Tyan Computer GX21 - Manual (Page 77)

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Delay Prior to Thermal
This BIOS feature is only valid for systems that are powered
by 0.13µ Intel Pentium 4 processors with 512KB L2 cache.
These processors come with a Thermal Monitor which con-
sists of an on-die thermal sensor and a Thermal Control Cir-
cuit (TCC).
When the Thermal Monitor is in automatic mode and the ther-
mal sensor detects that the processor has reached its maxi-
mum safe operating temperature, it will activate the TCC. The
TCC will then modulate the clock cycles by inserting null
cycles, typically at a rate of 50-70% of the total number of
clock cycles. This results in the processor "resting" for 50-
70% of the time.
As the die temperature drops, the TCC will gradually reduce
the number of null cycles until no more is required to keep the
die temperature below the safe point. Then the thermal sen-
sor turns the TCC off. This mechanism allows the processor
to dynamically adjust its duty cycles to ensure its die temper-
ature remains within safe limits.
The Delay Prior To Thermal BIOS feature controls the activa-
tion of the Thermal Monitor's automatic mode. It allows you to
determine when the Pentium 4's Thermal Monitor should be
activated in automatic mode after the system boots. For
example, with the default value of 16 Minutes, the BIOS acti-
vates the Thermal Monitor in automatic mode 16 minutes
after the system starts booting up.
Generally, the Thermal Monitor should not be activated
immediately on booting as the processor will be under a
heavy load during the booting process. This causes a sharp
rise in die temperature from its cold state. Because it takes
time for the thermal output to radiate from the die to the heat
sink, the thermal sensor will register the sudden spike in die
temperature and prematurely activate the TCC. This unnec-
essarily reduces the processor's performance during the
booting up process.
Therefore, to ensure optimal booting performance, the activa-
tion of the Thermal Monitor must be delayed for a set period
of time.
It is recommended that you set this BIOS feature to the low-
est value (in minutes) that exceeds the time it takes to fully