UK What a form factor defines
A form factor is the standard that fixes a component’s size, shape, mounting points and connector positions. A motherboard form factor sets the board’s outline, where the mounting holes sit, where the rear I/O panel goes, how many expansion slots line up with the case and which power connectors it uses. Any board that follows the standard fits any case built to it.
The term is also used one level up. A computer form factor describes the whole system’s shape: tower, small form factor desktop, mini PC, rack mount, panel PC or DIN-rail box. The two are linked, because the board’s size largely decides which chassis shapes are possible.
Form factor is also used for drives and cards, such as 2.5-inch SSDs, M.2 modules and low-profile PCIe cards. This page covers boards and the systems built around them.
Motherboard sizes compared
The table lists the common motherboard sizes, from desktop ATX down to the stackable PC/104 modules used in vehicles and defence equipment. Sizes are the nominal outlines set by each standard.
| Form factor | Board size | Expansion | Typical use |
|---|---|---|---|
| ATX | 305 × 244 mm | Up to 7 slots | Towers, rack chassis, GPU and multi-card systems |
| Micro-ATX | 244 × 244 mm | Up to 4 slots | Smaller towers and rack systems |
| Mini-ITX | 170 × 170 mm | 1 slot | Small industrial PCs, kiosks, appliances |
| 4×4 | 102 × 102 mm | M.2 only | NUC-style mini PCs |
| 3.5-inch SBC | 146 × 102 mm | M.2, Mini PCIe | Fanless box PCs, panel PCs |
| Pico-ITX | 100 × 72 mm | M.2 or pin headers | Space-limited devices and gateways |
| PC/104 | 96 × 90 mm, stacking | Stacked modules | Vehicle, rail and defence systems |
ATX was published by Intel in 1995, and Micro-ATX followed in 1997. VIA introduced Mini-ITX in 2001 and Pico-ITX in 2007. PC/104 is maintained by the PC/104 Consortium, and our guide to the PC/104 form factor covers its stacking buses. Larger boards such as E-ATX exist for dual-processor servers.
ATX, Micro-ATX and Mini-ITX boards
The three desktop sizes share mounting-hole positions, so a smaller board fits a larger case. That is why a Mini-ITX board can go into an ATX tower, but not the other way round. What changes is expansion. Industrial ATX and Micro-ATX motherboards suit systems with several PCIe cards, such as GPUs, frame grabbers or I/O cards. A Mini-ITX motherboard trades slots for footprint and suits most single-card or no-card designs.
Below Mini-ITX, most boards are single board computers with the processor and memory soldered on. Pico-ITX SBCs and 3.5-inch boards are common in fanless systems, where the board bolts to a heatsink or the case wall.
Mini-ITX vs Micro-ATX
Mini-ITX and Micro-ATX are the two sizes most often weighed against each other for a compact build. Micro-ATX is a cut-down ATX board, square and up to 244 mm along each side, while Mini-ITX is smaller again at 170 mm square. Both use ATX mounting points and the same rear I/O cut-out, so either fits an ATX case, and a Mini-ITX board also fits a Micro-ATX case.
| Feature | Mini-ITX | Micro-ATX |
|---|---|---|
| Board size | 170 × 170 mm | Up to 244 × 244 mm |
| Expansion slots | 1, usually PCIe x16 | Up to 4 |
| Memory slots | Usually 2, DIMM or SO-DIMM | Usually 2–4 DIMM |
| M.2 slots | Typically 1–2 | Typically 1–3 |
| Power input | ATX or SFX, or a single DC input on many industrial boards | Standard ATX power supply |
| Typical systems | Compact fanless PCs, panel PCs, appliances | Small towers, 2U–4U rack chassis, multi-card systems |
The choice comes down to expansion. If the system needs one card or none, Mini-ITX gives the smaller chassis and is easier to cool without fans. If it needs a GPU plus a frame grabber, extra network ports or an I/O card, Micro-ATX keeps those slots without the footprint of full ATX. Memory is the other difference: Mini-ITX boards usually carry two memory slots, which can limit capacity on boards that use SO-DIMMs.
You may also see “Micro-ITX” in searches and listings. There is no widely used Micro-ITX standard; the name usually mixes up Mini-ITX and Micro-ATX, so check the board dimensions rather than the label.
Mini-ITX vs Micro-ATX on industrial boards
Industrial boards use the same outlines as desktop boards, but what sits on them shifts the Mini-ITX vs Micro-ATX choice. Performance is rarely the deciding factor: a Mini-ITX and a Micro-ATX board with the same processor and chipset run the same software at much the same speed, as long as the smaller board’s power delivery and cooling can hold the processor at its rated power. The real differences are power input, height, expansion and I/O.
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DC input on Mini-ITX. Many industrial Mini-ITX boards take a single DC input, such as 12 to 28 V or 9 to 36 V, so they run straight from a cabinet or machine supply without an ATX power supply.
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Thin Mini-ITX. A low-profile version of Mini-ITX that keeps the 170 × 170 mm outline but limits component and rear I/O height, so the board fits slim panel PC and all-in-one housings. These boards usually take SO-DIMM memory and a DC input, and many add a header for LVDS display panels or eDP.
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Slots and memory on Micro-ATX. Industrial Micro-ATX boards keep up to four expansion slots, sometimes including legacy PCI beside PCIe, and four DIMM slots for up to 128 GB on current Intel boards. Workstation chipsets such as Intel W680 add support for ECC memory in industrial computers.
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Serial and legacy I/O. The larger board leaves room for more on-board headers, and some Micro-ATX designs carry six serial COM ports for older instruments and controllers.
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Cooling. A fanless Mini-ITX build normally pairs the board with a low-power embedded processor under a heatsink, while a Micro-ATX system with a GPU or several cards usually needs fans or a large chassis with directed airflow.
Computer form factors and the chassis
The chassis is the case that holds the board, power supply, drives and cooling. A computer chassis built for a board form factor provides the standoffs, the rear I/O cut-out and the slot openings. Its own form factor depends on where the system will live.
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Tower. Upright desktop case for ATX or Micro-ATX boards. Room for full-height cards, drives and large coolers.
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Small form factor and mini PC. Desktop or wall-mounted cases for Mini-ITX, 4x4 and SBCs. Many industrial versions are fanless.
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Rack mount. Flat chassis that bolt into a 19-inch rack, with the height given in U: 1U, 2U or 4U, where 1U is one rack unit.
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Panel PC. Computer and touch screen in one housing, mounted in a cabinet door or on a VESA arm.
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DIN rail. Narrow boxes that clip onto the 35 mm rail inside a control cabinet.
Choosing a form factor for an industrial build
In industrial systems the form factor follows the installation, not the other way round. Start with what has to fit and what has to connect.
Count the expansion cards first: a GPU or several I/O cards points to ATX or Micro-ATX, while one card or none leaves the choice open. Then check power input, since many embedded boards take a single DC supply such as 12 V or 9 to 36 V. Cooling comes next, because fanless designs favour boards with a low-power processor mounted under a heatsink. Last, check the mounting space in the cabinet, vehicle or machine. Where space is the main constraint, industrial mini PCs package a small board, storage and I/O in one sealed box. Our guide to choosing an industrial motherboard or embedded SBC walks through the trade-offs.
Quick answers on form factors
Form factors: common questions
What are the main motherboard sizes?
ATX, Micro-ATX and Mini-ITX. Those three cover most desktops and towers. Embedded systems add smaller sizes such as 4×4, 3.5-inch, Pico-ITX and PC/104, and servers use larger boards such as E-ATX.
What does ATX stand for?
Advanced Technology eXtended. Intel published the ATX specification in 1995 to replace the older AT layout. It also defines the standard ATX power supply and its connectors.
What does ITX mean?
Information Technology eXtended. VIA used the name for its family of small boards: Mini-ITX, Nano-ITX and Pico-ITX. Mini-ITX keeps the ATX mounting holes, so it fits ATX and Micro-ATX cases.
Is Micro-ATX bigger than Mini-ITX?
Yes. A Micro-ATX board is up to 244 × 244 mm with up to four expansion slots. Mini-ITX is 170 × 170 mm with one slot, so it suits smaller chassis.
Will a Mini-ITX board fit in an ATX case?
Yes. Mini-ITX uses a subset of the ATX mounting holes and the same rear I/O cut-out, so it fits ATX and Micro-ATX cases. Only the expansion slots go unused.
Does the form factor decide the power supply?
Partly. ATX towers take a standard ATX power supply, and small cases often use the shorter SFX size. Many embedded boards skip both and take a single DC input, fed by an external adapter or the cabinet’s 24 V supply.
What is a barebone PC?
A partly built computer. A barebone PC is a chassis with the motherboard and power supply fitted, but without the processor, memory, storage or operating system. Those parts are added before the system is used.
We build industrial PCs around the board and chassis that suit the installation, and fit the processor, memory, storage and operating system as standard. Tell us the cards, I/O, power input and space you have, and we will specify the form factor to match.