> not requiring installation

It's a strange quirk of Windows that when you install a new piece of software, it will ask you in the wizard where you want to store it (C: drive or D: drive). D: is usually an external hard-drive, and so I select that. But the D: drive can magically become the E: drive in some cases when you have other media inserted like an SD card. So this is why I prefer portability since the path is agnostic and portable software doesn't care about drive letters.