And this is because as you start writing--saving files to your hard drive, what happens is you might save this file here, then this one, then this one, then this one, but very reasonably you might go back eventually and delete this one.

这是因为当你开始对硬盘驱动器进行读写时,你可以保存一个文件到磁盘的某处，然后再一个，再一个，又一个，最后你可能回到这,并删除这一个文件。

哈佛公开课 - 计算机科学课程节选