计算机网络 与 分布式系统 的区别与联系

　　The key distinction is that in a distributed system, a collection of independent computers appears to its users as a single coherent system. Usually, it has a single model or paradigm that it presents to the users. Often a layer of software on top of the operating system, called middleware, is responsible for implementing this model. A well-known example of a distributed system is the World Wide Web. It runs on top of the Internet and presents a model in which everything looks like a document (Web page). In a computer network, this coherence, model, and software are absent. Users are exposed to the actual machines, without any attempt by the system to make the machines look and act in a coherent way. If the  achines have different hardware and different operating systems, that is fully visible to the users. If a user wants to run a program on a remote machine, he has to log onto that machine and run it there.
　　In effect, a distributed system is a software system built on top of a network. The software gives it a high degree of cohesiveness and transparency. Thus, the distinction between a network and a distributed system lies with the software (especially the operating system), rather than with the hardware. Nevertheless, there is considerable overlap between the two subjects. For example, both distributed systems and computer networks need to move files around. The difference lies in who invokes the movement, the system or the user.

--Computer Networks, 5th Edition P2

	Difference	Connection
Distributed System	Appears as a single coherent system. A layer of software on top of the operating system, called middleware, is responsible for implementing this coherent system. e.g. the World Wide Web.	A distributed system is a software systems built on top of a network. The software gives it high degree of cohesiveness and transparency.
Computer Networks	No system making the machines look and act in a coherent way.  e.g. users log onto the machine to run programs on the machine.