How to keep iTunes from installing on primary drive?

I don't understand how iTunes works when installing. During the installatin process I directed the installation to the E: drive to keep my fast C: drive clutter free. The folder Apple installed on the E: drive is a whopping 186MB and the space iTunes consumed on the main C: drive is a MASSIVE 15.4GB <-- that's 15.4Gig's......... All the software updates, all the backups, the logs, the syncs are all stored on the C drive. Why? and how can I change it?