Single board computers are computers mounted on a single board. In this case, the board is a circuit board, and the computer is a range of components - microprocessors, memory, and input/output.
A single board computer is differentiated from a desktop or personal computer not by what it can do, but by its design. A single board computer has all elements of a complete computer contained within one circuit board. Conversely, desktop computers have motherboards with slots for the essential components of the computer. On a desktop computer, the processor, memory, storage, input and output devices, and other basic components attach via sockets on the motherboard. On a single board design, everything is self-contained.
Single board computers also have different capabilities than desktop computers. On a desktop computer, adding capability to the motherboard is typically accomplished by plugging a peripheral device into a slot on the motherboard. A high-end video card, for instance, will be plugged into a specialised slot on the motherboard. On a single board computer, this and the other components required are simply part of the circuit board. The device is ready to be used as it is.
Single board computers come in a huge range of different capacities. Because some of them are used to control straightforward processes, some single board computers are very slow and limited compared to the average desktop computer.
Over the past 10 years, there has been a healthy growth of single board computers. They’re small, inexpensive, and cheap to run, but that doesn’t mean they are slouches in performance. A machine in the £50–£100 range will provide a user experience roughly equivalent to a standard desktop PC from 15 years ago. However, you can now expect a 4K display on many models, which would have been unthinkable then.