04/10/2019 - Differences between Main Form Factors of Single-Board Computers

Single-board computers (SBCs) are—as the name might imply—computers built on one continuous circuit board. Typically containing microprocessors, memory, and input/output functions, an SBC can be as simple as the Raspberry Pi plugged into your Android phone or as complex as the laptop you use at work. Often, SBCs eschew expansion slots for peripheries in favor of static RAM and low-cost processors. SBCs can be used in routers and network bridges, MP3 players, video game consoles and printers. It’s likely that even your washing machine and A/C have SBCs in them, in the form of “embedded systems.”

Like any piece of IT hardware, SBCs come in a wide variety of form factors—and it’s important to know which type of SBC you might need for a project at home or at work. The most common types of SBCs you’ll encounter at home are Mini-ITX, but commercial options include CompactPCI, AdvancedTCA, and PC/104, all of which are regulated by the PCI Industrial Computer Manufacturers Group, or PICMG.

Now that you know what your options are, let’s run down the list and talk about each form factor’s specs and uses!

1. Mini-ITX

A 6.7”x6.7” motherboard developed by VIA Technologies back in 2001, the Mini-ITX is a staple mobo for any small-sized computer system. Originally designed for low power consumption rigs like home theater PC systems, they would later become popular in industrial and embedded PC markets, typically integrated into systems for single-purpose computing applications. Two important factors set it apart from its competitors: First, these boards have mounting holes, back plates and expansion slots in the same spot that their larger, beefier ATX/Micro-ATX cousins do—so they can almost always be slotted into computer cases designed for larger mobos. Second, they boast a much longer life cycle than those of other consumer boards, which is extremely handy for industrial applications. Some of the original EPIAs are still available for purchase!

These boards can often be found playing music overhead in grocery stores, providing power for self-service kiosks at airports and supermarkets, and powering digital displays. Their ubiquity is helped by the fact that VIA still expands the line to this day, adding multiple chipsets in their first generation, and expanding to a second and third generation in the years since! Intel even introduced their own line for their ultra-low-voltage IA-32 Atomic processors.

Like most SBCs, these little fellas are best put to work in industrial applications—but you’re likely to have on in your monitor, phone and television, quietly humming away to power the many devices you use in your day-to-day life.


2. CompactPCI

A little more focused in its design purpose, the CompactPCI—often referred to as a cPCI, though this isn’t an industry standard abbreviation—is a standard bus interconnect for industrial rigs. Standardized in 3U or 6U sizes, cPCIs are usually interconnected through a passive backplane, the pin assignments of which are standardized by the PICMG

The original run of cPCIs were created in late 1995, but have since been upgraded to the 2.x series, which includes upgrades like support for hot swapping, telephony signaling, and an architecture expansion for switched Ethernet. Though they were initially designed to support PCI signaling protocol, cPCIs have expanded to focus on the application of 2mm HM connectors on other 3U and 6U form factor devices.

cPCI’s greatest technological drawback is, surprisingly, physical in nature! Despite being extremely handy for a wide variety of bus interconnection, roughness won’t be tolerated. Manhandling a cPCI connector can easily bend its signal pins, turning your SBC into a lemon!

3. AdvancedATCA

Though the first entry on this list is the most recognizable form factor in personal application, the Advanced Telecommunications Computing Architecture—AdvancedTCA or ATCA—is easily the most significant in terms of commercial applications. Created in December of 2002, ATCA is a massive specification effort kicked off by the PICMG that includes more than 100 participatory companies.

ATCA was initially designed to produce communications equipment that was “carrier grade”—hardware or software that is well-tested and proven to be reliable—but has more recently grown to encompass military and aerospace technology, focusing on creating rugged tech that can stand up to the rigorous demands of both sectors.

These boards are some of the most durable in the industry, so you’re not likely to be slapping one on the computer in your study anytime soon. They’re designed with metal front panels and bottom covers to limit electromagnetic interference and curb the risk of fire spread in the event of an emergency and have locking injector-ejector levers that trigger hot swap procedures manually. If that sounds a little outside your purview as a hobbyist, that’s fine—ATCA boards are extremely specialized, and if you don’t work in an industry where they’re regularly used, you may never even interact with one

4. PC/104

Back to embedded systems! The PC104 form factor is, first and foremost, a family descriptor. They comprise a series of small motherboards that are most frequently used in environments where small, durable computer systems are a necessity—typically extreme environments where equipment failure could mean catastrophe for everyone involved, up to and including in outer space!

A huge appeal in the PC104 architecture is its stackability. The location of connectors on these modules allow them to be connected top to bottom like building blocks, such that a single PC104 stack could include a CPU, PSU and peripheral modules for networking or data collection, each joined by stand-offs. Despite their size, however, the PC104 boasts surprisingly high processing capabilities, often able to operate multiple special-purpose peripherals simultaneously, like GPS, networking switches, video relay and data collection devices.

And, as mentioned, the PC104 is inherently rugged. They’re compact and possess excellently placed corner mounting holes, guaranteeing very little printed circuit board flex in high-vibration situations. Furthermore, most PC104 modules are designed with extreme temperature components, allowing operation outside of standard temperature fluctuations.

Unless you plan to get some work done on the surface of Mars, inside a volcano, or aboard the International Space Station, it’s not entirely likely that you’ll have need of a PC104 SBC… but they’re handy little boards, and worth knowing about, nonetheless.

There you have it—the four most common types of single-board computers. It wouldn’t be surprising if you had only heard of the first entry on our list before perusing it, so we hope you’ve learned something valuable about SBCs today!

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