写译 — 并行和并发的区别是什么？

• Author : Cyan_RA9
• 和大家分享英语写译，包括计算机英文教材，计算机基础，中英文诗词，英文名著，日常对话等，每一篇文章 我都会分别给出“原文内容”，“第一版翻译” 和 “第二版翻译”，以及“生词整理”共四部分。
• 写译 — 并行和并发有什么区别？

【原文内容】

• 并行：是指在计算机系统中同一时刻有多个程序在同时运行，称这些在同一时刻同时运行的程序是并行执行的。
• 并发：是指在计算机系统中一段时间内宏观上有多个程序在同时运行，但同一时刻只有一个程序在运行。在单处理器系统上，宏观来看这些程序是同时向前推进的；微观来看并发执行的程序是交替在处理机上运行的。在多处理器系统上，每个处理器都可以实现并发，且不同处理器上的多个程序是并行执行的。
• 并行是并发的特例，程序有并行性则一定是并发的，反之并发活动不一定是并行执行的。并行性是指两个或多个事件在同一时刻发生；并发性是指两个或多个事件在同一时间间隔内发生，但同一时刻只有一个事件在发生。
• 实际上并发性是一种设计思想，即要尽可能复用计算机中的资源来提高计算机系统的运行效率。eg：当正在执行的程序要执行I/O操作时，操作系统就会要求其让出处理器资源使其他程序能上处理器运行，使I/O设备可以与处理器并行工作，减少了硬件资源相互等待带来的时间损耗。
• 程序并发性体现在两个方面：
  1. 用户程序和用户程序之间的并发执行。
  2. 用户程序与操作系统程序之间的并发执行。

【第一版翻译：（润色前，手译）】

• PARALLELISM : means that within computer systems there are several programs functioning simultaneously at the same instant, and we call these programs parallel-executed.
• CONCURRENCY : means that within computer systems there are several programs executing simultaneously in the same duration from a macro view but there is only one program executing at the same instant.In a Uniprocessor System, these programs seem to be executing forward simultaneously from a macro view but actually these simultaneous-executed programs are functioning alternately in the processor from a micro view. In a multiprocessor System, every single processor has the ability to fulfill Concurrency, and different programs in different processors are parallel-executed.
• Parallelism is a exception from Concurrency so a program must has the characteristic of Concurrency provided it has the feature of Parallelism, instead Concurrent activities won't be absolutely parallel-executed. Parallelism means that two or more events happen at the same instant; Concurrency means that two or more events happen at the same duration but there is only one event happening at the same instant.
• Actually Concurrency is more likely a kind of design concept, namely reusing resources within computer as much as possible to enhance the functioning efficiency of computer system. eg: when a currently executing program want to exert I/O operations, Operating System will order it to relinquish processor resource to ensure that other programs can take the processor and execute, enabling I/O devices work in parallel with processor and then reducing the time cost caused by the mutual waiting from different hardware resources.
• The Concurrency of programs embodies in two major aspects:
  1. Concurrent-Executing between the user program and the user program.
  2. Concurrent-executing between the user program and the OS programs.

【第二版翻译：（润色后，雅思水准）】

• PARALLELISM : refers to multiple programs running simultaneously at the same instant within a computer system, such programs are termed parallel-executing.
• CONCURRENCY : refers to a state where multiple programs appear to execute simultaneously over a given period macroscopically yet only one program runs at any given instant.In a Uniprocessor System, these programs seem to be executing forward simultaneously macroscopically but actually these simultaneous-executing programs are functioning alternately on the processor microscopically. In a multiprocessor System, every single processor supports Concurrency, and different programs across distinct processors execute in parallel.
• Parallelism constitutes a subset of Concurrency so a program inherently has the characteristic of Concurrency provided it has the feature of Parallelism, whereas not all Concurrent activities are parallel. Parallelism means that two or more events happen at the same instant; Concurrency means that two or more events happen at the same duration but there is only one event happening at the same instant.
• Actually Concurrency is more likely a kind of design philosophy, namely reusing resources within computer as much as possible to enhance the functioning efficiency of computer system. For instance, when an executing program initiates I/O operations, Operating System preempts its processor allocation to ensure that other programs can take the processor and execute, enabling I/O devices work in parallel with processor and then reducing the time cost caused by the mutual waiting from different hardware resources.
• Program Concurrency manifests in two dimensions:
  1. Concurrent-Executing between the user program and the user program.
  2. Concurrent-executing between the user program and the OS programs.

【生词整理】

• Parallelism：n.并行性，平行，相似，排比
• refer to：phrase.指的是，涉及，查阅，参考
• parallel-executing：adj.并行执行的
• at the same instant：phrase.同一时刻
• at any given instant：phrase.同一时刻
• over a given period：phrase.一段时间内
• macroscopically：adv.宏观上，宏观地
• microscopically：adv.微观上，微观地
• constitute a subset of...：phrase.是......的子集，是......的特例

【写译手稿】