
        Manages school data
        
        Payroll system
        
        Used by an organisation to keep track of employee salaries
        
        Hotel management
        
        Reservation system
        
        Weatger forecasting system
- - - - Pay the supplier for a copy of the software and get permission to use it
    - - For trial purpose that the user is allowed to try for free for a specified period of time
    - - Free of cost and is usually bundled up with some operating system
      - Internet explorer- Microsoft OS
      - Source code not availible so modification cannot be done
    - - Gives the freedom to use , modify and redistribute the software free of charge
      - Python