The banners are downloaded from the exchange. A monitor on the exchange determines, from [referer|referral information] supplied by web browsers, how many times a member web site has displayed the banner advertisements of other members, and credits that member with a number of displays of its banner on some other member's web site. Link exchanges usually operate on a 2:1 ratio, such that for every two times a member shows a second member's banner advertisement, that second member displays the first member's banner advertisement. This page impressions:credits ratio is the exchange rate.
One of the earliest link exchanges was LinkExchange, a company that is now owned by Microsoft.
Link exchanges have advantages and disadvantages from the point of view of those using the World Wide Web for marketing. On the one hand, they have the advantages of bringing in a highly targeted readership (for link exchanges where all members of the exchange have similar web sites), of increasing the "link popularity" of a site with Web search engines, and of being relatively stable methods of hyperlinking. On the other hand, they have the disadvantages of potentially distracting visitors away to other sites before they have fully explored the site that the original link was on.
Feig notes several aspects of link exchange companies that prospective members take into account: