Today when we talk about single board computers we are normally speaking of an architecture in which I/O cards can be inserted into a backplane and the single board computer goes into the same backplane. The backplane is, essentially, the bus – the pathway around which commands and data pass – and a series of pin connectors can be substituted for the bus.
The current generation of single board computers is seen most often in process control (where they are likely to be rack-mounted) or as control and interface devices when embedded in other devices. Single board computers are generally more reliable than multi-board computers doing the same job as well as being smaller and lighter and cheaper to run (because they use less power).
However, single board computers have to compete with ATX motherboards which are usually cheaper because they are made in huge numbers whereas single board computers, designed to fill a particular niche, can’t offer anything like the same economies of scale in manufacture.
A typical configuration used in process control might consist of CPU, bootstrap PROMs, two serial I/O ports and three bidirectional parallel I/O ports together with 64KB of memory and a programmable real-time clock. This computer would connect with a supervisory or host computer and the clock will be programmed to generate a signal at a rate of 1 Hz so that the process measurements are read and control signals sent out once every second.
A suitable language for a configuration of the sort we have just described used in process control would be Pascal, although Basic was also in common use for general applications.
The single board computer would be configured and programmed to read a number of process measurements, perform the control algorithm and send out control signals. The SPC would also signal to the host any change in the control parameters.