分布式计算

昂宿星团人

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来源：http://en.wikipedia.org/wiki/Distributed_computing
鹅群维基：http://www.equn.com/wiki/%E5%88% ... F%E8%AE%A1%E7%AE%97

Introduction
The word distributed in terms such as "distributed system", "distributed programming", and "distributed algorithm" originally referred to computer networks where individual computers were physically distributed within some geographical area. The terms are nowadays used in a much wider sense, even when referring to autonomous processes that run on the same physical computer and interact with each other by message passing.
引言
“分布式的（distributed ）”这个词在诸如分布式系统（distributed system）、分布式编程（distributed programming）、分布式运算法则（distributed algorithm）等术语中原本指的是由多台个人计算机物理地分布在一定地理区域中而形成的的计算机网络。这些术语如今被赋予了更加宽泛的意义，甚至可以指代运行在同一台计算机上，并通过传递信息互相影响的几个进程。

While there is no single definition of a distributed system, the following defining properties are commonly used:
*There are several autonomous computational entities, each of which has its own local memory.
*The entities communicate with each other by message passing.
由于分布式系统没有规范的定义，我们可以用一下特性来区别分布式系统：
*有多个自主的计算实体（computational entities），并且各自拥有本地存储器。
*计算实体间通过消息传递进行联系。

In this article, the computational entities are called computers or nodes.
A distributed system may have a common goal, such as solving a large computational problem. Alternatively, each computer may have its own user with individual needs, and the purpose of the distributed system is to coordinate the use of shared resources or provide communication services to the users.
本文中，计算实体也会被写作“计算机（computers）”或“节点（nodes）”。
一个分布式系统应有一个共同目标，比如解决一个需要大量计算的问题。或者，每台计算机都有其使用者，这些使用者有着各自不同的需求，而分布式系统的目的就是合理调度分享的资源或给用户提供交流服务。


Other typical properties of distributed systems include the following:
*The system has to tolerate failures in individual computers.
*The structure of the system (network topology, network latency, number of computers) is not known in advance, the system may consist of different kinds of computers and *network links, and the system may change during the execution of a distributed program.
*Each computer has only a limited, incomplete view of the system. Each computer may know only one part of the input.
另外几个分布式系统的典型特性是：
*系统必须容纳个体计算机返回的错误
*系统的结构（网络拓扑结构、网络延迟、计算机编号等）是不能够预测的，系统可能包含有不同种的计算机和网络连接，并且会在分布式程序进行过程中出现变化。
*每台计算机都只能受限制地观察到不完整的系统。有可能每台计算机都只知道受处理信息的一部分。

昂宿星团人

Parallel or distributed computing?
The terms "concurrent computing", "parallel computing", and "distributed computing" have a lot of overlap, and no clear distinction exists between them. The same system may be characterised both as "parallel" and "distributed"; the processors in a typical distributed system run concurrently in parallel. Parallel computing may be seen as a particular tightly-coupled form of distributed computing, and distributed computing may be seen as a loosely-coupled form of parallel computing. Nevertheless, it is possible to roughly classify concurrent systems as "parallel" or "distributed" using the following criteria:
并行计算还是分布式计算？
术语“并存计算（concurrent computing）”，“并行计算（parallel computing）”和“分布式计算（distributed computing）”有许多共同点，且没有特别明确的区别。同一个系统可能同时被特指为“并行的（parallel）”和“分布式的（distributed）”；一个典型的分布式系统中的各处理器是以并行的形式运作的。并行计算也可能以分布式计算的一种密集的形式出现，而分布式计算也可能以并行计算的一种较松散的形式出现。不过，我们可利用下列标准粗略地将“并行系统”与“分布式系统”区分开：


In parallel computing, all processors have access to a shared memory. Shared memory can be used to exchange information between processors.
In distributed computing, each processor has its own private memory (distributed memory). Information is exchanged by passing messages between the processors.
并行计算中，所有的处理器共享内存。共享的内存可以让多个处理器彼此交换信息。
在分布式计算中，每个处理器都有其独享的内存（分布式内存）。数据交换通过处理器传递信息完成。


The figure on the right illustrates the difference between distributed and parallel systems. Figure (a) is a schematic view of a typical distributed system; as usual, the system is represented as a graph in which each node (vertex) is a computer and each edge (line between two nodes) is a communication link. Figure (b) shows the same distributed system in more detail: each computer has its own local memory, and information can be exchanged only by passing messages from one node to another by using the available communication links. Figure (c) shows a parallel system in which each processor has a direct access to a shared memory.
右边的示意图说明了分布式系统与并行系统的差异。图a是典型的分布式系统的图示；通常，系统被表示成一种用节点（顶点）代表计算机、直线代表计算机连接的图。图b描述的是同一个分布式系统的更加详细的信息：每台计算机都有各自的本地内存（memory），并且只通过节点间的可用通信连接交换数据。图c是一个各处理器都（processor）连接到同一个共享内存的并行系统。


The situation is further complicated by the traditional uses of the terms parallel and distributed algorithm that do not quite match the above definitions of parallel and distributed systems; see the section Theoretical foundations below for more detailed discussion. Nevertheless, as a rule of thumb, high-performance parallel computation in a shared-memory multiprocessor uses parallel algorithms while the coordination of a large-scale distributed system uses distributed algorithms.
相比而言，“并行算法”和“分布式算法”这两个术语在传统用法中的地位就复杂多了。他们并不十分符合上面提到的阐释；下文中的“理论基础”部分将对此进行详细讨论。不过一般来说，在多处理器共享内存的高效并行计算中使用并行算法，而用来协调大规模分布式系统则使用分布式算法。

Youth

建议不要在wiki上放这个的翻译，因为这个分布式计算的含义比我们这的志愿计算（虽然也被叫做分布式计算）范围要宽广多了，混在一起更说不清楚

或者把原来错误使用分布布计算的场合都修正过来，然后分布式计算是分布式计算，志愿计算是志愿计算

昂宿星团人

回复 3# Youth


    那可是大工程嘞。。那还有必要翻译下去不？

Youth

我把这个转到wiki版，看看大家的意见吧

昂宿星团人

回复 5# Youth


    那么此页面的翻译工作先暂停咯

昂宿星团人

话说。。咱有这么冷么