Shulou(Shulou.com)06/01 Report--

Memory masking

In the late computer bits and pieces, the main memory capacity is very small, although there is only one user program in the main memory, but the storage space can not hold the user process often occurs, this contradiction can be dealt with with masking techniques.

The fundamental idea of the cover-up is that because the program does not have to visit all parts of the program and data at any time (especially large programs), the user space can be distributed to a fixed area and several masking areas. The often lively part is placed in the fixed area, and the other parts are segmented according to the misappropriation relationship. First of all, put those sections that will be visited into the cover area, and the other sections in external memory, and transfer them into the cover area in bits and pieces before the demand is misappropriated, and exchange the Huaxia section of the cover area.

The characteristic of the concealment technique is that it breaks the restriction that all the information of a process must be loaded into main memory before dry operation, but it still cannot run when the amount of code of the program running at the same time is larger than that of main memory.

Memory communication

The basic idea of communication (exchange) is to move the program in the waiting form (or deprived of the right to run under the CPU adjustment criterion) from memory to secondary storage, freeing up memory space, which is also called swapping out; the process of moving programs ready to compete for CPU operation from secondary memory to memory, this process is also called swapping. The intermediate adjustment introduced in Chapter 2 is the use of communication skills.

For example, there is a multiprogramming case in which CPU uses the Kongfu slice rotation adjustment algorithm. When the time slice arrives, the memory manager swaps out the process that has just been performed, and swaps another process into the memory space that has just been released. At the same time, the CPU tuner can dispatch worker slices to other processes that are already in memory. Each process communicates with another process with a finished husband's film. In fantasy situations, the communication process of the memory manager is fast enough that there is always a process that can be performed in memory.

Regarding communication needs, pay attention to the following achievements:

Exchange demand backup storage, on weekdays is fast disk. It must be large enough and provide direct access to these memory images.

In order to use CPU ineffectively, it is required that the implementation time of each process is longer than the communication time, and the secondary influence on the communication time is the transfer time. The transfer time is inversely proportional to the memory space being communicated.

If the process is replaced, it is necessary to ensure that the process is completely in the form of leisure.

Communication space is usually used as a whole disk and relied on piecemeal files, so it can be used very quickly.

Communication usually starts when there are many processes running and memory space is tight, while piecemeal load drops.

Popular communication is rarely used, but some variants of communication strategies still play a role in many bits and pieces (such as UNIX bits and pieces).

Communication skills are mainly stopped between divergent processes (or homework), while masking is used to unify a program or process. Because the concealment technique requests to give the concealment structure between the program segments, so it is not clear to the user and the programmer, so with regard to the contradiction that the main memory can not store the user program, the ancient operation bits and pieces are handled by the virtual memory technique. concealment skills have become history, while communication skills still have strong vitality in ancient operation bits and pieces.

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