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1、在软件体系中，位于最上层的是应用程序，比如我们平常使用的浏览器，播放器，qq等，从整个层次结构来看，开发工具与应用程序属于同一个层次，因为它们都使用一个接口，即操作系统应用程序编程接口（Application Programming Interface）。应用程序接口的提供者是运行库，什么样的运行库提供什么样的API，比如Linux下单Glibc库提供POSIX的API；Windows 的

A process is a program in execution. A process is more than the program code, which is sometimes known as the text section. It also includes the current activity, as represented by the value of the

In UNIX, as we’ve seen, each process is identified by its process identifier,which is a unique integer. A new process is created by the fork() system call. The new process consists of a copy of the

有多个线程在操作时,如果系统只有一个CPU,则它根本不可能真正同时进行一个以上的线程,它只能把CPU运行时间划分成若干个时间段,再将时间段分配给各个线程执行,在一个时间段的线程代码运行时,其它线程处于挂起状态.这种方式我们称之为并发(Concurrent).       当系统有一个以上CPU时,则线程的操作有可能非并发.当一个CPU执行一个线程时,另一个CPU可以执行另一个线程,两个线程互不

1. Multiprogramming system provide an environment in which the various resources(like CPU,memory,and peripheral devices) are utilized effectively,but they do not provide for user interaction with

1.hierarchical storage structure     This notion of inserting a smaller, faster storage device (e.g., cache memory)between the processor and a larger slower device (e.g., main memory) turns outt