SpeedFan is a freeware program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. SpeedFan can even access S.M.A.R.T. info for those hard disks that support this feature and show hard disk temperatures too, if supported. SpeedFan supports EIDE, SATA and SCSI disks. SpeedFan can even change the FSB on some hardware (but this should be considered a bonus feature).

At the lowest level, SpeedFan is an hardware monitor software that can access temperature sensors, but its main feature is that it can control fan speeds (depending on the capabilities of your sensor chip and your hardware) according to the temperatures inside your pc, thus reducing noise and power consumption. Several sensors, like Winbond's and the AS99127F support fan speed changing, as well as others from Maxim, Myson, Analog Devices, National Semiconductor and ITE, but the hardware manufacturer must have connected the relevant pins to some additional, yet trivial, circuitry. This means that if you have, say, a Winbond W83782D on a BP6 then you're ok, but not every motherboard with such an hardware monitor chip will be able to change fan speeds.

SpeedFan can find almost any hardware monitor chip connected to the 2-wire SMBus (System Management Bus, a subset of the I2C BUS) Serial Interface and to the ISA BUS. SpeedFan works fine with Windows 9x, ME, NT, 2000, 2003 and Windows XP. SpeedFan can be minimized to the tray and is compatible with Motherboard Monitor 5.

SpeedFan can:

• handle almost any number of South Bridges
• handle almost any number of hardware monitor chips
• handle almost any number of temperature readings
• handle almost any number of voltage readings
• handle almost any number of fan speed readings
• handle almost any number of PWMs

4.28 - New Features

• added IN-DEPTH HARD DISK ONLINE ANALYSIS tool
• added centralized INTERNET configuration tab in CONFIG dialog
• added support for NForce410
• added support for new video cards
• added Temperature Sensor Type, BJT Offset and Gain support for Fintek F75375S in CONFIGURE / ADVANCED (on Asus V9999 you might need to set BJT OFFSET from 174 to 202)
• SMART overall indicators are computed using a more advanced strategy
• updated the help file
• properly fixed byte swapped HDD model names

More screenshots can be viewed here.