>>By the way, my guess is that a Word or Excel file hardly has the chance to become fragmented because the whole is done in a single write, so there is virtually no chance for something else to intrude while it is written.
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>I think a Word or Excel file can very well become fragmented, because the available free space isn't necessarily contiguous. The missing piece of information for me, however, is: how does the operating system decide where to start writing the file? The first available cluster perhaps? That is a possibility, but I can also imagine several alternative algorithms.

Same for me, actually. I favour that file systems too have smartened over the years, and that now they look for a fitting contiguous chunk first and going to chunkS only when that fails. Admitted a guess (wish?).

Here's something else that figures into all this thinking...

Consider a system with only Word running, no network connection. Allow that 'safety' is turned on in Word, at every 5 minutes.
So the document is loaded from HD. Let's assume that, as soon as the first keystroke is done in that document the first 'safety' backup is done. When, 5 minutes later, the 'safety' backup is done (again) it is likely that, for at least an instant, there sit 3 copies on the HD (the original, the first safety and the last safety).
The first safety is deleted promptly as the last is completed successfully. The author keeps typing and soon another 5 minutes elapses, requiring the next 'safety'. At this time there is a good chance that this next safety fits nicely in the first safety's space, so it is written there and the second safety's space is freed. Now assume that the author, within 2-3 more minutes, closes the document, making a final Save. That Save will have a good chance to be where the second safety had been written, then the original and the last safety can be freed. So we end up with the document now sitting far from where it originally sat and with lots of free clusters between its old place and the new one. Makes for possible mashed-up free space quite quickly, I would think.

cheers

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>Hilmar.