Unlimited hosting is impossible. Many hosts use the term “unlimited” as a sales technique, although technically they cannot provide “unlimited” hosting.

What they mean is unmetered, where there are no software-created limits; there are however, hardware limits. Of course, as a client you rarely know the hardware limits, but they are always existent. There is no such thing as an “unlimited” hard drive, and as such there's no such thing as “unlimited” disk space. The same applies for network connections and “unlimited” bandwidth.