SpeedFan 4.44 introduced a new and improved fan control strategy. Let us first recall some concepts and definitions:
any computer can have any number of fans, from 0 up.
On a specific computer, SpeedFan might be able to read fan speed RPMs (Revolutions Per Minute). SpeedFan might not be able to read the RPMs of all installed fans. If SpeedFan can read no RPM, check for future SpeedFan releases as hardware support improves over time.
On a specific computer, SpeedFan might be able to access SPEED controls (usually referred to as PWMs). If you would like to know more about PWM, feel free to read this article. Please note that RPM readings and PWM settings are not necessarily tied together. The hardware monitor chips located inside computers have some wires to read fan speeds and some others to control PWMs. It is up to the computer manufacturer to decide whether and how to connect those wires. Understanding which SPEED (PWM) acts (controls) which fan can be a matter of trial and error, but it is worth the effort.
Every fan reacts to PWM control differently. 4-wire fans usually exhibit a rather linear response. 3-wire fans can be much less linear. It depends on several factors, including the circuitry on the motherboard and the type of fan used.