THE G-EXEC 'G-STAR' FILE FORMAT
The G-EXEC data file format, also known as the 'G-STAR file', was a random access binary file, with fixed record lengths, containing a file header followed by data records.
The file header specified field names, field types (numeric or alpha), file lengths for alpha fields, and absent data codes separately for each field. These were stored row-wise. The record length of each file was defined by the maximum space required by the file header records or the data records, and thus was different for every file.
This required a file index (or directory, or catalogue) to be used before a file could be accessed, as the Fortran random access file open command needs the record length to be specified. This was one of the factors dictating the structure of the G-EXEC system, with two-pass processing in which the first pass accessed the file index to determine the record lengths of all files required, and created a batch job to be run in a second pass.
The file structure is shown below: