SCADA systems definitely fall under Embedded System as long as they are implemented with dedicated hardware which has a unique set of I/O interfaces (say sensors and actuators at dedicated ports, with designated memory maps etc) with the approprite control algotithm (P, PI, PD, PID, ON-OFF etc) embedded in the unit.

The above SCADA example you sited uses a ‘General Computing’ system tailored for a specific function. It uses a genaeral purpose hardware with a general purpose computing operating System. You can easily replace the hardware with a similar configuration general purpose computer as well as another operating system. Also you can use the same hardware for running another applications. In this case the SCADA application is running as a ‘soft’ware on top of a GPOS. It is not a ‘firm’ware. It is no way different from a ‘General Computing’ workstation/PC. The characteristics of embedded systems like application and domain specific hardware, uniquenes etc are not valid for this system. Another typical example is a POS machie running a general computing OS with generic PC h/w.

Embedded Computing Systems are way different from ‘General Computing Systems’ in terms of memory, processing capabilities, power consumption, operating conditions, response requirements etc….

The simplest (and, I think, best) definition I know is that an embedded system is anything that comes up running when you turn on the power. The sorts of systems mentioned here so far certainly fit the definition, and I have worked on plenty of such systems.

But I can also point to a SCADA system I worked on. It was hosted on a Dell dual-Xeon rackmount, running Windows Server 2003. The software was implemented as an autostart system service – to run the system, the only user interaction required was to turn on the power.

Does it qualify as ‘embedded’? I think it does. Your opinions?

If the answer is yes, you probably have a very sophisticated grandmother :^). However, the answer is almost certainly no – consider the humble hotel doorknob. Only an embedded guy knows it is an embedded system. If it does not look like a tower PC or laptop, the vast majority is clueless there is some smarts in the thing – including their cell phone.

Try this experiment: ask folks what percentage of microprocessors made every year end up in laptop and PCs – most will say 95% or greater (ignore the ‘microcontroller’ label because it doesn’t matter for the test, and some folks ‘know’ there is such a thing as ‘embedded systems’, although they are clueless about specifics). The real answer, as we know, is 0.5% to 2%, depending on the source and year.

@Shibu: While I agree with your general definition, I have to take issue with one minor point: WinCE is not an RTOS. There is nothing “real-time” about it – ‘soft’ time is being generous. My favorite RTOSs, BTW, are uCos and ThreadX.

Embedded systems are characterized by functionality, not choice of Operating systems, nor language, nor development technique.

A system is embedded if we don’t care about the software or the hardware but rather the totality.

It is not necessary that all embedded systems should contain an Operating System (Either RTOS or customized OS). It all depends on the nature, complexity and response requirement of the functions intented to fullfill by the embedded system. An embedded System can be one with a simple superloop control (All tasks executed repetedly in sequence in a single loop) or one with a Real Time Operating System like VxWorks, Windows CE, etc.. which implements different scheduling policies for task execution to provide real time response.

The demarcation between embedded computing and general purpose computing is shrinking with advent of latest h/w, processor and memory technologies. Embedded Systems were very constarined in terms of memory, processing, I/O capabilities etc in the olden days. Mobile handests are a typical examples for embedded devices which extends the general computing capabilities to the embedded space…

http://caminao.wordpress.com/what-is-to-be-represented/activities/real-time-activities/

These mega-embedded systems have something in common with traditional micro-embedded systems: the need for the computer system hardware and software designers to have a deep understanding of the application hardware (e.g., the missile or radar) and environment.

That is interesting from the point of view of classification, since now the bucket a particular system falls under is dependent on the users perception and/or the designers intent of the same. This would definitely decouple and untangle the discussions based on hardware and software platforms and types of engineers designing the systems etc. and we would have a relatively simple definition of what constitutes an embedded system. Simply; an embedded (computing(er)) system is a system who’s designers intent or users perception of it is not that of a computer.

Now if we take that as a starting point we could dive into the different kinds of embedded systems and work our way down to something that would make sense from a “work” perspective. Say for example terms like “deeply embedded” or small resource constrained embedded systems, display-less systems, user interactive systems etc…