Small, all-in-one computer board designed for compact use or in embedded devices.
"…small computers that contain on one board their processor, RAM, and either onboard storage (in the form of eMMC flash memory), or a storage connector like a microSD or M.2 slot that allows flash storage to be directly mounted)."
—Christopher Barnatt
Think of an SBC as a computer motherboard fully populated with processor, memory, with storage and peripheral connectivity available. Many of the early home and hobbyist computers had this design philosophy, for example the KIM-1, the BBC Micro and Acorn Electron. As time went on, and especially after IBM began the PC line (followed by myriad clone manufacturers, computers began to be built with more and more plug-in peripherals such as dedicated video, sound and network cards, RAID controllers, modems and the like.
With wider acceptance of increasingly powerful desktop computers, the concept of al all-in-one computing solution slipped into the background. With the increasing adoption of USB for peripheral connectivity, the stage was set for a return to more compact single-board solutions. In 2012, the Raspberry Pi SBC was released in the UK, using a Broadcom SOC (system-on-a-chip) and featuring a GPIO (general-purpose input/output) interface for connecting external components like sensors, switches and hardware controllers.
The SOC, integrating CPU, memory and I/O controllers, was at the heart of these boards, and very quickly they became useful for teaching students about both hardware and software concepts, in the same way the BBC Micro had years earlier. Soon they were ubiquitous in schools and universities and it wasn't long before computer hobbyists began to see the potential for building things such as robots, home automation and dedicated portable genera-purpose computing devices. The "maker" community quickly picked up on the versatility of Raspberry Pi, and as the number and power of these devices expanded, other manufacturers began to jump on the bandwagon, and soon there was a bewildering variety of SBCs available, most with the tiny footprint of the original Pi. Most of these boards are based on ARM architecture SOCs, rely on FOSS (free, open-source software, mostly based on Linux) so here is a wide and ever-expanding playing field of software that allows for almost anything to be built at low cost, with the other outlay of a while reading and tinkering.
As makers, IT and tech "influencers" began to make both the boards and their projects public, there was an explosion of interest thanks to widespread availability of ideas (through hobbyist forums, YouTube, Reddit and the like). Every maker faire had a plethora of devices showing off the versatility of these boards and the rush began, both from the public to procure them, and competitors to clone the idea. The new marketplace of SBCs has brought experimentation to a new generation of students, home users, geeks and nrds around the world. There are people running homelabs, cyberdecks and all manner of quirky things. A quick lance on YouTube will show hundreds of people using SBCs to drive all sorts of funky and clever projects. One of my favourites is the guy who built a portable NAS/router to take on vacation with his family. Using FOSS software projects, if you can imagine it, you can make it with an SBC, even to th point of building a cluster of them to create a mini "supercomputer", which yes, has been done (using kubernetes.¹
¹Pi supercomputer cluster
$ xclip -o | wc -w
561