This variable is for use only on VAX/VMS systems. When it is set to 1 (on, true, yes), it causes the runtime to specify a key type for numeric keys. In order to make use of this variable, you must also create XFD files at compile-time (-Fx), and you must set the configuration variable XFD_DIRECTORY to point to the directory containing those XFD files.
When these steps have been taken, the runtime will create RMS files with keys having either the packed decimal or integer attribute, under certain conditions dictated by the RMS file system. In particular, a key will have the packed decimal or integer attribute only if it is a single-segment key and only if there is a single field in the key. In this case, a USAGE COMP-3 data item in the key will receive the packed decimal attribute, and a USAGE COMP-5 data item (if it is 2, 4, or 8 bytes long) will receive the integer attribute.
One effect of having this attribute set on key fields is that the order of the data is changed. Without this attribute, a file that has records with keys -3, -2, -1, 0, 1, 2, 3 would have those records ordered in this way: 0, 1, -1, 2, -2, 3, -3. With this attribute, those records would be ordered in this way: -3, -2, -1, 0, 1, 2, 3. The default setting for this variable is 0 (off, false, no).