Introduction
14 Thermal and Mechanical Design Guidelines
1.3 Definition of Terms
Term Description
ACPI Advanced Configuration and Power Interface.
BTX Balanced Technology Extended
Bypass
Bypass is the area between a passive heatsink and any object that can act
to form a duct. For this example, it can be expressed as a dimension away
from the outside dimension of the fins to the nearest surface.
DTS
Digital Thermal Sensor: Processor die sensor temperature defined as an
offset from the onset of PROCHOT#.
FSC
Fan Speed Control: Thermal solution that includes a variable fan speed
which is driven by a PWM signal and uses the digital thermal sensor as a
reference to change the duty cycle of the PWM signal.
Health Monitor
Component
Any standalone or integrated component that is capable of reading the
processor temperature and providing the PWM signal to the 4 pin fan
header.
IHS
Integrated Heat Spreader: a thermally conductive lid integrated into a
processor package to improve heat transfer to a thermal solution through
heat spreading.
LGA775 Socket
The surface mount socket designed to accept the processors in the 775–
Land LGA package.
P
MAX
The maximum power dissipated by a semiconductor component.
PWM
Pulse width modulation is a method of controlling a variable speed fan. The
enabled 4 wire fans use the PWM duty cycle % from the fan speed
controller to modulate the fan speed.
T
A
The measured ambient temperature locally surrounding the processor. The
ambient temperature should be measured just upstream of a passive
heatsink or at the fan inlet for an active heatsink.
T
C
The case temperature of the processor, measured at the geometric center
of the topside of the IHS.
TCC
Thermal Control Circuit: Thermal Monitor uses the TCC to reduce die
temperature by lowering effective processor frequency when the die
temperature has exceeded its operating limits.
T
C-MAX
The maximum case temperature as specified in a component specification.
T
CONTROL
T
CONTROL
is the specification limit for use with the digital thermal sensor.
T
CONTROL_BASE
Constant from the processor datasheet that is added to the T
CONTROL_OFFSET
that results in the value for T
CONTROL
T
CONTROL_OFFSET
Value read by the BIOS from a processor MSR and added to the
T
CONTROL_BASE
that results in the value for T
CONTROL
T
DIODE
Temperature reported from the on-die thermal diode.
TDP
Thermal Design Power: A power dissipation target based on worst-case
applications. Thermal solutions should be designed to dissipate the thermal
design power.
T
E
The ambient air temperature external to a system chassis. This
temperature is usually measured at the chassis air inlets.
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