CPU fans are not completely universal. Different CPUs and motherboards have specific requirements and compatibility issues. The size and mounting mechanism of CPU fans vary. For example, there are common sizes like 40mm, 60mm, 80mm, 92mm, 120mm, and 140mm. The mounting holes on the motherboard for attaching the fan also differ. Some motherboards use a standard Intel or AMD mounting pattern, but there are also proprietary mounting systems. So, a fan designed for one type of motherboard may not fit another.

The power requirements and control capabilities of CPUs and motherboards play a role too. Some CPUs generate more heat and require more powerful fans with higher airflow and static pressure. Additionally, the connection interface between the fan and the motherboard matters. While many modern fans use a 3-pin or 4-pin connector, older systems may have different types. A fan with a 4-pin PWM connector may not work optimally with a motherboard that only supports 3-pin connectors in terms of speed control. Moreover, the height of the fan and the clearance above the CPU is important. In some small form factor cases or systems with large heatsinks or other components near the CPU socket, a taller fan may not fit. So, when choosing a CPU fan, it is essential to consider the specific model of the CPU, the motherboard's features and layout, and the overall system configuration to ensure proper fit, functionality, and cooling performance.