Mini-ITX is a 17×17 cm (or 6.7×6.7 inches) low-power motherboard form factor developed by VIA Technologies in 2001. They are commonly used in small form factor (SFF) computer systems. Mini-ITX boards can often be passively cooled due to their low power consumption architecture, which makes them useful for home theater PC systems, where fan noise can detract from the cinema experience. The four mounting holes in a Mini-ITX board line up with four of the holes in ATX-specification motherboards, and the locations of the backplate and expansion slot are the same (though one of the holes used was optional in earlier versions of the ATX spec). Mini-ITX boards can therefore often be used in cases designed for ATX, micro-ATX and other ATX variants if desired.
The form factor has provision for one expansion slot, conventionally a standard 33 MHz 5V 32-bit PCI slot. Many case designs use riser cards and some even have two-slot riser cards, although the two-slot riser cards are not compatible with all boards. Some boards based around non-x86 processors have a 3.3V PCI slot, and the Mini-ITX 2.0 (2008) boards have a PCI-express ×16 slot; these boards are not compatible with the standard PCI riser cards supplied with cases.
In March 2001, the chipset manufacturer VIA Technologies released a reference design for an ITX motherboard, to promote the low power C3 processor they had bought from Centaur Technology, in combination with their chipsets. Designed by Robert Kuo, VIA's chief R&D expert, the 215×191 mm VT6009 ITX Reference Board was demonstrated in "Information PC" and set-top box form factors. He would later go on to design the Mini-ITX form factor. The ITX form factor was never taken up by manufacturers, who instead produced smaller boards based on the very similar 229×191 mm FlexATX form factor.
In October 2001, VIA announced their decision to create a new motherboard division, to provide standardized infrastructure for lower-cost PC form factors and focus on embedded devices. The result was the November 2001 release of the VT6010 Mini-ITX reference design, once again touted as an "Information PC", or low cost entry level x86 computing platform. Manufacturers were still reticent, but customer response was much more receptive, so VIA decided to manufacture and sell the boards themselves. In April 2002 the first Mini-ITX motherboards—VIA's EPIA 5000 (fanless 533 MHz Eden processor) and EPIA 800 (800 MHz C3)—were sold to industrial customers.
Enthusiasts soon noticed the advantages of small size, low noise and power consumption, and started to push the boundaries of case modding into something else—building computers into nearly every object imaginable, and sometimes even creating new cases altogether. Hollowed out vintage computers, humidors, toys, electronics, musical instruments, and even a 1960s-era toaster have become homes to relatively quiet, or even silent Mini-ITX systems, capable of many of the tasks of a modern desktop PC.
Mini-ITX boards primarily appeal to the industrial and embedded PC markets, with the majority sold as bulk components or integrated into a finished system for single-purpose computing applications. They are produced with a much longer sales life-cycle than consumer boards (some of the original EPIAs are still available), a quality that industrial users typically require. Manufacturers can prototype using standard cases and power supplies, then build their own enclosures if volumes get high enough. Typical applications include playing music in supermarkets, powering self-service kiosks, and driving content on digital displays.
VIA has continued to expand its Mini-ITX motherboard line. Some of the earlier generations included the original PL133 chipset boards (dubbed the "Classic" boards), CLE266 chipset boards (adding MPEG-2 acceleration), and CN400 boards (which added MPEG-4 acceleration). Second generation boards featured the EPIA M, MII, CL, PD, TC and MS — all tailored to slightly different markets. Legacy VIA boards use their x86-compatible CPUs — the C3, C7 or low-power Eden variants, with newer boards featuring the VIA Nano CPU, launched in May 2008. Other manufacturers have also produced boards designed around the same form factor, using VIA, but also Intel, AMD, Transmeta and PowerPC technology.
Intel has introduced a line of Mini-ITX boards for the Atom CPU, which demonstrates a significant increase in processing performance (but without added power consumption) over older VIA C3 and C7 offerings and is key to making the form factor viable for use in personal computers. Other manufacturers saw the potential of the form factor and followed suit, some even not limiting themselves to the Atom, as evidenced by Zotac GeForce 9300-ITX board that supports Core 2 Duo CPUs with FSB frequencies up to 1333 MHz, two separate-channeled 800 MHz memory slots and fully functional PCI Express 2.0 x16 slot that could connect through SLI to the onboard video. This new wave of offerings has caused Mini-ITX to explode in popularity among home users, hobbyists and even overclockers.
Consumer product 
Since VIA focuses on IPC, their Mini-ITX products were designed and sold to the industrial and system integrator markets. Aopen is the primary early provider that designed and marketed Mini-ITX motherboards to the consumer market in 2006.
Intel-based products 
Intel Pentium (775) processors were supported in the early mITX formats. Intel Atom processors are currently used solely on mITX format motherboards.
There are many contemporary LGA1155 mainboards for Sandy Bridge and Ivy Bridge CPUs in Mini-ITX form-factor on the market now. A typical Mini-ITX LGA1155 mainboard not only allows for integrated graphics, but can also take an external graphics accelerator. That is why there is often a PCI Express 2.0 x16 slot. Moreover, many mainboard makers provide their products with additional mini-PCI Express slots that can be used for extra expansion cards, such as Wi-Fi, TV-tuner cards, SSD, etc. SATA 6 Gbit/s and USB 3.0 are often supported on the original versions of these mainboards, which is why Mini-ITX LGA1155 mainboards can be high-performance / up-to-date platforms.
AMD-based product 
AOpen also made the first AMD based Mini-ITX motherboard, the MCP68PVNt-HD, it supports HDMI and HDCP for home theater PC systems and comes with the MCP68PVNT chipset for AMD Athlon 64 X2, Athlon 64, and Sempron CPU with AM2 socket. The MCP68PVNT supports DirectX 9 and the H.264 hardware decoding decreases the CPU load when playing HD content. AOpen nMCP68PVNt-HD has a HDMI port that support 480P, 720P and 1080P high-definition video and audio with HDCP.
The Mini-ITX standard does not define a standard for the power supply, though it makes some suggestions of possible options. Conventionally Mini-ITX boards use a 20- or 24-pin "original ATX" power connector. This is usually connected to a DC-DC converter board which in turn is connected to an external power adapter. Generally both the power adapter and the DC-DC board are supplied with the case.
Some boards have built in DC-DC converters and converters have also been made to plug directly into the ATX connector (e.g. the PicoPSU), either of these options avoids the need to mount a separate DC-DC converter into the case, saving space and design effort. Boards using full-power Intel or AMD CPUs typically use ATX12V 2.x connections and require a case with appropriate power supply and cooling for these more power-hungry chips.
See also 
|Wikimedia Commons has media related to: Mini-ITX|
- EPIA, Mini-ITX, Nano-ITX and Pico-ITX motherboards from VIA
- Home Theater PC
- Mini ATX, 15×15 cm form factor developed by AOpen
- Mini ITX (whitepaper), TW: VIA.
- Mini-ITX Interface Specification, version 1.1/1.2, Intel
- "Mini-ITX 2.0 Standard" (announcement). TW: VIA.
- VIA Nano Processor Family launch (press release), TW: VIA, May 2008.
- Stores, Tom’s hardware.
- Review, Tech Report.
- D425KT_TechProdSpec.pdf D425KT (PDF) (reference manual), Intel, p. 51.
- Eight Mini-ITX Mainboards for LGA1155 Processors (roundup), xBit labs.
- Product (spec), AOpen.