This document provides an overview of the ITX and Mini ITX motherboards for personal computers.
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Saturday, October 19, 2013 6:14 PM
The ITX / Mini ITX Motherboard
FlexATX defines a board that is up to 9 inches×7.5 inches. A FlexATX board can be smaller than that, but how much smaller? By analyzing the FlexATX specification—and, in particular, studying the required mounting screw locations—you can see that a FlexATX board could be made small enough to use only four mounting holes (C, F, H, and J). Refer to Figure 4.16 for the respective hole locations.
VIA Technologies Platform Solutions Division wanted to create a motherboard as small as possible, yet not define a completely new and incompatible form factor. To accomplish this, in March 2001 VIA created a board that was slightly narrower in width (8.5 inches instead of 9 inches) but still the same depth as FlexATX, resulting in a board that was 6% smaller and yet still conformed to the FlexATX specification. VIA called this ITX but then realized that the size savings were simply too small to justify developing it further, so it was discontinued before any products were released.
In April 2002, VIA created an even smaller board that featured the absolute minimum width and depth dimensions allowed by FlexATX. The company called it Mini-ITX. In essence, all Mini-ITX boards are simply FlexATX boards that are limited to the minimum allowable dimensions. All other aspects, including the I/O aperture size and location, screw hole locations, and power supply connections, are pure FlexATX. A Mini-ITX board fits in any chassis that accepts a FlexATX board; however, larger boards will not fit into a Mini-ITX chassis.
According to the FlexATX standard, the distance between holes H and J is 6.2 inches, and the distance between hole J and the right edge of the board is 0.25 inches. By leaving the same margin from hole H to the left edge, you could make a board with a minimum width of 6.7 inches (0.25 inches + 6.2 inches + 0.25 inches) that would conform to the FlexATX specification. Similarly, the distance between holes C and H is 6.1 inches, and the distance between hole C and the back edge of the board is 0.4 inches. By leaving a minimum 0.2-inch margin from hole H to the front edge, you could make a board with a minimum depth of 6.7 inches (0.4 inches + 6.1 inches + 0.2 inches) that would conform to the FlexATX specification. By combining the minimum width and depth, you can see that the minimum board size that would conform to the FlexATX specification is 6.7 inches×6.7 inches (170mm×170mm).
The Mini-ITX form factor was designed by VIA especially to support VIA’s low-power embedded Eden ESP and C3 E-Series processors. However, third-party vendors have also adopted this form factor for use with low-power netbook-class chips such as Intel’s Atom and AMD’s E- and C-series, as well as with more powerful processors such as Intel’s Core i3 or Core i5, and AMD’s Phenom, Athlon 64 X2, Athlon 64, Athlon II, Phenom II, or Sempron 100. Mini-ITX systems that use these processors can be used as multimedia servers and small form factor PCs as well as for set-top boxes and computing appliances.
The size of the DTX and ITX families of motherboards as they relate to FlexATX is shown in Table 4.5.
Whereas the still-born ITX format was virtually the same as FlexATX in size (which is probably why it was discontinued before any were sold), the Mini, Nano, and Pico-ITX form factors are considerably smaller than FlexATX, as is the mini-DTX.
To take advantage of the smaller Mini-ITX format, several chassis makers have produced small chassis to fit these boards. Most are the shape of a small cube, with one floppy and one optical drive bay visible from the front. The layout of a typical Mini-ITX motherboard, the ASRock M67M-ITX, is shown in Figure 4.19. Nano-ITX and Pico-ITX can fit into slimline (half-U) cases that can be used horizontally or vertically.
Mini-ITX motherboards can offer a full range of input-output ports. And, while designs that use VIA processors typically feature soldered-in place processors and lack PCIe expansion slots, designs that use Intel or AMD processors support a wide range of processors and feature a PCIe slot. However, Mini-ITX and smaller motherboards in the family are not suitable when you need a highly expandable system (most feature only one expansion slot) or when you plan to use processors with more than 100W thermal design power (TDP).
The smaller Nano-ITX and Pico-ITX motherboards use soldered-in-place low-power netbook/embedded-class processors from VIA, Intel or AMD.
Motherboards that are not one of the industry standard form factors, such as any of the ATX, DTX, or ITX formats, are deemed proprietary or semiproprietary. Most people purchasing PCs should avoid proprietary designs because they do not allow for a future motherboard, power supply, or case upgrade, which limits future use and serviceability of the system. Proprietary systems are disposable PCs because you can neither upgrade them nor easily repair them. The problem is that the proprietary parts often come only from the original system manufacturer, and they usually cost much more than industry standard parts. Therefore, after your proprietary system goes out of warranty, it is essentially no longer worth upgrading or repairing. If the motherboard or any component on it goes bad, you will be better off purchasing a completely new standard system than paying many times the normal price for a new proprietary motherboard. In addition, a new industry standard motherboard would be newer and faster than the one you would be replacing. In a proprietary system, the replacement board would not only cost way too much, but it would be the same as the one that failed.