Ruby 1.6.0 included a new version of the standard date library, written by Tadayoshi Funaba. This is the ancestral version of the current standard date library.
It stored the date as a julian day integer. It supported a modifiable date of calendar reform, where the ruby 1.0 version had a static date of calendar reform.
Like the ruby 1.0 code, the ruby 1.6.0 code can also be run directly on 1.8, where it is about 2/3 the speed of the 1.0 code.
Both the 1.0 code and the 1.6.0 code only handle dates, they do not handle datetimes.