That depends on the motherboard and the fan header available for population with a 3pin fan. Some boards come with an option to set a 4pin fan header (outside of the CPU_Fan header) to either be voltage regulated or PWM.
Thus my subsequent inquiry about what your motherboard's make and model is...? Please include the make and model of your fan/fans as well.
MERGED QUESTION Question from armagedon3009 : "4pin fan conected to 3pin conector on mb"
can i control this in bios like low medium and high speed if u understandt me