By the way, you might be thinking, "well, data core is only one letter less than index file, but it very much matters what those letters are. In "index file", the presence of three thin letters together — fil — creates a practical ligature, which means that it can be hard to distinguish between those letters — especially if you have to decrease the kern, or "smash the letters together".
Effectively, we really can't do a lower case version of the logo because of this pseudo-ligature.
With "data core", you've got nice, rounded letters bumping up against each other that will be distinct even if you decrease the kern to the point that the letters actually overlap.
I know it may seem silly and nitpicky, but data core opens up so many graphical possibilities that index file precludes.