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Operating System - Coggle Diagram

- - - - There are many complete computer systems in this type of configuration, each with its own memory, I/O devices, CPU and OS.
    - - The scheduling of processors is decentralized. in order for each processor to apply the algorithms to determine which job to run next, a single copy of OS and a table identifying each process and its status is stored in memory that is shared by and is accessible to all processors.
    - - A single processor system where the extra slave processors are working, managed by the primary master processor. it is asymmetrical.
  - - - Unrelated processes, regardless of job, are assigned to any available processor
      - Moderate amount of synchronization required to track processes
    - - Threads are assigned to available processors
      - High degree of synchronization required, often requiring explicit instructions from the programmer
    - - Each job has its own processor
      - No explicit synchronization required
- - - - deciding to whom it should go, how much, when and where.
    - - once memory allocation is decided, specific location must be decided and information updated.
    - - each location is either allocated or unallocated (‘free’)
    - - After deallocation, status information must be updated.
  - - - An incoming job is placed in a block that is closest in size to the requests
    - - An incoming job is placed in the largest possible memory space (hole)
    - - An incoming job is placed in the first available memory space (hole) large enough to hold it
  - - - Also called burping
      - Compaction: from time to time the operating system shifts the processes so that they are contiguous and so that all the free memory is together in one block.
      - Advantages
        
        Increase memory and processor utilization
        
        Allocation of more partitions are possible
        
        Eliminates fragmentation.
      - Disadvantages
        
        Compaction time maybe substantial.
        
        Some memory space will still be unused.
        
        Memory may contain information that is never used
- - - - In the many-to-one model, many user-level threads are all mapped onto a single kernel thread.
    - - The one-to-one model creates a separate kernel thread to handle each user thread.
    - - The many-to-many model multiplexes any number of user threads onto an equal or smaller number of kernel threads, combining the best features of the one-to-one and many-to-one models.