The datacenter tiers are a well-known four tier system that provides a simple and effective means for identifying different data center site infrastructure design topologies. The Uptime Institute's tiered classification system is an industry standard approach to site infrastructure functionality addresses common benchmarking standard needs.

The most common tier for commerical datacenters is Tier 3. For government datacenters, Tier 4 is usually preferred. The four tiers, as classified by The Uptime Institute include the following:

NOTE: The difference between 99.982% and 99.995%, 0.013%, while seemingly nominal, it could be significant depending on the application. Looking at one (1) year or 525,600 minutes, T3 will be unavailable 94.608 minutes whereas T4 will only be unavailable 26.28 minutes. Therefore, T4 in a year will be available for 68.328 more minutes than T3. One can only imagine how many more credit cards transactions can take place when the services are run by a T4 as opposed to a T3 center. Finally, when one considers T3 vs. T2, one would find T3 designed to be 22.6 hrs more available than T2.