The Reference Desk/What powers the TARDIS?

In some episodes of the new series, it's said that it's the Time Vortex (The Parting of Ways). Then, in The Doctor's Wife, it's called the Matrix. But in Journey to the Centre of the TARDIS, it's said that the Eye of Harmony powers the TARDIS.

So, which is it...or, if it is all three, what is the relationship between them?