Updating data is not supported by this isam
Once a file is loaded data records are not moved; inserted records are placed into a separate overflow area.
To locate a record by key the indexes on disk are searched by a complex self-modifying channel program.
I am trying to update data in a text file (with bound controls...) and I get an error message "Updating Data in a linked table not supported by this ISAM" Double Dutch to me... Once you've finished editing write the data back to the file - it's a bit crass I know but it's the only way I've found of doing it so far (this would be a single user solution). The cylinder index stores the highest key on a cylinder, and the disk address of the corresponding track index.An optional master index, usually used only for large files, contains the highest key on a cylinder index track and the disk address of that cylinder index.ISAM was replaced at IBM with a methodology called VSAM (virtual storage access method).Still later, IBM developed DB2 which, as of 2004, IBM promotes as their primary database management system. The Open VMS operating system uses the Files-11 file system in conjunction with RMS (Record Management Services).