An ad server is a type of server used to store and deliver online advertising to websites. The server can store material for a single company's websites, in the case of a local server, or it can be used to deliver advertising to a variety of clients spanning the Internet, in a remote server. Ad servers also have other capabilities, including capacity for collecting and storing user data, monitoring clickthroughs, and other activities. Numerous companies offer remote ad server capabilities to sites interested in running ads and design local servers for companies that want to control their own advertising.
The ad server is dedicated solely to advertising matters. It stores ads in a variety of sizes and styles for different applications, including banner ads and interstitial advertisements. The ad server can also store video and audio advertising, along with animated ads. When someone lands on a website connected to the server, a request is sent and an advertisement is returned. The ads change as people navigate the site, as dynamic advertising of this style allows for more exposure to different advertisers.
An ad server may be capable of tailoring ads to specific users. It can track referrals, habits on a website or family of websites, the content on a page, and so forth to deliver ads it thinks will be most relevant. Someone who spends a lot of time on the cooking section of a newspaper's website, for example, might get ads for grocery stores, culinary suppliers, and so forth. Ad servers also collect data about who clicks through and track things like how long people stay on individual pages, as well as a website as a whole.
The smarter the ad server, the more expensive it tends to be, as more work is needed to maintain it. Many sites interested in running advertisements don't have the level of support needed to generate and serve ads in-house, and prefer to join an ad network. The network uses an ad server to deliver ads, usually offering some degree of control so people can delist ads not relevant to their users. In exchange for ad placement, it offers a small fee per click or on another basis. Usually, the larger the website, the better the compensation from advertisers, as people will pay a premium for ad placement on heavily trafficked sites.
Redundancy is common with ad servers, to make sure delivery of advertisements is smooth and reliable. The servers are constantly updated with new ads and algorithms to keep them current and functional.