Or how to install programs on multiple disks?
1 Answer
You cannot really change installation path as unixes use a fixed file system hierarchy. To understand the file system layout in elementary OS you can see https://askubuntu.com/questions/138547/how-to-understand-the-ubuntu-file-system-layout (Ubuntu and elementary OS share the same layout).
As of installing on multiple disks, you can mount them as part of your file system.
apt
? Needs clarification