51
个编辑
更改
→Comparison with real machines
5. Turing machines describe algorithms independent of how much memory they use. There is a limit to the memory possessed by any current machine, but this limit can rise arbitrarily in time. Turing machines allow us to make statements about algorithms which will (theoretically) hold forever, regardless of advances in conventional computing machine architecture.
5. Turing machines describe algorithms independent of how much memory they use. There is a limit to the memory possessed by any current machine, but this limit can rise arbitrarily in time. Turing machines allow us to make statements about algorithms which will (theoretically) hold forever, regardless of advances in conventional computing machine architecture.
图灵机描述的算法与它们使用多少内存无关。当前任何一台机器所拥有的内存都是有限制的，但这个限度可以随着时间的推移而任意上升。图灵机让我们可以对算法做出（理论上）永恒的陈述，无论传统计算机架构如何进步。
# Turing machines simplify the statement of algorithms. Algorithms running on Turing-equivalent abstract machines are usually more general than their counterparts running on real machines, because they have arbitrary-precision data types available and never have to deal with unexpected conditions (including, but not limited to, running [[out of memory]]).
# Turing machines simplify the statement of algorithms. Algorithms running on Turing-equivalent abstract machines are usually more general than their counterparts running on real machines, because they have arbitrary-precision data types available and never have to deal with unexpected conditions (including, but not limited to, running [[out of memory]]).
Another limitation of Turing machines is that they do not model concurrency well. For example, there is a bound on the size of integer that can be computed by an always-halting nondeterministic Turing machine starting on a blank tape. (See article on unbounded nondeterminism.) By contrast, there are always-halting concurrent systems with no inputs that can compute an integer of unbounded size. (A process can be created with local storage that is initialized with a count of 0 that concurrently sends itself both a stop and a go message. When it receives a go message, it increments its count by 1 and sends itself a go message. When it receives a stop message, it stops with an unbounded number in its local storage.)
Another limitation of Turing machines is that they do not model concurrency well. For example, there is a bound on the size of integer that can be computed by an always-halting nondeterministic Turing machine starting on a blank tape. (See article on unbounded nondeterminism.) By contrast, there are always-halting concurrent systems with no inputs that can compute an integer of unbounded size. (A process can be created with local storage that is initialized with a count of 0 that concurrently sends itself both a stop and a go message. When it receives a go message, it increments its count by 1 and sends itself a go message. When it receives a stop message, it stops with an unbounded number in its local storage.)
图灵机的另一个局限性是它们不能很好地模拟并发性。例如，可以由始终停止的非确定型图灵机从空白磁带上开始计算整数大小的界限。(见关于无界非决定论的文章)相比之下，有一些没有输入的总是停止的并发系统可以计算无界大小的整数。(可以用本地存储创建一个进程，这个进程的初始化计数为0，它同时给自己发送一个停止和继续的消息。当它收到一个继续消息时，它将自己的计数增加1，并给自己发送一个继续消息。当它收到停止消息时，它在本地存储中以一个无限制的数字停止）。)
图灵机的另一个局限性是它们不能很好地模拟并发性。例如，可以由始终停止的非确定型图灵机从空白磁带上开始计算整数大小的界限。(见关于无界不可判定论的文章)相比之下，有一些没有输入的总是停止的并发系统可以计算无界大小的整数。(可以用本地存储创建一个进程，这个进程的初始化计数为0，它同时给自己发送一个停止和继续的消息。当它收到一个继续消息时，它将自己的计数增加1，并给自己发送一个继续消息。当它收到停止消息时，它在本地存储中以一个无限制的数字停止）。)
====Interaction====
====Interaction====
自20世纪70年代以来，计算机的交互式使用变得更加普遍。原则上，可以通过让外部代理与图灵机同时从磁带中读出并写入磁带的方式进行建模，但这很少与交互的实际发生方式相吻合；因此，在描述交互性时，通常首选I/O自动机等替代程序。
自20世纪70年代以来，计算机的交互式使用变得更加普遍。原则上，可以通过让外部代理与图灵机同时从磁带中读出并写入磁带的方式进行建模，但这很少与交互的实际发生方式相吻合；因此，在描述交互性时，通常首选I/O自动机等替代程序。
==History==
==History==