> 2. A lot of my editing involves editing near (but not at) the end of
> a file. I assume (I know) that the software that saves the file is
> smart enough not to rewrite the entire file but instead to preserve
> the beginning of the file and just rewrite the changed part of the
> file (or from there to the end of the file).
Not completely sure if "you assume" or "you know" it to be the case.
Especially given that you then add:
> Can anyone confirm that,
which suggest you're not really sure (unless it referred to something else).
Let's say you are using vi. Last I heard, it will buffer the entire file contents on the initial open (unless you use the right option etc). How about on file write?
I don't know.
I submit that rather than try to figure out each app, just install sar and related utilities and view the aggregate throughput. Maybe use cacti for quicker-to-screen graphics if you want.