PSE 2020 folder structure

Currently BOTH the catalog and pictures reside on the hard drive (1 TB), and when I do a "back up the catalog" operation from within PSE it of course includes both, so I want to be clear on your terminology of what constitutes the "catalog".

The word 'catalog' used in image management softwares clearly matches the common use. A catalog of the paintings of Le Louvre museum does not contain the canvases themselves but all the information and indexes about those paintings and their location in the various rooms as well as small images (= thumbnails). However, in the Organizer, Adobe covers both the catalog and the media trees when dealing with backups. Of course it's important to induce beginners to think about backing up both catalogs and media, but the word is indeed misleading here. I'd prefer to call the media trees : 'library', but I am not a native English speaker...

If your catalog and library both reside on the external drive, that can't be the default installation choice. As explained before, that's the situation when you restore a backup (which contains both types of assets) to a new destination computer, drive, partition or even master folder. Remember you can move or copy the catalog folder in custom location from the Explorer. Moving it does not alter the links in the database.

One clarification, please. When you refer to the CATALOG in the context of your answer and its location, do you mean ONLY the database and not the actual pictures files?

Yes, we generally refer to the catalog as the folder containing the database files, not the media (photo and video files) that are referred to by the database.  Although they can both be on the same drive, they don't have to be.  The folder looks something like this:

Also, when I try to rename the current catalog (because calling it a 9.0 catalog is not descriptive any longer) it says it can't rename it because it is in use in another program. Appparently it thinks I still have an old version installed, which I do not. How to I get around this renaming problem?

The catalog is open in the Organizer.  That's why you can't rename it.  You can  open another catalog - create a new dummy one if you only have one catalog. You will then be able to rename the original.  Or, you can rename the catalog folder in Windows Explorer.  Once you have renamed the folder, double-click on the catalog.pseXXdb file, as suggested by Michel, and the renamed catalog will open in the Organizer.

The main help doc for catalogs is in the online help:

https://helpx.adobe.com/in/elements-organizer/user-guide.html/in/elements-organizer/using/creating-editing-catalogs.ug.html

To answer your question more precisely, since PSE6, the catalog folders are subfolders of a hidden folder under

ProgramData

   Adobe

       Elements Organizer

          Catalogs

Simply remember to use the menu Help >> System Info to get the precise location for your Win or Mac PSEversion.

What you have to know is that the default location is not mandatory. You can move or copy a given catalog folder from the explorer to a 'custom' destination of your choice. There are a number of reasons you may prefer a 'custom' location:

- to save space on a small SSD C: master drive

- to store your media file tree with the catalog on an external drive to share between several computers alternatively.

- to create kinds of backups for the catalog only

-  ...

When you migrate to a new computer via the usual full backup and restore procedure, you may decide to store your image folder tree on a different folder than the default 'Pictures' system file. I recommend creating a new master folder with due permissions just under the root drive of the internal or external drive. In the restore to custom location, the catalog folder is also restored under your custom master folder. The catalog manager has the choice to 'move' the catalog back to default location. It can't move from default to custom, you need to do that from the Explorer.

Once a catalog has been moved, the shortest way to start it is to double click on the file 'catalog.pseXXdb' in the catalog folder. This starts the organizer with that catalog and that location is remembered.