PC Hardware A Beginner’s Guide

(^78) PC Hardware: A Beginner’s Guide
port,andablankslotthatcouldbeusedforasecondparallelport.Thebottomrowincludes
a second PS/2-type keyboard or mouse connector, two serial ports, and a series of blank
ports that might be used for sound or video card connectors. The defined size of the
connector area on an ATX motherboard is small (6.25 inches by 1.75 inches), which helps
eliminate the clutter of cables found near the rear panel of a Baby AT motherboard.
The ATX form factor is a result of the lessons learned from Baby AT and LPX mother-
boards. The ATX locates the CPU and RAM mountings away from the expansion cards
and close to the power supply fan, as shown in Figure 4-3. This arrangement improves
the airflow available to cool the CPU and RAM chips. Originally, the ATX specification
had the power supply’s fan pulling air into the case, over the CPU, and out the vents on
the case, in an effort to eliminate the need for a separate CPU fan. This design resulted in
dust and other airborne particles (like chalk dust, metal filings, and more) being pulled
into the case and settling inside. Instead of eliminating fans, the result was that the case
actually required additional fans to cool the CPU properly, not to mention clogged up
and shorted out PCs. Newer ATX versions now have the fan venting the case. The ATX
design also allows for additional case fans, which are recommended for PCs with 3D
video accelerators, other high-heat producing cards, or multiple hard disk drives.
Figure 4-3. The standard ATX motherboard layout