There are not many changes between version 1.4 and 1.5. The C-sources have been cleaned and comments have been updated. The stack memory management based on using the MMU has been changed to run on a number of System-V Unix systems offering shared memory. Handling dates has been changed. All functions handling dates now return a floating point number, expressing the time in seconds since January 1, 1970. A predicate convert_time/8 is available to get the year, month, etc. The predicate time/6 has been deleted. get_time/1 and convert_time/8 together do the same.
From version 1.5, the system is distributed in source form, rather than in object form as used with previous releases. This allows users to port SWI-Prolog to new machines, extend and improve the system. If you want your changes to be incorporated in the next release, please indicate all changes using a C-preprocessor flag and send complete source files back to me. Difference listings are of no use, as I generally won't have exactly the same version around.