A high-level program language code must be compiled , link , Load to enter memory ,

Create process at program runtime

 

link : Link the compiled target module into an executable program . There are static links and dynamic links .

 

Static link : Before the program runs , Link the target module into a complete load module

Two tasks to be done :1. Modify logical address

                                2. Transform external call symbols

Advantages and disadvantages

            advantage : The program runs faster

            shortcoming : When the program file is large , It takes up a lot of internal and external storage space , High storage overhead . Program development is not flexible enough , convenient . Modifying the first mock exam will lead to a relink to the entire program .

 

dynamic link : Postpone links to some target modules until the program runs ( When functions in these modules are called to execute ) Only then .

Advantages and disadvantages

            advantage : Save internal and external storage space , It is convenient for program development

            shortcoming : The program runs slower

 

 

load : Memory needs to be allocated for the process and the required data , Load into memory .

absolute loading : The object code that generates the physical address at compile time , When loading, the program and data are loaded into memory according to the physical address of the loading module

Relocatable loading ( Static relocation ): Relocatable code that generates logical addresses at compile time , When loading, modify the instruction and data address in the object code

In dynamic operation ( Dynamic relocation ): Address mapping is deferred until the process is executed

 

Memory space allocation : Allocate memory space for processes , There are continuous distribution and discrete distribution

Continuous distribution : Single continuous distribution

                  Fixed partition allocation

                  Dynamic partition allocation

 

Single continuous distribution : Memory is divided into system areas , User area . For single user , Single task operating system

Fixed partition allocation : The user memory space is divided into several fixed size regions

                        There are two cases of equal size and unequal size between partitions

                        data structure : Section number , Partition size , Partition start address , Partition status

Dynamic partition allocation : The system initially has only one free area . When a process requests space , According to the size of space needed by the process, the system divides a free area to the process .

                       
  When running for a period of time , Because some processes will be released , So there are discontinuous free areas in memory . So when the process requests memory again , The system finds a suitable size of free area from all the idle areas for allocation . The size and number of partitions in the system vary , The size and number of free areas also vary .

 

The system needs to establish and maintain records of idle partitions , It is represented by free partition and free partition chain

Free partition table

data structure : Section number , Partition size , Partition start address

Idle partition chain

data structure : Free partition size , Starting address of free partition , Pointer to the previous free partition , Pointer to the next free partition

 

Dynamic partition allocation algorithm :

First fit algorithm : The first adaptation algorithm requires that the idle partition chain be linked in the order of increasing address . During memory allocation , Search in sequence from the beginning of the chain , Until we find one                      
        Until there are free partitions that can meet the process size requirements .

Cyclic first adaptation algorithm : It is also linked in the order of increasing address . When allocating memory space for a process , No longer looking for the appropriate free partition from the beginning of the chain every time , It's from the top                      
            The next free partition of the free area found the next time starts the search .

Best fit algorithm : All the free partitions are formed into a free zone chain in the order of increasing partition size . Each time the partition size is found to be close to the needs of the process, the memory space is large                      
      Small

 

Discrete distribution : Paging storage management

                  Segmented storage management

                  Segmented Paged Memory Management

Paging storage management : Page table is the data structure established by the system for the process , From page table ( Logical address ) To page box ( Physical address ) Mapping of .

Segmented storage management : The address space of a process is divided into segments , The system allocates a continuous area of physical memory for each segment , Different segments can be placed in the                      
      Different areas of physical memory .

Segmented Paged Memory Management : The logical space of user process is divided into several segments , Each segment is further divided into several pages . Processes are stored in physical memory in units of pages                        
            discharge , The discrete pages in each segment have logical relevance .

 

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