"ISAMA" is the name for A-Shell's implementation of ISAM PLUS file system. It is based on a commercial third-party ISAM product called D-ISAM, which in turn is an upward-compatible version of the Informix C-ISAM library.

Using the third-party library meant that we could not provide compatibility with ISAM PLUS at the binary file level, although files can be easily converted using the ISMUTL dump and load operations. But it did allow us to maintain BASIC source and RUN compatibility with virtually all of the ISAM PLUS language statements. In addition, the commercial library is very fast and robust, and supports a number of additional features which give it several advantages over the AMOS version. The following several topics provide additional details about programming with ISAM-A, including differences between the AMOS (ISAM PLUS) and A-Shell (ISAM-A) versions, extensions, and a reference to the language statements.