CPU OPT is a 4-pin header on a motherboard that is used as a secondary connection for cooling fans. It is an optional header used for large PC heatsinks or to connect AIO cooling pumps. Unlike the CPU FAN header, it doesnt have integrated safeguards, so it does not affect the system booting. Even if the CPU OPT header is empty, your system will work normally. In the case of your system getting hot, it will provide you with a warning of the system being overheated. The purpose of CPU OPT is to power the other cooling systems associated with the CPU cooler. With CPU OPT, you can use splitters to channel the power to multiple devices. CPU OPT is mainly used when you have more than one fan on your cooler/radiator, and you need someplace to plug it in. Most AIO/liquid cooling solutions can also use it as a power source for water-cooling pumps and other things that might require power but is not important or power-hungry enough to reroute power directly from the power supply. CPU FAN, on the other hand, is the primary fan connection and has a direct connection to BIOS. It directly affects the system boot, and the system will not boot unless a fan is connected to it. The CPU_FAN header is where you plug the fan, and it is important bec...