A turbocharger consists of a compressor wheel and exhaust gas turbine wheel coupled together by a solid shaft and that is used to boost the intake air pressure of an internal combustion engine. The exhaust gas turbine extracts energy from the exhaust gas and uses it to drive the compressor and overcome friction. In most automotive-type applications, both the compressor and turbine wheel are of the radial flow type. Some applications, such as medium- and low- speed diesel engines, can use an axial flow turbine wheel instead of a radial flow turbine.

With the exception of some large turbochargers for low-speed engines, the bearings that support the shaft are usually located between the wheels in an overhung position. This flexible rotor design ensures that the turbocharger will operate above its first, and possibly second, critical speeds and can therefore be subject to rotor dynamic conditions such as whirl and synchronous vibration.