Windows上的“剩余时间”估计值有时足以让任何人发疯，但你有没有想过Windows是如何决定这些时间的？今天的超级用户问答帖子对一个好奇却又沮丧的读者问题给出了一些答案。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

Windows 8.1文件传输窗口截图由im really famecore提供。

问题

超级用户读者“im really famecore”想知道Windows如何确定对文件执行操作所需的时间：

I wanted to know if there is an equation that Windows uses to determine how long it takes to perform an action with a file such as: deleting, copying, erasing, or installing.

For example, when I delete a file and Windows says Time remaining: 18 seconds, how is it calculating this number, and what does it use to calculate it?

Windows是使用一个特殊的公式来确定执行操作所需的剩余时间，还是仅仅提供了一个“最佳猜测”的估计？

答案

超级用户贡献者valmikyarquissandas和Richard为我们提供了答案。首先，Valmiky Arquissandas：

Have you noticed that it usually does not give you any estimates during the first few seconds?

That is because during the first few seconds, it just does the operation it has to do. Then, after a short amount of time, it knows how much it has already copied/deleted/etc, and how long it took. That gives you the average speed of the operation.

Then, divide the remaining bytes by the speed, and you have the time it will take to complete the operation.

This is elementary school math. If you want to travel 360 km, and at the end of the first minute you have traveled 1 km, how long will it take you to reach your destination?

Well, the speed is 1 km/minute, so that is 60 km/hour. 360 km divided by 60 km/hour gives you an estimated time of 6 hours (or 360 km / 1 km/minute = 360 minutes = 6 hours). Since you have already traveled for one minute, then the estimated time left is 5 hours and 59 minutes.

Substitute travel with copy, km with bytes, and that answers your question.

Different systems have different ways of estimating time. You can take the last minute and the estimates may vary wildly. Or you can take the full time, and if the speed actually changes permanently, your estimates may be far removed from reality. What I described is the simplest method.

接着是理查德的回答：

If you are interested, this question tells you how Windows and OSX formats the time left into the progress bar once it has an idea how long it has remaining.

When shortening time expressi*** in progress dialogs, should they be rounded up or down?

Raymond Chen, a developer on the Windows team at Microsoft, confirms this algorithm (see Valmiky’s answer above) in a posting on his blog. He also explains why it can be wrong.

Why does the copy dialog give such horrible estimates?

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