The Tier Model for Mission Critical Facilities, created and governed by The Uptime Institute (TUI), is the most pervasively referenced data center tier model. It is not the only multi-level model describing the quality of data center facilities, but it by far enjoys the majority of mindshare in this regard.
The four-tier model from The Uptime Institute was developed through thoughtful analysis and extensive empirical data from facilities of member organizations. Quality control over interpretation and accreditation of tier ratings to facilities is closely guarded by TUI. Awarding a tier level to a facility can only be done through designated professional services suppliers sanctioned by TUI. Self proclaimed use of a tier rating by any company without TUI involvement exposes the firm to legal action by TUI. Even so, misuse and misappropriation by enterprises world-wide is prolific.