@Emile S Thumbs.db holds the images icons preview (as jpg) for images, I do not know for folders(also invisible file).
That file is not mandatory, it is created when the folder is viewed as Icons AND some images exists in that folder.
That one still doesn't suit my needs, sorry. If I create a picture file, I know Windows would create the thumbnail automatically; If I create another kind of file, the Thumbs.db file isn't to be modified. In both cases, dealing with this file is probably not a good thing.
@Emile S On OS X, there is also another invisible file whose name holds MacOS or so.
Sorry, I don't quite understand this statement… What do you mean by “holding MacOS”?
@Emile S BTW: you are right for the item icons… it probably is stored in the index file (name forgotten) where items are stored.
You're talking about the catalog of the file system? That's possible, as I guess a custom icon isn't stored in the file itself (otherwise, I couldn't have a “0 byte” file with a custom icon; and I actually can). Still, how to set it?
@Emile S When the Finder does not display correctly that file, it is because the file is corrupted. In the old times, it was possible to ask the Finder to rebuild this file, but I never knew how to do that in macOS X…
Right. In Mac OS 9 (and earlier), there were the “Desktop DB” and “Desktop DF” files; those could be rebuilt (using option+command keys at the end of the start up process, IIRC). Unless I'm mistaken, they didn't contain file icons, but your choices to open files with “other” applications and other “desktop services” information. I don't think they contained file icons, otherwise those files would have been way bigger (and searching inside a single file for a particular file's icon would have been a pain for the OS, anyway).
Mac OS X doesn't use those files anymore. .DS_store files provide a subset of these ones, I believe.
@Emile S Some big wig asked for changes… like so many things (some were not for the best).
I couldn't agree more. If changes could be made only because technology progresses (and not because an OS maker just decides to remove a feature because he doesn't like that feature himself…), we would not have to learn a ton of new things for the sake of change.
@Emile S Nota: I counted 21 items (files and folders) in the hard disk root folder.
Possibly. What's your point here?
@Emile S I think it will be faster to search the informaton in what was was called Inside Mac: Files (20 years ago or so); actual name unknow.
Faster, probably. Accurate, not so sure…