The CPU_FAN and SYS_FAN utilize standard 4-pin PWM layouts, but Lenovo's onboard diagnostic firmware expects specific RPM feedback telemetry. Standard retail fans may generate a "Fan Error" warning message during POST, forcing you to press F1 to bypass the warning at startup. Complete Front Panel Pinout Guide ( F_PANEL )
Standard retail motherboards use a 24-pin ATX connector. The IS6XM features a proprietary 4-pin CPU power and a 14-pin main ATX power connector . Lenovo Is6xm Rev 1.0 Motherboard Manual