The search application in MOSS 2007 can index a large amount of data quickly and provide search services to thousands of users.
The search engine used in the search application is designed to be extensible and programmable for customization of the search service. The search engine program crawls and indexes the information, similar to the Microsoft Windows Desktop Search Engine.
The search service architecture consists of content sources, index service, query service, and search center.
Content sources include the data to be indexed.
Index service indexes the content sources. To speed up indexing, you can use multiple indexing services. The index results, also known as index catalog, are copied to one or more servers running the query service.
The query service accepts search requests and returns results. To increase search capacity, you can configure multiple query services in a load-balanced cluster. All query services in a load-balanced cluster must have copies of the same index catalog from an index service. Each query service accepts an index catalog from only one index service.
The Search Center is the user interface used for submitting search queries. You can configure the Search Center to submit queries to multiple query services and then display the results of the query in separate tabs.
The modular architecture makes the search application highly scalable. In a small environment, you can run all search components on a single server. To increase scalability, you can host the search components on dedicated servers.
Self Service SharePoint 