there was originally some controversy over whether the unix time_t should be signed or unsigned. If unsigned, its range in the future would be doubled, postponing the 32-bit overflow (by 68 years). However, it would then be incapable of representing times prior to 1970. Dennis ritchie, when asked about this issue, said that he hadn't thought very deeply about it, but was of the opinion that the ability to represent all times within his lifetime would be nice. (ritchie's birth, in 1941, is around unix time −893,400,000.) the consensus is for time_t to be signed, and this is the usual practice.