Microsoft KB Archive/32424

Indexed (ISAM) File Format

PSS ID Number: Q32424 Article last modified on 04-21-1993

3.00 MS-DOS

Summary: In Microsoft COBOL Version 3.0, Indexed files consist of a data (.DAT) file and an index (.IDX) file. The .DAT file has the structure of a variable-format Sequential file, even when fixed format is requested. If the data file is used without the index, it may be accessed as a variable-format Sequential file. Please note the following: 1. Records in the .DAT file are not in any particular sequence. 2. There are a number of “System Records” in the .DAT file that are ignored when processed as a variable-format Sequential file. 3. The .IDX file is of variable format. However, the header information reflects the .DAT file contents. The recording mode flag in the header of the index reflects the requested format of the file. The recording mode flag in the header is the only difference between fixed and variable .IDX files.

Additional reference words: 3.00 Copyright Microsoft Corporation 1993.