Toshiba NB520 - Manual (Page 65)

Heat dispersal
To protect against overheating, the processor is equipped with an internal
temperature sensor which activates a cooling fan or lowers the processing
speed if the computer's internal temperature rises to a certain level. You
are able to select whether to control this temperature by either turning on
the fan first, then if necessary lowering the processor speed, or by lowering
the processor speed first, then if necessary turning on the fan. Both of
these functions are controlled through the Power Options.
When the processor's temperature falls within normal range, the fan will be
turned off and the processor operation returned to its standard speed.
If the processor's temperature reaches an unacceptably high level with
either setting, the computer automatically shuts down to prevent any
damage. In this instance all unsaved data in memory will be lost.
NB520 series
User's Manual 3-31