DDR3 - Cycle Time

Clock Cycle time is the reciprocal of the base clock frequency.

DDR3-1066 = 266MHz base clock, or 3.75ns per cycle.
DDR3-1333 = 333MHz base clock, or 3.00ns per cycle.
DDR3-1600 = 400MHz base clock, or 2.50ns per cycle.
DDR3-2000 = 500MHz base clock, or 2.00ns per cycle

example: 1/266E10^6

equals 3.75nS