Single-board computer
From Wikipedia, the free encyclopedia
Single-board computers (SBCs) are complete computers built on a single circuit board. The design is centered on a single microprocessor with RAM, IO and all other features needed to be a functional computer on the one board. The first true single-board computer was probably the MYCRO-1, built around an Intel 8080 CPU. SBCs also figured heavily in the early history of home computers, for example in the Acorn Electron and the BBC Micro.
With the development of PCs there was a sharp shift away from SBC, with computers being constructed from a motherboard, with functions like serial ports, disk drive controller and graphics being provided on daughterboards. Recently however this trend seems to have been reversed with motherboard manufacturers increasingly putting features such as sound, network, IO and even graphics built into the main board.
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[edit] Current SBCs
[edit] Applications
Single board computers are no longer widely used in personal computers (although there are some signs that this may change) but are most commonly used in industrial situations where they are used in rack-mount format for process control or embedded within other devices to provide control and interfacing. Because of the very high levels of integration, reduced component counts and reduced connector counts, SBCs are often smaller, lighter, more power efficient and more reliable than comparable multi-board computers. On the downside, this highly integrated nature means that upgrading of a single sub-system of an SBC is normally impossible, if there is a failure or an upgrade needed, the entire SBC normally has to be replaced.
[edit] Types, standards
Currently the most common variety of SBC in use is of a specific form factor similar to other plug-in cards and is intended to be used in a backplane. Some architectures are dependent entirely on single-board computers, such as CompactPCI, PXI, VMEbus, VXI, PICMG architecture, etc. In the Intel PC world, the intelligence and interface/control circuitry is placed on a plug-in board that is then inserted into a passive (or active) backplane. The end result is similar to having a system built with a motherboard, except that the backplane determines the slot configuration. Backplanes are available with a mix of slots (ISA, PCI, PCIX, etc), usually totaling 20 or less, meaning it will fit in a 19" rack mount enclosure.
Some single-board computers also exist as form factors that stack like building blocks, and do not have the form of a traditional backplane. Examples of stacking SBC form factors include PC/104, PC/104-Plus, PCI-104, EPIC, and EBX; these systems are commonly available for use in embedded control systems.
Stack-type SBCs often have memory provided on plug-cards such as SIMMs and DIMMs, however they can still be regarded as SBCs because although the memory modules are technically additional circuit boards, they have no extra functionality beyond providing memory and are basically just carriers for the RAM chips. Hard drive circuit boards are also not counted for determining if a computer is an SBC or not for two reasons, firstly because the HDD is regarded as a single block storage unit, and secondly because the SBC may not require a hard drive at all as most can be booted from their network connections.
