Riva 128 (April 1997) to TNT (June 15, 1998) took 14 months, TNT2 (March 15, 1999) 8 month, GF256 (October 11, 1999) 7 months, GF2 (April 26, 2000) 6 months, | 3dfx dies here |, GF3 (February 27, 2001) 9 months, GF4 (February 6, 2002) 12 months, FX (March 2003) 13 months, etc ...
Nvidia had an army of hardware engineers always working on 2 future products in parallel, 3dfx had few people in a room.