SpeedFan is a free hardware monitoring and fan control program for Windows. It reads temperatures, fan speeds and voltages from supported components, then uses temperature readings to regulate compatible fans. The connection between those readings and the fan controls is configurable, so one fan can respond to heat reported by several sensors.
Sensor readings
SpeedFan searches for hardware monitoring chips and digital temperature sensors, including those on supported motherboards, some graphics cards and hard disks. Its main window brings their readings together, showing temperature values alongside fan rotation speeds and voltage measurements. You can rename detected readings to identify the components they represent.
The Charts tab plots selected readings over time. You choose which sensors the chart displays. Separate colors distinguish the selected traces on the graph.
Reading a fan’s speed and controlling it are separate capabilities. A motherboard may expose an RPM reading without providing a usable speed-control connection. SpeedFan can regulate a fan only when the monitoring hardware, motherboard circuitry and fan connection allow it.
Fan curves
An advanced fan controller connects a PWM output—the hardware signal that controls fan speed—to one or more temperature sources. For each source, you define a response curve that assigns a control percentage to different temperatures. This allows a gradual response to rising heat instead of using one fixed fan setting.
When several temperatures control the same output, SpeedFan can use the highest requested speed or add the requested speeds together. Each source keeps its own curve, allowing a shared fan to respond differently to heat from different components. Below or above a curve’s temperature range, the corresponding endpoint setting remains in effect.
Hysteresis controls how quickly the fan slows after a temperature falls. A higher temperature applies its new setting immediately; on the way down, SpeedFan retains the existing setting until the temperature has fallen by the configured amount. This reduces repeated speed changes around a temperature boundary.
Minimum and maximum control values bound the result of the curves. A separate warning threshold takes priority: if a linked temperature exceeds that level, SpeedFan commands full speed for the relevant output. Automatic Fan Speed enables temperature-driven control, while a separate option selects the advanced curve method. Simpler control settings also let you associate temperatures with fans and define their operating range.
Hard disk SMART attributes
SpeedFan also reads internal status information from supported EIDE, SATA and SCSI hard disks. For SMART-capable drives, selecting a disk displays its reported attributes, including current and worst values, warning thresholds and raw data. Depending on the drive, these can include temperature, power-on activity, read errors or sectors replaced with spare ones.
The fitness and performance indicators summarize different groups of drive attributes. Fitness draws on health-related attributes, while performance uses those marked as performance-related. These summaries are estimates based on the information returned by the disk. Manufacturers choose the attributes and their scales, so the detailed values and thresholds remain relevant when interpreting the result.
