Yes, but only on the early Macs. PowerPC Macs that use DDR1 ram cannot have their ram overclocked. Only those with PC-66 through PC-133 can have their ram overclocked. Also when overclocking the ram, the CPU's clock speed increases as well unless its multiplier is changed for the new ram speed. Also note, overclocking the ram through OpenFirmware does not work. It only changes what the computer reports the speed as being. To overclock it you must solder resisters on it's board.