All ISAM 1.x now use the same implementation. Previously, traditional ISAM 1.0 files with 3 level, 512 block indexes used an old implementation, while files with more levels or larger index blocks used the new implementation. The purpose of the bifurcation was to eliminate the possibility that the ISAM 1.1 improvements—variable index levels and block size—might introduce bugs in stable code. But the new implementation has been proven solid in the field for over a year, other than issues with 2GB and 4GB limits, which is well beyond what the ISAM 1.0 format could have handled in the first place. Also, in the process of recent testing, many tests have been added to the code to detect index anomalies that previously may have gone undetected. So the new implementation is simply better, even for files too small to benefit from the variable index configurations.
