Chapter 4: Motherboards^79
TheATXdesign(seeFigure4-4)alsoincorporatesanumberoffeaturesintothepower
supply. The power on and off functions can be controlled by the motherboard, a feature
calledsoft switching. Power supply connectors are a one-piece keyed fit that cannot be
connected incorrectly, preventing the possibility of a fried motherboard and personal
injuries. The ATX power supply also suppliessplit voltage, which is a range of voltages,
usually12v,5v,and3.3v,tothemotherboard,eliminatingtheneedforavoltageregulator
on the motherboard.Mini-ATX
A subspecification of the ATX spec is the mini-ATX. Despite its name, this form factor is
only slightly smaller than the ATX form. Other subspecifications of the ATX form factor
you may encounter are the Micro-ATX and the Flex-ATX.NLX Form Factor
A new standardized form factor is the NLX low-profile motherboard, shown in Figure 4-5.
This board design supports many current and emerging technologies as well as support
for AGP (Accelerated Graphics Port) video adapters and tall memory modules. The
design goals of the NLX form are easy removal and replacement of the motherboard
without tools and to provide more flexibility for system-level functions. The NLX uses
the backplane design approach that includes a riser board for expansion cards.Figure 4-4. An ATX motherboard. Photo courtesy of AOpen America, Inc.