SpeedFan is a freeware program that monitors fan speeds, temperatures and voltages in computers with hardware monitoring 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 can even change the FSB on some motherboards (but this should be considered a bonus feature). At the lowest level, SpeedFan is an hardware monitoring software, but its main feature is that it can control the speed of the fans (depending on the capabilities of your sensor chip and your hardware) according to the temperatures inside your pc, thus reducing noise and power consumption. SpeedFan can be a good tool to build a silent PC, with an overall low dbA emission. Several sensors, like Winbond's and ASUS AS99127F support fan speed changing, as well as others from MAXIM, MYSON, ANALOG DEVICES, NATIONAL SEMICONDUCTORS and ITE, but the motherboard manufacturer must have connected the relevant pins to some additional, yet trivial, circuitry. This means that if you have, say, a W83782D on a BP6 then you're ok, but not every motherboard with such an hardware monitoring chip will be able to change fan speeds.
SpeedFan can find almost any hardware monitoring chip connected to the SMBus (a subset of the I2C BUS), to the ISA BUS and to nVidia Video Cards. SpeedFan works fine with Win9x, WinME, WinNT, Win2k, Win2K3 and WinXP.
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