Applications

Chassis Plans S6483 Single Board Computer Major Components

Single Board Computers are now commonly defined across two distinct architectures; no slots and slot support.

Embedded Single Board Computers are boards providing all the required I/O with no provision for plug-in cards. Applications are typically gaming (slot machines, video poker), kiosk, and machine control. Embedded Single Board Computers are much smaller than ATX motherboards, and provide an I/O mix more targeted to an industrial application such as on-board digital and analog I/O, on-board bootable flash so no hard drive is required, no on-board video, etc.

The term "Single Board Computer" now generally applies to an architecture where the Single Board Computer is plugged into a backplane to provide for I/O cards. In the case of PC104, the bus is not a backplane in the traditional sense but is a series of pin connectors allowing I/O boards to be stacked.

Single board computers are most commonly used in industrial situations where they are used in rackmount 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.

The primary advantage of ATX motherboards versus Single Board Computers is cost. Motherboards are manufactured by the millions for the consumer and office markets allowing tremendous economies of scale. Single Board Computers, on the other hand, are in a specialized market niche and are manufactured in much smaller numbers with the resultant higher cost. Motherboards and Single Board Computers now offer similar levels of feature integration meaning that a motherboard failure in either standard will require equivalent replacement.

The primary advantage of a PICMG Single Board Computer is the availability of backplanes offering virtually any slot configuration including legacy ISA support. Motherboards tend to the latest slot technology such that PCI slots are becoming legacy support with PCI-Express becoming the standard. In addition, motherboards offer, at most, 7 slots while backplanes can offer up to 20 slots. In a backplane 12.3" wide, similar in size to an ATX motherboard at 12", a backplane with a Single Board Computer can offer 12 slots for I/O cards with virtually any mix of slot types.

Types, standards

Currently the most common variety of Single Board Computer in use is of a specific form factor similar to other full-size 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, PCI-Express, etc), usually totaling 20 or less, meaning it will fit in a 19" rackmount enclosure (17" wide chassis).

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.

In the Intel Single Board Computer world, PICMG provides standards for the backplane interface: PICMG 1.0, 1.1 and 1.2^[1] provide for ISA and PCI support with 1.2 adding PCIX support PICMG 1.3^{[2] [3]} provides for PCI-Express support. Single Board Computers meeting the PICMG 1.3 specification are referred to as a System Host Board.

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.

Chassis Plans PICMG 1.3 Dual Quad Core Single Board Computer in BPX 3/8 Backplane

One of the first 10 MMD-1s, a prototype unit, produced by E&L Instruments in 1976. The "dyna-micro"/"MMD-1" was the world's first true "Single Board" computer. The MMD-1 had ALL components on a single Printed Circuit Board, including memory, I/O, user input device, and a display. Nothing external to the single board except power was required to both program and run the MMD-1. The original design of the MMD-1 was called the "dyna-micro", but it was soon re-branded as the "MMD-1"