The term Real-time is used in different domains among computer industry, and this adds to the general confusion. In the context of the Compact 2013 operating System, we are focusing on embedded systems where developers have to build control programs for automatic controlled devices. Other computing domains currently using the term Real-time include data processing and simulation but these obviously do not perform device control.

Computers have been used in embedded control systems since the mid 60’s; and this is when the term Real-time as we consider it came up in the literature. For a relatively long period, all embedded computers were specially crafted to fulfill their task, the hardware architectures was much simpler than today’s System-On-Chips (SOCs) and software libraries were reduced to the bare minimum. If we use the gearbox metaphor, these systems had a small numbers of tight gears. A large quantity of simple dedicated systems is still used nowadays, but most of them have a level of complexity which is below the scope of Compact 2013.

The Real-time embedded domain came up to a radical change during the 80’s as a consequence of the general evolution in computer’s industry. Standardization of both computers architectures and software libraries, combined with the generalization of networking and the continuous impact of downsizing had a strong influence on systems requirements and design. The number of functionalities required from an embedded machine literally exploded and design engineers had no other choices than using commercial off the shelf (COTS) solutions to meet project delivery schedule with an acceptable cost.

For obvious economic reasons, the lower cost COTS solutions generally are designed to serve the consumer market where hardware and software layers have to be flexible for original equipment manufacturers (OEMs) to easily adopt the same hardware platform to build wide range of devices while minimizing cost. As a consequence COTS solution generally do not offer the level of control required for embedded control systems, we could say that they are made of a large quantity of loose gears. The distinction between Hard Real-time and Soft Real-time came up during this period where COTS became largely used in control system, in other words nobody invented Soft Real-time as an alternative to Hard Real-time, some control systems allow for uncertainty as a tradeoff for price or time to market.

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