When we document something in the real world, we make permanent, immutable records of it. But computer documents are volatile, ephemeral constellations of data. Sometimes (as when you’ve just opened or saved them) the document as portrayed in the window is identical to what is stored, under the same name, in a file on the disk, but other times (as when you have made changes without saving them) it is completely different. In any case, every time you hit “Save” you annihilate the previous version of the “document” and replace it with whatever happens to be in the window at the moment. So even the word “save” is being used in a sense that is grotesquely misleading – “destroy one version, save another” would be more accurate.
Neal Stephenson, from In the beginning…was the command line