Page 84 - A Practical Guide from Design Planning to Manufacturing

60 Chapter Two

In 2004, motherboards using the Balanced Technology Extended
(BTX) standard began appearing. This new standard is incompatible
with ATX and requires new cases although it does use the same power
supply connectors. The biggest change with the BTX standard is rear-
ranging the placement of the components on the board to allow for
improved cooling. When the ATX standard first came into use, the cool-
ing of the components on the motherboard was not a serious consider-
ation. As processor power increased, large heavy heat sinks with
dedicated fans became required.
More recently, chipsets and graphics cards have begun requiring their
own heat sinks and fans. The performance possible from these compo-
nents can be limited by the system’s ability to cool them, and adding
more fans or running the fans at higher speed may quickly create an
unacceptable level of noise.
The BTX standard lines up the processor, chipset, and graphics card,
so air drawn in from a single fan at the front of the system travels in a
straight path over all these components and out the back of the system.
This allows fewer total fans and slower fan speeds, making BTX systems
quieter than ATX systems providing the same level of cooling. Like ATX,
the different BTX standards are compatible, with cases designed for one
BTX board accommodating any smaller BTX size.
Processor performance can be limited not only by the ability to pull heat
out but also by the ability of the motherboard to deliver power into the
processor. The power supply of the case converts the AC voltage of a wall
socket to standard DC voltages: 3.3, 5, and 12 V. However, the processor
itself may require a different voltage. The motherboard Voltage Regulator
(VR) converts the standard DC voltages into the needed processor voltage.
Early motherboards required switches to be set to determine the volt-
age delivered by the VR, but this created the risk of destroying your
processor by accidentally running it at very high voltage. Modern proces-
sors use voltage identification (VID) to control the voltage produced by
the VR. When the system is first turned on, the motherboard powers a
small portion of the microprocessor with a fixed voltage. This allows the
processor to read built-in fuses specifying the proper voltage as deter-
mined by the manufacturer. This is signaled to the VR, which then
powers up the rest of the processor at the right voltage.
Microprocessor power can be over 115 W at voltages as low as 1.4 V,
requiring the VR to supply 80 A of current or more. The VR is actually
not a single component but a collection of power transistors, capacitors,
and inductors. The VR constantly monitors the voltage it is providing
to the processor and turns power transistors on and off to keep within
a specified tolerance of the desired voltage. The capacitors and induc-
tors help reduce noise on the voltage supplied by the VR.