1.4.2.6. - The Index File
Indexing a long ASCII data file to find at what byte offset each scan begins takes time. Once scans.4 has indexed a file, it saves the index information in a binary-format index file. The name of the index file is formed by appending .I to the original data-file name. As long as the index file is more recent than the data file, scans.4 will take the index information from the index file.