"A search appliance is a dedicated computer with a small
footprint (1U or 2U) whose only task in life is to provide indexing
and searching services to your users or customers. All appliances
ship with a web-based interface for easy administration and
end-user document search and retrieval. Most search appliance
manufacturers provide multiple appliance levels to fit your budget
or specific indexing needs. This list of seven enterprise search
appliances is in no particular order.
"A word of caution is in order when comparing search appliances
and their pricing models. Most appliance vendors charge by how many
documents you want to index. A few charge by the amount of data
you're indexing, while others have no limit on the number of
documents or the data volume."