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Main Memory (Paging (Basic method (Breaks physical memory into blocks…

- - - - Pages
    - - Page offset
  - - - can be
        
        set of registers
        
        stored in memory
        
        page table base register
        
        points to table
        
        uses hardware cache
        
        Translation look-aside buffer
        
        Allow certain wired down spaces
        
        unremovable
        
        Adress space identifiers
        
        identifies each process
        
        When something is not found
        
        missed hit
  - - - kept in page table
      - Valid-invalid bit
        
        attached to each page table entry
        
        Checks is logical address is valid
      - uses
        
        page table lenth register
  - - - time-sharing environment
- - - - main memory
        
        Multiple clock ticks
        
        CPU must stall
      - Processor registers
        
        accesed in a single clock tick
        
        base register
        
        Smallest physical memory address
        
        Limit register
        
        size of the range
    - - solves length of access
  - - - Input queue
    - - to relocatable addresses
    - - The program only works on a specific memory area
    - - unkown memory relative to segments
        
        Relocatable code
    - - If the process can be moved on memory
  - - - Generated by the CPU
      - Virtual address
      - set of all logical addresses
        
        Logical address space
    - - Address seen by memory unit
        
        Loaded into memory-address register
        
        Physical address space
    - - Memory management unit
  - - - System libraries linked to
        user programs
      - Stubs are loaded
        
        tells how to load library
    - - System libraries are loaded
        into the binary image
    - - different system libraries
- - - - Code that can change in size dynamically
  - - - Degree of multiprogramming
        
        bound by partitions
      - Multiple partition method
        
        when a partition is free
        
        a process is selected
        
        to be later loaded
      - Variable partition scheme
        
        the OS keeps a table
        
        indicating which
        
        parts of memory are available
        
        hole
        
        large block of available memory
    - - how to satisfy a request of size n
        
        from a list of free holes
      - Three strategies
        
        First fit
        
        Allocate the first whole that is big enough
        
        Best fit
        
        allocate smallest whole that is big enough
        
        Worst fit
        
        Allocate larges hole
  - - - Processes are loaded and removed
        
        Free memory sis broken into little pieces
        
        There's enough memory
        
        but it's not contiguous
      - 50% rule
        
        up to one-third of memory may be unusuable
    - - Unused memory
        
        that is assigned to a program
      - solution
        
        compaction
        
        Shuffle memory contents
        
        put free memory in a block
- - - - page number
      - value of mapped page
      - pointer to the next element
  - - - two tables
        
        kernel
        
        user
- - - - collection of methods
        
        Code
        
        Global variables
        
        Heap
        
        Stacks
        
        Libraries
  - - - Segment base
      - Segment limit
      - Determines with hardware operations
- - - - to backing store
    - - backing store
        
        fast disk
      - Ready queue
        
        processes ready to run
      - Process must be idle
      - Double buffering
  - - - memory constraints
      - Apple asks applications
        to relinquish memory
      - Application state before termination