For large old-style ISAM files (not ISMA-A) you can now achieve much better performance by increasing the IDX block size and/or number of index levels (from the previous fixed values of 512 and 3). New versions of the ISMBLD and ISMDMP utilities allow access to the new capability.
Existing files remain completely compatible and will perform exactly as before. This is also true of new files that continue to use the old default values of 512 for the block size and 3 levels.
To take advantage of the new capabilities, you must dump the file and build a new one with the new ISMBLD switches /B:# and /L:# (see below).
