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If you’re a system developer or systems integrator, you likely have a dilemma: which single board computer form factors do I deploy in my system? We’ll go through some of the more popular form factors primarily by size so you can make an informed decision. The form factors covered in this article generally feature the small size, rugged design, extended operational temperature, and long lifecycle so important to demanding applications in harsh environments. Standard form factors also provide the convenience of COTS availability and reduce integration time. We’ll cover them by size, from largest to smallest.

Form Factor	Dimensions (mm)	Expansion Style	Primary Use Case
EBX	146 x 203	On-board I/O & PC/104 Stacking	High-Performance Automation: Large footprint for high-wattage CPUs and extensive built-in connectivity.
EPIC	115 x 165	PC/104-Plus Stacking	Rugged Industrial Computing: The “middle ground” for systems requiring a mix of legacy and modern I/O in a mid-sized footprint.
3.5-inch	146 x 102	Cable-based / Daughterboard	Embedded Control Systems: The industry standard for fanless, low-profile enclosures where vertical height is restricted.
PC/104	90 x 96	Self-Stacking (No Cables)	Aerospace & Defense: High-vibration environments where a “brick” of stacked modules replaces failure-prone cables.
Pico-ITX	100 x 72	High-Density Connectors	Mobile & Medical Devices: Ultra-compact handhelds or IIoT gateways where minimal weight and size are the top priority.

Since the embedded computing industry’s inception, the trend has been toward achieving smaller size and weight with higher performance under lower power use. As you consider the size, weight and power (SWaP) requirements of your design which needs an embedded computer, which factor do you prioritize? For example, many newer applications require higher performance, which often results in more power being consumed and more heat generated. The smaller footprint SBCs provide less area to dissipate that heat, which may result in taller package once an adequate thermal solution is added.

 

EBX: Big, But Not Too Big

The Embedded Board, eXpandable, or EBX standard, is the physically largest of those covered here. It’s governed by the and the specification is freely available. The EBX SBC is large enough to hold all the functions of a full embedded computer system, including a CPU, memory, mass storage interfaces, display controller, serial/parallel ports, and other functions.  The EBX is popular where there is more space for the x-y axis and less in the z-axis, providing options for less dense connectors, which can help cabling costs and with heat dissipation over the larger board area.��

An EBX SBC can be expanded with standard modules, including any of the stackable PC104 variants. This makes the board highly customizable, as there are many PC104 modules available. The combination of EBX plus PC104-Plus results in processor independence for the developer. An example of such a board is the �±������۳��շ��ѳ�’ EBC-C413, an industrial SBC built with the Intel Atom® E3800 series CPU, dual Ethernet, serial ports and 48 general purpose I/O (GPIO).

 

Mini-ITX

There are multiple ITX standards; from largest to smallest, they are the Mini, Nano, Pico, and Femto. The Mini-ITX is quite large compared to the rest of the boards covered here, measuring slightly smaller than the EBX SBC. The size permits use in most types of equipment, including in-vehicle, industrial, and IoT. While originally designed as a low-power product, Mini-ITX boards now encompass just about any flavor and are often targeted at commercial designs without rugged or industrial specifications requirements.

 

EPIC

Next is the EPIC form factor, whose boards tend to feature multiple I/O, unified connectors along the edge of the PCB, the ability to stack PC104-Plus expansion modules and operate in extended temperatures. These boards often find homes in higher performance applications and have a relatively easy path to future upgrades. The EPIC-compatible EPX-C414 from 91���� uses the Intel Atom Bay Trail E3845 or E3825 processor. Its rugged design and extended operational temperature suit it for industrial applications.

 

 

 

3.5 Inch (3.5″)

You would think that the 3.5″ form-factor board would measure 3.5 inches. However, you’d be wrong. The form factor was developed to accommodate the hosting of the popular 3.5″ disk drives. Hence it measures larger than the drive (which actually measures 3.6 by 3.5 in.), coming in at 5.75 by 4 inches. This gives some space beyond the drive to house other electronics, assuming you embedded a rotating disk drive. Such SBCs are often lower profile and fanless, which means that they typically operate at lower power levels.  The 3.5″ form factor serves well in a wide range of embedded and industrial IoT use cases.

�±������۳��շ��ѳ�’ SBC35-427 industrial single board computer can be configured with either a dual-core or quad-core Intel Atom Apollo Lake-I E3900 series processor. It is designed for demanding applications that balance power use. 91���� also offers the rugged SBC35-474 3.5″ SBC powered by an Intel Atom Amston Lake x7000RE Series processor with integrated 16UE GPU to provide robust performance for latency-sensitive applications.�� Both models combine off-the-shelf COTS functionality with multiple expansion and configuration options and operate from -40° to +85°C without active cooling.��

 

PC104

encompasses a slew of standards derived over time, from the original PC104 to PC104-Plus, PCI-104, PCI104 Express, and PCIe104. The form factor gets its name from its personal-computer (PC) origins and the 104 pins that are used to connect the cards together. All variations share the same dimensions. These cards are typically used in a stacked configuration consisting of the main SBC plus expansion boards to meet specific application requirements.

PC104-Plus added support for the PCI bus to the original standard, which uses the ISA bus. The PCI-104 form factor keeps the PCI connector, but removes the PC104 connector, in an effort to maintain high performance while increasing the available board real estate. In this variant, the connector contains 120 pins, but the “104” naming convention remained intact. The PCI connector location and pinout are identical to PC104-Plus.

An example of a PC104-Plus offering is the �±������۳��շ��ѳ�’ PPM-C412 SBC. It features a DMP Vortex86DX3 SoC processor, a rugged design, and an extended temperature range, putting it into industrial IoT applications and embedded systems like industrial controls, transportation, Mil/COTS, and energy.

Both the PCI104-Express and PCIe104 specification added an option for the PCIe/104™ OneBank™ expansion, which takes advantage of a smaller, lower-cost bus connector, yet is compatible with the full-size PCIe104 connector. This option lets designers stack boards using a complementary format that frees up board real estate for additional components or a cost reduction. �±������۳��շ��ѳ�’ PX1-C441-3950 is an example of such an SBC.

 

PICO-ITX

The Pico-ITX shares many of the same characteristics as the Mini-ITX form factor, yet it measures significantly smaller at 100 by 72 mm. Board vendors have done a great job at maximizing that small space, packing in a lot of functionality. The small size suits the SBCs for in-vehicle PCs, in-flight entertainment systems, industrial automation systems, and portable devices.

As components get more integrated and shrink in size, it allows for more dense packaging, as evidenced by the availability of Pico-ITX products such as the WINSYSEMS ITX-P-C444.��

 

 

Finally, the Femto-ITX boards take you to a tiny 84 by 55 mm. You’d be hard pressed to find a standard form factor smaller than Femto-ITX. Suitable applications include UAVs, medical, robotics, and digital signage.

Next Steps

Now that you’ve seen some strong choices for rugged single board computer form factors, to see what 91���� offers in your preferred size, processor choice and I/O, use the product filter on our SBC products page to find suitable SBCs. However, if you really need something that doesn’t fit one of these form factors, a custom form factor is always a possibility. 91���� has extensive expertise in the design and manufacturing of rugged embedded SBCs and systems, so contact us to discuss custom configurations to best meet your requirements.