The single board computer (SBC), a key product in the industrial PC industry, was originally designed for factories or special industrial control fields and focused on some very specific functions. However, the SBC has gradually expanded into commercial use, such as Point-of-sales (POS), KIOSK and Karaoke, as well as being used to support multi-media and Fast Ethernet.

What are SBCs.
    SBCs are complete computers built on a single circuit board. The design is centered on a single micro-processor with RAM, IO, and all other features needed for a functional computer, built on only one board. The first true SBC was probably the MYCRO-1, which was built around an Intel 8080 CPU. SBCs also figured heavily in the early home computers, for example in the Acorn Electron and the BBC Micro.

With the development of PCs, there was a sharp shift away from SBCs, with computers being constructed from a motherboard and having functions like serial ports, disk drive controllers, and graphics provided on daughterboards.

Nonetheless, this situation has now been reversed, with motherboard manufacturers increasingly building features such as sound, network, IO, and even graphics onto the main board.

The Embedded SBC Market
    Like the Big Board, the "Little Board" (Ampro, 1983) used a Z80 CPU and was targeted specifically at the CP/M operating system, but it was much smaller, about the size of a floppy disk drive (5.75x8.0 inches). Its unique combination of compactness, simplicity, reliability, and low cost made the Little Board practical and easy to embed commercial disk operating systems within devices that were not themselves computers.

Thus was born the embedded SBC market, which by now has become crowded with hundreds of SBC manufacturers producing thousands of different SBC products that target a vast array of embedded and dedicated computing applications.

Initially, every SBC product was completely unique---both architecturally and physically. This was largely due to the inherent diversity of embedded system requirements, combined with the wide assortment of processors and peripheral controllers that were available. Moreover, there were no standards to influence SBC developers' choices of functional and mechanical specs. But SBCs have gradually been expected to connect to systems and applications, and Taiwanese manufacturers have tended to develop total solutions.

PC-compatible SBCs
    By the mid 1980s, there was growing interest in IBM PC compatibility in embedded and other non-desktop applications, for two key reasons. First, PC chipset and peripherals compatibility enabled hardware systems to be produced that were lower cost, simpler, and easier to support. Second, PC compatibility made it possible to take advantage of the PC's operating systems (first MS-DOS, then Windows), languages, tools, and application software. Some of the resulting PC-compatible microcomputers were based on the form-factor of the IBM PC ("ISA bus") plug-in card. Others were implemented as standalone (non-backplane) systems on a single board. Still others were adaptations of popular industrial backplane buses (STD, VME).

In the case of embeddable non-backplane SBCs, the trend towards PC compatibility quickly became a stampede. Consensus also emerged around several popular form-factors:
* Little Board (5.75x8.0 inches): Complete systems on a single compact board, expandable with plug-on function modules.
* ISA "slot boards" (full-length, 13.8x4.8 inches; half-length, 7.1x4.8 inches): SBCs in the IBM PC plug-in card format which, though backplane-oriented, could also function as standalone SBCs (without backplanes).
* PC/104 modules (3.6x3.8 inches): Compact, rugged, self-stacking modules featuring a reliable pin-and-socket board-to-board expansion bus. With the coming of PCI, these were joined a decade later by PC/104-plus (PCI added to PC/104) and EBX (PC/104-plus added to Little Board).

Not all SBCs were built on the lines on these popular form-factors. Nor did they all go the PC-compatible (x86/DOS/Windows) route. Throughout the multi-decade history of SBCs, there have been, and continue to be, non-standard board sizes and processor architectures that target unique application requirements or fill niches not well matched to the standardized form-factors and popular “Wintel.(PC compatible) architecture.

Blowing Winds of Change
In recent years, several significant factors have seriously challenged the SBC market status.
* Exploding demand for embedded intelligence: Even the tiniest and least expensive products and devices have been expected to have at least rudimentary embedded intelligence. Many also require user-friendly graphical and/or speech interfaces.
* Ubiquitous connectivity: There has been a growing need for everything electronic to be interconnected, whether by wires or wireless. These devices must often be capable of inbound or outbound Internet connectivity and must support numerous standardized protocols (TCP/IP, PPP, HTTP, FTP).

* Evolving peripheral and bus interfaces: Although popular interconnection standards may sometimes have seemed everlasting, new interfaces have gradually supplanted the old. Nearly two decades after the birth of the PC, the ISA bus has finally been replaced by PCI, while USB has been replacing the venerable serial, parallel, and PS/2 ports. Ethernet has been everywhere and FireWire (IEEE-1394) has begun to make a strong showing. Meanwhile, SCSI never made it to the mainstream for PCs (other than Apples).
* Application-oriented system-on-chip processors: Numerous highly integrated ARM, MIPS, PowerPC, and x86 based one-chip systems have been developed to match the specifications of a wide array of high volume and cost sensitive appliance-like products. These "application-on-chip" processors represent tantalizing fodder for a new breed of high-integration, high-performance, and highly cost-effective SBCs.