Form Factors: Why is it important when choosing which Single-Board Computer to use?
There are many factors to consider when choosing which Single-Board Computer (SBC) to use. With the vast amount of SBCs to choose from, it can be a dilemma. In this article, we will be focusing on one of the factors: Form Factors.
A common misconception is that form factors only describes the shape and size of the hardware, but it also refers to the physical specification of hardware and the arrangement of the hardware. This is important It can also describe any physical aspect of a computer system. It is commonly referred to as the specification of a motherboard.
In this article we will be going through:
- The Importance of Form Factors
- Standard Sizes of Single-Board Computers, and
- Physical Specification and Arrangement of Hardware.
Importance of Form Factors
An obvious consideration when choosing a form factor is the size. Your project may reserve a big amount of space, to a smaller than palm-sized space for the SBC. If you have a big amount of space, it will be way easier to pick a suitable one. However, if your space is limited, you will be required to pick a smaller SBC. If the SBCis smaller, there will be limited space for many features.
The incompatibility for different components to physically fit into space will arise due to the standardisation of component form factors. For instance, USB-A will not fit into USB-C headers and vice-versa. They are both sized different and will cause damage if forcefully inserted. That’s when you need to consider what functions and I/O you’re looking for and choose accordingly. This is a bigger concern for SBCs.
Single-Board Computer Sizes
There are plenty of different standard sizes for SBC. It can range from 146mm x 203mm to 84mm x 55mm. However, there are only a few common sizes:
| Board Type | Dimensions | Total Area (mm²) |
| Mini-ITX | 170mm x 170mm | 29,667 |
| 3.5 Inches | 102mm x 147mm | 14,839 |
| PC104 | 97mm x 91mm | 8,826 |
| PICO-ITX | 100mm x 72mm | 7,200 |
| Femto-ITX | 84mm x 55mm | 4,620 |
These “standard” sizes for SBCs apply almost all the time only to SBCs designed for industrial use. SBCs for learning and hobbyists rarely follows these “standard” sizes. For example, the popular Raspberry Pi 4 doesn’t follow any standard dimensions. However, it is still good to know about these sizing standards in the case when you ever need to have this knowledge.
Mini-ITX
Ref: Plant Automation Technology
There are multiple ITX standards: Mini, Nano, Pico and Femto. The Mini-ITX is the largest compared to the rest. Originally designed as a low-power product, most Mini-ITX boards now boasts the same amount of power as their bigger peers. It is commonly seen used with socketed-CPUs for modern custom PCs. In SBCs, the size allows its usage in most types of equipment, commonly industrial, in-vehicle and IoT. It can also be found used in many automation technologies, proving its versatility.
3.5 Inches
Ref: Intel
3.5” Intel Saber AL-3500
Unlike the name suggests, 3.5 Inches boards don’t measure 3.5”. The form factor was designed to accommodate the popular 3.5” disk drives, therefore it measures larger than the drive. These boards are ideal choices for SWAP-optimised industrial PCS, Human-Machine Interface Panels and other space-limited applications.
PC104
Ref: PCMag
PC104 Board Stacking
PC104 is a family of standards: PC104, PC104-Plus, PCI-104, PCI-104-Express and PCIe-104. Its name originals from personal-computer (PC) and the 104 pins used to stack the cards together. They are well-known and typically used in a stacked configuration. They are sometimes referred to as “stackable PC”.
Due to the minimal size, weight and rugged built, it is used very widely in military defence electronics. They also provide modularity for future maintainability and upgradeability.
Pico-ITX
PhoenixA20 – First ARM A7 Pico-ITX Board
Part of the ITX family, the Pico-ITX measures 100x72mm. These boards are known to pack lots of typical pc functionality at their small size. It is commonly found used for in-vehicle PCs such as the in-flight entertainment system and also industrial automation systems. They are also found in portable devices.
Femto-ITX
Ref: WinSystems
Femto-ITX is the smallest board size. It will be challenging to find another SBC smaller size than a Femto-ITX. With dimensions slightly smaller than the average palm-size, most hobbyists SBCs are around the same dimensions as a Femto-ITX as well.
Non-industrial Single-Board Computer Size
As mentioned, most SBCs for consumers and hobbyists does not follow these standard sizing. Most manufacturers have their custom sizing for their products. There are some products sizing that is very popular as well. For example, the Raspberry Pi 4 sizing of 85mm x 56mm is very popular among other boards that aren’t Raspberry Pi’s as well. Most non-industrial SBC is also very small (slightly smaller than palm-size), therefore sizing is not as major of a factor when looking at the form factors of different SBCs.
