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Definition of an Embedded System

So far, you have a general understanding of embedded systems from the examples given. But what is the embedded system? Currently, there are different concepts for embedded system in the industry.

According to the Institution of Engineering and Technology (IET), embedded systems are devices used to control, monitor, or assist the operation of equipment, machinery, or plants. Smartphones, as an important sector of embedded systems, have the following characteristics:

Limited Resources

The majority of embedded systems have extremely limited resources. On one hand, the resources referred to here are hardware resources, including computing speed and processing capability of the CPU, size of the available physical memory, and capacity of the ROM or flash memory that stores code and data. On the other hand, resources are also the functions provided by the software. Compared with general operating systems, embedded operating systems have comparatively simple functions and structure.

Embedded systems' resource constraints lead to designs that are sufficient, instead of powerful.

Real-Time Performance

The real-time aspect of embedded systems means tasks must usually be executed in a certain, predictable amount of time, and maximum execution time limits must

be ensured.

Real time is divided into soft real time and hard real time. Soft real time has lessstringent requirements; even if the time limit cannot be met in some cases, it won't have a fatal impact on the system. For example, a media player system is soft real time. The system is supposed to play 24 frames in one second, but it is also acceptable when the system fails in some overloaded conditions. Hard real time has strict requirements.

The execution of tasks must be absolutely ensured in all situations; otherwise the consequences will be catastrophic. For example, aircraft autopilot and navigation system are hard real-time systems. They must accomplish a specific task within the certain time limit; otherwise a major accident, collision, or crash could occur.

Many embedded systems (mobile phones, game consoles, and so on) do not need real-time guarantees. But real time is the key for some embedded systems, such as a steel-rolling system in a large steel mill and the real-time alarm system in a large electrical substation. In these applications, the system must respond to a specific signal at a given time.

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