Fan speed control is achieved by accessing some features available in some hardware monitor
chip or some other special hardware. These chips might be able to
controls fan speeds. They usually do this by using PWM output. A PWM
is a digital signal that alternates some levels very fast, thus simulating some
intermediate average level. The net result is a perceived average voltage lower than the usual one.
Please note that some chips (very few of them) are able to lower the voltage without PWM simulation.
The fans, on the other hand, can report their speeds (RPM) by using some internal sensors that
report how often some current flows between two plates. Fans are built assuming nominal voltages
and a continuous signal. When voltages are lowered or modulated through PWM, some fans are no
longer able to properly trigger when those plates face each other and resulting fan speeds may
show odd values. SpeedFan works flawlessly even in such situations.
To find your CPU's temperature sensor you can leave your system idle for a few minutes, to let
temperatures drop, and then go to 100% usage for a while. The temperature that rises faster
is the one you're searching for. Other available temperature readings usually come from your
sensor chip itself, from the southbridge, the voltage regulator, or even
from an additional probe placed under the processor. This additional temperature sensor is not
necessarily a duplicate. Some CPUs are not actually able to report the internal temperature from
their die. To be able to read their temperatures, an additional external sensor (thermocouple) is
used. In such cases, you will see two temperatures referring to the processor. The
higher of the two is from the die. As a final note, please remember that not all available
temperature sensors are actually connected to something. If you happen to read unusually high or low
temps, they are likely to be from a disconnected (unused) temperature sensor.
Hardware sensor chips are generic devices that can be used to measure voltages from anywhere.
The measured voltage must be converted to the range required by the sensor chip. Standard
monitoring chips specify which external circuitry must be used in order to measure voltages
outside some range. Voltages like 12V, -5V, -12V and some others need this external circuitry.
Some manufacturers chose not to follow datasheets. If this is your case, then you will read
unusual values from SpeedFan. Since this custom circuitry is not known, SpeedFan does not
try to "guess" it as any reading wouldn't be safe. If you get really odd voltage readings,
simply enter configuration and uncheck the relevant ones.
This can occasionally happen if you have an nVidia video card and you are using some software
combination. Due to the lack of documentation, the only option is to use the /NONVIDIAI2C
command line switch when running SpeedFan. You can find further info about it in
S.M.A.R.T. (or SMART) is a technology built into recent hard disks. If enabled, it lets the end
user query the hard drive about its health and, eventually, performances. The end user (you) can
access such info by using some specific software. SpeedFan can query those info for you.
SMART reports, for example, if the hard disk has been used for too much time (thus reaching its
expected end of life), or if it took too many attempts to start spinning, or even if too many
read errors occurred. About every modern hard disk can report its temperature this way. They do
have a temperature sensor that might be located inside the enclosure or somewhere outside it.
Please, note that SF might inform you that a reboot is needed in order to support SMART on your PC.
I asked for datasheets to some manufacturers, but with slow or no answer at all. Anyhow: since
version 3.00 I'm ready to, easily, add support for new chips. I've got several chips to add. I
will start adding detection for them: if you will get a message saying "PLEASE REPORT", please
contact me and I will add support for it in a few days :-)
Even though the sensor chip might be able to change fan speeds, the hardware manufacturer
still has to include some external circuitry. This is not always included. I'm able
to know if a motherboard can change fan speeds, but not if it is unable for sure. You might try to
contact the hardware manufacturer and let me know.
There are several ways to label available readings (temperatures, voltages, fan speeds). The first source
should be the BIOS. Enter BIOS at boot, write down labels and readings and compare them to those reported
by SpeedFan. You can use manufacturer's custom hardware monitors to match readings too. SpeedFan strictly
adheres to available datasheets for each sensor chip. Please remember that hardware monitors chips have
some pins (small connectors) that should be connected to some additional hardware (temperature probes,
thermistors or thermocouples) in order to be able to read temperatures. Only a few hardware monitor
chips do label their connectors with "CPU", "System" and the like. Most of them use labels like "Temp1",
"Local" or "Remote". Hardware manufacturers connect available pins to different temperature sensors
basically according to the physical placement of components on the motherboard. This means that the same
chip, an ITE IT8712F, for example, might be connected to a sensor diode measuring CPU temperature on Temp2
and, on a different hardware, it might be connected on Temp1. If you have a "Local" sensor and a "Remote"
labeled one, this usually means that "Local" is the temperature of the monitor chip itself and "Remote"
is the temperature read from a "remote" probe. When you have properly identified which temperature sensor
is which, try to lower the speed of each fan and look at reported speed and temperatures. This way you can
match PWM controls (speeds) with fans. Please, note that if you do not allow SpeedFan to change any fan
speed and set all the speeds too low, then SpeedFan won't be able to avoid overheating.