|Name||PCB size (mm)|
|WTX||356 × 425|
|AT||350 × 305|
|Baby-AT||330 × 216|
|BTX||325 × 266|
|ATX||305 × 244|
|EATX (Extended)||305 × 330|
|LPX||330 × 229|
|microBTX||264 × 267|
|NLX||254 × 228|
|Ultra ATX||244 × ?|
|microATX||244 × 244|
|DTX||244 × 203|
|FlexATX||229 × 191|
|Mini-DTX||203 × 170|
|EBX||203 × 146|
|microATX (min.)||171 × 171|
|Mini-ITX||170 × 170|
|EPIC (Express)||165 × 115|
|ESM||149 × 71|
|Nano-ITX||120 × 120|
|COM Express||125 × 95|
|ESMexpress||125 × 95|
|ETX/XTX||114 × 95|
|Pico-ITX||100 × 72|
|PC/104 (-Plus)||96 × 90|
|mobile-ITX||60 × 60|
Mini-ITX is a 17 x 17 cm (or 6.7 x 6.7 inches) low-power motherboard form factor developed by VIA Technologies. Mini-ITX is slightly smaller than microATX. Mini-ITX boards can often be passively cooled due to their low power consumption architecture, which makes them useful for home theater 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 this is 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 arround non-x86 processors have a 3.3V PCI slot, and some newer boards have a PCI-express x16 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 mm x 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 mm x 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 are still primarily industrial boards, with the majority sold in bulk for less exciting applications. They are produced with a much longer sales lifetime than consumer boards (the original EPIAs are still available), something that industrial users need. 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 and advertising display boards.
To date there have been three generations of VIA's Mini-ITX boards: the original PL133 chipset boards (affectionately known as "Classic" boards), CLE266 chipset boards (adding MPEG-2 acceleration), and CN400 boards (which added MPEG-4 acceleration). Second generation boards include the EPIA M, MII, CL, PD, TC and MS — all tailored to slightly different markets. The EPIA SP is the first and only CN400 board to be released to date. All current VIA boards use their x86-compatible CPU — the C3, or its lower power Eden variant. In 2006 the next-generation C7 CPU was released in a new line of VIA boards. Other manufacturers have also produced boards using 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 is a huge leap forward compared to previous VIA C3 and C7 offerings and a 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.
Since VIA focuses on IPC, their Mini-ITX products were designed and sold to the industrial and System Integrator markets. AOpen Inc. is the primary early provider that designed and marketed Mini-ITX motherboards to the consumer market in 2006.
The first AOpen Mini-ITX motherboard is i945GTt-VFA, it supports 667 MHz FSB Intel Core Duo/Core Solo Socket 479 CPU and Intel Viiv technology for setting up a HTPC (Home Theater PC). The latest AOpen Mini-ITX motherboard is nMCP7ASt-V that adapts Socket 775 Intel Core 2 Quad/Core 2 Duo/Celeron FSB 533/800/1066/1333 MHz CPU, Dual Channel DDR2 667/800 MHz SDRAM up to 4GB, and a PCI Express x 16 Slot (Support nVIDIA Hybrid SLI technology and PCI Express 2.0 via nVIDIA MCP7A-S chipset).
Recently (as of Nov. 2009), DFI announced a mini-ITX P55 based motherboard. The board features the LGA-1156 socket with support for Core i5/i7 CPUs. It has a 6-phase PWM, and ABS II CPU auto upgrade technology if you wish to overclock. It includes two DDR3 memory slots, and a single PCI-Express x16 slot which is required due to the lack of integrated graphics. For connections it has eSATA and 3xSATA II ports, 4XUSB 2.0, Gigabit LAN ,8 channel audio with SPDIF, along with CMOS reset button and debug LED. 
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 to 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 used a 20 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 adaptor and the DC-DC board are supplied with the case.
Some boards have built in DC-DC converters and converters have also been made that plug directly onto the ATX connector (e.g. the picopsu), either of these options avoids the need to mount a separate DC-DC converter in the case saving space and design effort. Boards using full-power Intel or AMD CPU's typically use ATX12V 2.x connections and require a case with appropriate power supply and cooling for these more power hungry chips.