The Cache Manager fetches and caches files from File Server machines on behalf of application programs that are running on client machines. To locate a file to be retrieved, it first contacts the Fileset Location Server (FL Server) to learn the location of the fileset that houses the file; to retrieve the file, it then contacts the File Server machine that houses the file. The File Exporter on the File Server machine delivers the file, which the Cache Manager stores in the client machine's cache, which is an area of local disk or memory designated for temporary storage. Once the data is cached locally, the Cache Manager can access it as quickly as it can a local file.
The Cache Manager verifies that its cached files match the central copies at File Server machines by keeping the tokens that the File Exporters send with the files. A token acts as the File Exporter's promise to contact the Cache Manager if the centrally stored copy of a file changes while the Cache Manager has a cached copy. If the central copy changes, the File Exporter revokes the token; the Cache Manager sees that the token is revoked and retrieves the new version of the file when an application program next requests data from it.
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