The Quadra series of Apple Computers were the high end series that
replaced the Mac II series. They introduced in 1991 and intended for
professionals and businesses. There was the Quadra 700 and then the
900 with a CPU speed of 25 MHZ.
Apple Centris computers were introduced briefly in 1993 as a mid-range computer to fit in between the LC low cost computers and the Quadras high end computers. Computers in this series were the Centris 610, 650 and 660AV.