# 并发和并行的区别

1. 并发（concurrency）：指宏观上看起来两个程序在同时运行，比如说在单核cpu上的多任务。但是从微观上看两个程序的指令是交织着运行的，指令之间交错执行，在单个周期内只运行了一个指令。这种并发并不能提高计算机的性能，只能提高效率（如降低某个进程的相应时间）。
2. 并行（parallelism）：指严格物理意义上的同时运行，比如多核cpu，两个程序分别运行在两个核上，两者之间互不影响，单个周期内每个程序都运行了自己的指令，也就是运行了两条指令。这样说来并行的确提高了计算机的效率。所以现在的cpu都是往多核方面发展。


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