A central ad server is a server that stores advertisement and delivers them to web site visitors. These servers centrally store the ads so that advertisers can track from one source the distribution of their online advertisements, and have one location for controlling the rotation and distribution of their advertisements across the world wide web. The central ad server was first developed and introduced by FocaLink Media Services in 1995 for controlling online advertising or banner ads. The company was founded by Dave Zinman and Jason Strober, and based in Palo Alto, CA. In 1998, the company changed its name to AdKnowledge, and was eventually purchased by CMGI in 1999.