OS02进程描述-2014-2015-2讲解.ppt

操作系统为了管理进程和资源，必须掌握关于每个进程和资源当前状态的信息。普遍使用的方法 是：操作系统构造和维护它所管理的每个实体的信息表。 If the OS is to manage processes and resources, it must have information about the current status of each process and resource. The universal approach to providing this information is straightforward: The OS constructs and maintains tables of information about each entity that it is managing. A general idea of the scope of this effort is indicated in Figure 3.11 , which shows four different types of tables maintained by the OS: memory, I/O, file, and process. Although the details will differ from one OS to another, fundamentally, all operating systems maintain information in these four categories. Figure 3.11 depicts the structure of the location information in the following way. There is a primary process table with one entry for each process. Each entry contains, at least, a pointer to a process image. If the process image contains multiple blocks, this information is contained directly in the primary process table or is available by cross-reference to entries in memory tables. Of course, this depiction is generic; a particular OS will have its own way of organizing the location information. Memory tables are used to keep track of both main (real) and secondary (virtual) memory. Some of main memory is reserved for use by the OS; the remainder is available for use by processes. Processes are maintained on secondary memory using some sort of virtual memory or simple swapping mechanism. The memory tables must include the following information: ? The allocation of main memory to processes ? The allocation of secondary memory to processes Any protection attributes of blocks of main or virtual memory, such as which processes may access certain shared memory regions ? Any information needed to manage virtual memory * From this simple model, we can already begin to appreciate some of the design elements of the OS. Each process must be represented in some way so that the OS can keep track of it. Th