What is a data center? Do two servers in a closet count as a data center?Terminology affects perception, so defining our terms carefully helps organize our thoughts. So how do we define the term \u201cdata center\u201d?One of the features of Google that I really enjoy using is the \u201cdefine:\u201d modifier. If you try a search for \u201cdefine: data center\u201d in Google you will get a set of definitions from the Web. Google seems to use an algorithm to determine when a segment of text in a Web page defines a term, perhaps by looking for the term followed by a colon and some sentence.Here are some of the definitions for \u201cdata center\u201d:* A physical structure, usually a stand-alone building, that is designed to house a multiplicity of computers.* An institutionally supported facility providing convenient access to, manipulation of, and\/or distribution of data sets (including supporting information and expertise) for a wide community of users. It has a long-term charter (not tied to the lifetime of a specific project).* A facility that provides storage and management of server, network and computer equipment.* A facility used for housing a large amount of electronic equipment, typically computers and communications equipment.The above definitions are a starting point, but they tend to be biased to one or other perspective of the data center. Some see the building primarily; other definitions are focused on the servers, some on the organizational structure.In this newsletter, we provided an enumeration of the key disciplines within a data center, focusing on the people and the skills we see in a data center: computing, networking, storage, facilities, management\/operations and security (the last two as horizontal overlays across the first four).As we conduct interviews with IT executives for our upcoming research benchmark on data centers we\u2019re asking for definitions of \u201cdata center.\u201d We are trying to find the common elements upon which everyone can agree. So far we have: \u201cAn environmentally controlled centralized facility providing business services by securely delivering applications and data across a network to remote users.\u201dAnother important aspect of the data center definition has to do with the level of redundancy and availability designed into the facility. Clearly a dedicated stand-alone bunker with redundant\/uninterruptible everything is not the same as a basement computer room. The Uptime Institute provides a commonly accepted classification of the data center according to the level of availability designed into the facility. It defines four tiers (Tier-I has the lowest availability, Tier-IV the highest) with fairly precise classification metrics.If you have a different perspective or a better definition, please send us e-mail. We would love to hear your feedback.