Many modern motherboards don't expose fan RPM data through standard SMBus or ACPI interfaces.
SIW relies on hardware monitoring chips, such as ITE, Winbond, and Nuvoton, but if the BIOS doesn't publish those values, SIW can't display them.
If fans are powered directly from the PSU, via Molex or SATA, or through a hub without tachometer feedback, SIW won't see RPM data.
Fans must provide tachometer feedback through a compatible motherboard header or controller for their speed to be reported.
Some newer Super I/O chips require updated detection routines.
If SIW doesn't yet support that specific chip, fan speeds won't be shown.
Certain vendors lock down sensor access, allowing only their proprietary utilities, such as ASUS AI Suite or MSI Dragon Center, to read fan RPM.
Fans spinning below a threshold, such as 200 RPM, or locked at a fixed speed may not report values, so SIW shows nothing.