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OPERATING SYSTEM - Coggle Diagram

- - - - File management system can be define as a system that an operating system uses to keep track of different files
      - There are several functions that must be performed by an efficient file system
        
        appending the stored files and protecting the files from loss of data
        
        Organize and keep track of files
        
        accessing the stored files
        
        Provide an appropriate naming system for files
        
        include storing of files in an orderly fashion
        
        Provide a standardized set I/O interface routines
        
        Ensure the data in the file is valid
      - File Access Techniques
        
        Direct
        
        Direct
        
        Sequential
      - 4 Types of Directory Structure
        
        Directory structure
        
        Single-level directory
        
        Storage structure
        
        Two-level directory
      - Methods of File Allocation
        
        Almost every case, many files are stored on the same disk.
        The main problem is how to allocate space to these files so that disk space is utilized effectively and files can be accessed quickly
        
        Three major methods of allocating disk space are in wide use
        
        Contiguous file allocation
        
        Linked file allocation
        
        Indexed file allocation
      - Contiguous File Allocation
        
        Advantages
        
        Any record found once starting address, size known
        
        Easy direct access
        
        Disadvantage
        
        Difficult file expansion, fragmentation
      - Linked List Non-Contiguous
        
        Storage level
        
        Directory entry
        
        Filename, storage location of first extent, location of last extent, total number of extents (not counting first)
        
        Each extent points to next one in sequence
        
        Directory level
        
        Each extent listed with physical address, size, pointer to next extent
        
        Null pointer indicates last one
        
        Disadvantage
        
        No direct access support
        Cannot determine specific record’s exact location
        
        Advantages
        
        Eliminates external storage fragmentation
        
        Eliminates need for compaction
      - Free Space Management
        
        Since disk space is limited
        Need to reuse the space from deleted files for new files
        
        Free space management is implemented by this technique
        
        Using bitmaps
        
        Linked List
- - - - Booting the computer,
      - Handles system resources
      - Performs basic computer tasks
      - Provides file management
      - Provides a user interface
      - Provide Security management
      - Make sure all the user tasks can be done properly
      - Translate user command
      - Conduct the errors if occurred
      - Conduct input/output
    - - Layered
      - Microkernel
      - Monolithic
      - Networked and distributed
    - - OS is similar to government . Like a government, it performs no useful function by itself.
      - An OS is a program that manages the computer hardware
    - - Multiprocessor system
      - Clustered system
      - Single processor system
    - - Open Source Operating System
      - Closed Source Operating System
    - - Time Sharing
      - Buffering
      - Multiprogramming
      - Spooling
      - Multitasking
      - Caching
    - - Kernel
      - File System
      - Kernel
    - - Voice Actuated
      - Voice Actuated
      - Command Line
      - Web Form
- - - - Memory manager in charge of main memory.
      - Check the validity of each request for memory space
      - Primary function of memory manager is to preserve the space in main memory occupied by the operating system itself
    - - Main – the system RAM and controller cards.
      - On-line mass storage – Secondary storage.
      - Internal – Processor registers and cache.
      - Off-line bulk storage – Tertiary and Off-line storage.
    - - Placement
        
        Best fit
        
        Worst fit
        
        First fit
      - Replacement
      - Fetch
    - - Key control information comes first followed by the various resident operating system routines.
      - The remaining memory, called the transient area, is where application programs and transient operating system routines are loaded.
      - Generally, the operating system occupies low memory beginning with address 0.
    - - Swap – out operation: by copying its instruction and data onto a disk. This operation frees the area of memory that was allocated to the process.
      - Swap – in operation : by loads another process in this area of memory.
    - - Divides the available space into fixed-length partitions, each of which holds one program.
      - This would allow several user jobs to reside in the memory
    - - Method
      - Object
      - Function
      - Local variable, global variable,
      - Procedure
      - Stack, array ,symbol table
      - Main program ,subroutine
    - - Addresses are dynamically translated as the program runs. When an instruction is fetched, its base-plus displacement addresses are expanded to absolute addresses by hardware.
      - Addresses consist of two parts , a page number in the high-order positions and a displacement in the low-order bits.
      - Like segments, a program’s pages are loaded into noncontiguous memory.
      - A program’s segments can vary in length
    - - Shortest Job First
      - Priority
      - Round Robin
      - Multilevel Queue
      - First In First Out (FIFO)
      - Multilevel Feedback Queue
    - - Thread is basic unit of execution
      - A thread is also known as light weight process.
      - Thread is a single sequential flow of control within a program.
      - A process can have many threads of execution
    - - This means memory utilization would be bettered using multithreading
      - Concurrent execution of threads would result in faster execution of the process.
      - Multiple thread in a process share the same memory address space.
    - - Refer to a specific condition when two or more process are waiting for each other release a resource.
      - A deadlock will occurs in a computer system if all the following conditions hold simultaneously.
    - - Hold and Wait – condition means a situation where in a process owns a resource and claiming the other resource
      - No preemption– condition means a situation where the granted resource to a process cannot be taken back by the operating system forcibly.
      - Mutual Exclusion – means that a resource is assigned to only one process at a time.
      - Circular wait– is a situation where each waiting process is waiting for the next process in the chain and none is able to get the resource.
    - - Detect and Recover from Deadlock
      - Ignore the deadlock
      - Prevention and avoidance of deadlock
      - Avoid the deadlock