• Choose a category
• All
• Classic-Fiction

ATX Form Factor

There continued to be a tremendous demand for a new form factor: a form factor that had more standard connectors and also was flexible enough for possible changes in technology. This demand led to the creation of the ATX form factor in 1995 (Figure 9-7). ATX got off to a slow start, but by around 1998, ATX overtook AT to become the most common form factor used today.

ATX is distinct from AT in the lack of an AT keyboard port, replaced with a rear panel that has all necessary ports built in. Note the mini-DIN (PS/2) keyboard and mouse ports at the left of Figure 9-8, standard features on almost all ATX boards. You recall those from Chapter 2, “The Visible PC,” right?

Figure 9-7 Early ATX motherboard

Figure 9-8 ATX ports

The ATX form factor includes many improvements over AT. The position of the power supply allows better air movement. The CPU and RAM are placed to provide easier access, and the rearrangement of components prevents long expansion cards from colliding with the CPU or Northbridge. Other improvements, such as placing the RAM closer to the Northbridge and CPU than on AT boards, offer users enhanced performance as well. The shorter the wires, the easier to shield them and make them capable of handling double or quadruple the clock speed of the motherboard. Figure 9-9 shows AT and ATX motherboards—note the radical differences in placement of internal connections.

Figure 9-9

ATX motherboards use a feature called soft power. This means they can use software to turn the PC on and off. The physical manifestation of soft power is the power switch. Instead of the thick power cord used in AT systems, an ATX power switch is little more than a pair of small wires leading to the motherboard. We delve into this in more detail in Chapter 10, “Power Supplies.”

The success of ATX has spawned two form factor subtypes for specialty uses. The microATX motherboard (Figure 9-10) floats in at a svelte 9.6 by 9.6 inches or about 30 percent smaller than standard ATX, yet uses the standard ATX connections. A microATX motherboard fits into a standard ATX case or in the much smaller microATX cases. Note that not all microATX motherboards have the same physical size. You’ll sometimes see micro ATX motherboards referred to with the Greek symbol for micro, as in μATX.

Figure 9-10 A microATX motherboard

In 1999, Intel created a variant of the microATX called the FlexATX. FlexATX motherboards have maximum dimensions of just 9 by 7.5 inches, which makes them the smallest motherboards in the ATX standard. Although FlexATX motherboards can use a standard ATX power supply, most FlexATX systems use a special FlexATX-only power supply. This diminutive power supply fits into tight FlexATX cases.

* * *

NOTE Many techs and Web sites use the term mini-ATX to refer to motherboards smaller than a full ATX board. This is technically incorrect. The specifications for these small boards use only the terms microATX and FlexATX.

Keep in mind that each main type of form factor requires its own case. AT motherboards go into AT cases, NLX motherboards go into NLX cases, and ATX motherboards go into ATX cases. You cannot replace one form factor with another without purchasing a new case (Figure 9-11). The exception to this rule is that larger form factor ATX cases can handle any smaller-sized form factor motherboards.

Figure 9-11 That’s not going to fit!

BTX Form Factor

Even though ATX addressed ventilation, faster CPUs and powerful graphics cards create phenomenal amounts of heat, motivating the PC industry to create the “coolest” new form factor used today—the Balanced Technology eXtended (BTX) form factor (Figure 9-12). BTX defines three subtypes: standard BTX, microBTX, and picoBTX, designed to replace ATX, microATX, and FlexATX, respectively.

Figure 9-12 A microBTX motherboard

At first glance, BTX looks like ATX, but notice that the I/O ports and the expansion slots have switched sides. You can’t put a BTX motherboard in an ATX case. BTX does not change the power connection, so there’s