Physical Specification and Arrangement of Hardware
When we are looking at the physical specification and arrangement of hardware, in this case, we are looking at the:
- Availability and Arrangement of I/O ports
- Position of Mounting Holes
When you are looking at these factors, you should consider your needs and match them to these factors.
Availability and Arrangement of I/O ports
Most SBCs provide these common I/O ports: HDMI, USB-A, USB-C, Micro-USB, Ethernet, Audio Jack, and a Micro-SD Card Reader. However, not all of them provide these features. Some of them may also provide more than these. It depends on mostly what the SBC is designed for.
If you are looking to use the Single-Board Computer as a desktop computer to browse the web, watch some entertainments and answer emails, you’ll be looking for an SBC board that allows you to connect your mouse, keyboard, monitor, and speakers. With that, you’ll need an SBC with USB ports, display ports i.e. HDMI, and an audio jack. An example would be this:
ODYSSEY – X86J4105800
Specifications:
- CPU: Intel® Celeron® J4105 1.5 GHz (2.5 GHz boost) w ATSAMD21G18 Cortex® M0+ Coprocessor
- GPU: Intel® UHD Graphics 600
- RAM: LPDDR4 8GBStorage: 64GB eMMC
- Networking: Intel® I211AT PCIe Gigabit LAN, Supports Wake-On-LAN & PXE
With simple connections to Mouse, Keyboard, and Monitor to ODYSSEY – X86J4105, you will get a Desktop Mini PC right away. The ODYSSEY – X86J4105 is more than just a computer, with the Arduino Co-processor onboard, it can be used to connect with sensors, gyroscope, and much more.
If you’re looking for an SBC to work on IoT projects involving many sensors and modules, you’ll want an SBC board that is compatible and easy to connect sensors with. Examples of such projects are the Fish Tank Management system and Plant monitoring system.
There are systems that allow you to connect compatible sensors easily to your board without any soldering. Grove is a modular, standardized connector prototyping system. Compared to solder based systems, all you need to connect a Grove sensor to an SBC is a single cable. The cable will connect to a Grove connector. There are SBCs designed for IoT projects with a built-in grove connector. An example would be:
Seeed Studio BeagleBone Green Wireless Development Board（TI AM335x WiFi+BT)
Specifications:
- CPU: AM3358 1GHz ARM® Cortex-A8
- Coprocessor: 2x PRU 32-bit microcontrollers
- RAM: 512MB DDR3
The BeagleBone® Green Wireless is a product of a collaboration between Seeed Studio and BeagleBone.org. It offers built-in Wi-Fi and Bluetooth with two antennas while supporting AP+STA communication. It also has two Grove connectors to easily connect with the many available Grove sensors and modules. If you’re looking for a board to build a cloud-connected monitoring or communication system, this will be an ideal choice.
Position of Mounting Holes
Mounting holes are holes intentionally built-upon the structure of the SBC board to allow users to mount it to cases or panels. Most boards come with mounting holes that have a standard configuration that allows them to fit onto most compatible enclosures. For example, the aforementioned ODYSSEY – X86J4106, Raspberry Pi, BeagleBone and also the unmentioned Jetson Nano all comes in similar sizes with identical mounting holes that allow many different enclosures to be compatible with them. Here’s an example:
Re-computer Case
The re_computer case is specifically designed to be used for the re_computer system, but it is compatible with all popular Single-Board Computers: ODYSSEY – X86J4106, Raspberry Pi, BeagleBone and also the unmentioned Jetson Nano. It comes with a removable acrylic cover on the top, and also a stackable structure to extend its usage. It is well-reviewed and received good endorsements from various companies. Techradar mentioned: “We recommend getting the official Odyssey enclosure … as it is well worth its price tag.”.
There are several SBCs that does not come with standard mounting holes that make it difficult to find compatible enclosures or panels. Therefore, looking for an SBC with standard mounting holes will ensure maximum compatibility.
Summary
To conclude when looking at the form factor of the SBC, it is important to consider the requirements of I/O ports for your project. Mounting holes will also be a good thing to consider to see whether or not you would want to use specific cases or panels to mount your SBC on. Most SBC are smaller than palm-sized so it will only be important to consider the size of your SBC if your project has a lot of space limitation for the SBC.
Here is some more recommended reading to help you with choosing an SBC for your project:
- Best Single Board Computers of 2021
- Raspberry Pi Alternatives: 17 Best Single Board Computers in 2021
- All about CPUs: Microprocessor, Microcontroller and Single Board Computer
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