Swedish Chess Computer Association (SSDF) is the longest running rating list in existence. Its origins can be traced to 1979 as a subscription group for a computer chess magazine called PLY. In 1984, the SSDF was formally founded, with the purpose "to coordinate the interest for computerchess and chesscomputers in Sweden, and to release PLY". The first public rating list was published in PLY in that year. A history of the SSDF can be found here.
The time control is 40 moves/2 hours, followed by 20 moves/hour. Each chess program uses a separate computer (connected by auto232 cable) and its own book.
The SSDF's method of testing most closely mimics the conditions humans play under. It is the only list that compares dedicated chess computers, older DOS programs, newer programs, and programs played older and newer processors all together. It also has made some effort to calibrate its Elo ratings to human ratings.
The list lacks relevance nowdays. Very few of the newer programs have been tested by the SSDF. The method of testing requires alot of resources and hinders the group from providing statistically significant data in a timely manner.