Simone Concepts

Defining Embedded Systems is HARD!

This is the question of the decade! Embedded systems have been around for years, and each of us owns a scad of them, but no agreed-upon definition exists! (Beware, a digression is impending, but with relevant references intermixed . . .)

A cheap and dirty definition:

"If it's got a plug or a charger, chances are it's an embedded system."

Here is my definition, which is similar with a few clarifications....with the idea that some brains need to be included.

"An embedded system is an electronic device like a cell phone, DVD player, or appliance that contains a special computer that only performs the programs needed to make that device work correctly."

...and the ubiquitous follow-on clarification...

"These computers are different from personal computers, which can perform a nearly endless array of user-selected programs like word processing, spreadsheets and email and photo editing programs. While most devices have only one embedded processor, others like cars contain many embedded processors to control individual tasks like windshield wiper delays, fuel injection, and antilock brake functions."

Whew! A mouthful. I know. Have you ever tried describing exactly what you do to your family and friends? And as you explain and reclarify you see their eyes glaze over? Defining embedded systems is tough - most descriptions don't tell what an embedded system is. They list characteristics of embedded systems, or indicate what an embedded system is not, and then provide examples of recognizable embedded systems in hope that the reader will have an ah-hah moment and connect the dots.

• "People use the term embedded system to mean any computer system hidden inside...products such as VCRs, digital watches, etc." David E. Simon, An Embedded Software Primer.

• "There is no general consensus about what an embedded system is nor is there a complete list of characteristic properties of such systems." Bas Graaf, Marco Lormans, and Hans Toetenel, Information Technology and Systems, Delft University of Technology, The Netherlands

Ha! Therefore we have free rein! Here is my favorite definition-by-description:

• "You already have a non-PC chip embedded in your car and stereo and rice cooker and phone. These chips are dumb chips, with limited ambitions. A chip in your car's brakes doesn't have to do floating-point math, spreadsheets, or video processing; it only needs to brake like a bulldog." New Rules for the New Economy, 10 Radical Strategies for a Connected World, by Kevin Kelly

Here are two decent definitions from the internet; a short one and a long one:

• "Embedded systems are tiny computers embedded in many kinds of products." Canadian Center for Occupational Health & Safety

• "An embedded system is a large or small computer system that is built into a product, a piece of equipment or another computer system, and that performs some task useful to the product, equipment or system. It is a computer system that is programmed to perform a particular task. This task may be very simple or very complex; that is not a relevant distinction. 'But' you say, 'all computers are programmed to perform tasks!' True, however an embedded system is programmed to perform its task from the time it is powered up until it is shut down. Its programming cannot be changed except in ways that its original programmer intended." The Innovations in Design Lab

Very few references actually shove a stake in the ground and provide a short-and-sweet working definition that is useful without clarification. One reason is that short-and-sweet "correct" definitions leave you wanting specifics. For example, these definitions are reasonable and they make sense to folks already in the embedded systems field, but can be rather cryptic for everyone else:

• "A computing device that performs a dedicated function." Microsoft Windows Embedded Developer Center

Personally, I am extremely hesitant to use a Microsoft-based operating system in a critical embedded device. Blue Screen of Death on my cell phone is annoying; Blue Screen of Death on my antilock brakes is somewhat less amusing.

• "Computers masquerading as non-computers." Stephen A. Edwards, Columbia University.

Cute. Has relevance and appeal. But what's it mean?

• "Any device that includes a programmable computer but is not itself a general-purpose computer." Charles J. Kim, Howard University.

Okay, but this assumes that the general populace knows what a general purpose computer it. "Is that like my Dell?" a friend asked me.

All true. All succinct. None terrifically enlightening.

Definition by Omission, Prevalence, or Invisibility

Sometimes it is easier to define something by describing what it is not.

• "Embedded systems do not provide standard computing services and normally exist as part of a bigger system." Sandeep Agrewal and Pankaj Bhatt

• "[D]evices other than desktop PCs, servers, and notebooks. " Tony Givargis, University of California, Irvine

Although this sounds flippant at first read, it is actually a reasonable definition by omission. As long as "device" means some electronic thing with some sort of smarts.

How many embedded systems or embedded computers do you have in your house? (Send me your counts!) We rely on these devices without fully understanding their prevalence or importance until the coffee pot fails to perk 10 minutes before the alarm clock goes off in the morning, or the smoke detectors all start chirping at 2AM for a battery change.

(Smoke detectors should not have a real time clock in them - but how do they know to start being incredibly annoying in the middle of the night? And that after you pull out the main 9V battery (that is supposedly near death), there is another little lithium cell hidden behind the "non user serviceable" seal?  And that it takes 2 layers of 5mm wetsuits and a suitcase piled on top of them in the basement to drown out the sound of the periodic chirps as you try to get back to sleep before you can wake up and drive to the store to purchase 7 new 9V batteries for every detector in the house because when one chirps they all chirp?)

On a 10 minute walk through my house, I found 202 embedded devices - now this is just whole devices, not individual embedded processors. For example, I counted both my car and my cell phone as single embedded devices, although my car could have over 100 embedded processors in it and my phone has about 3. 

• "These systems are invisible to us but they shape our world." The Innovations in Design Lab
• "Embedded systems . . . are called 'embedded' because they are an integral component of the device's ability to function and are not always readily visible to the untrained eye." Gary North, Gary North Online
• "Embedded systems pervade every aspect of life, often going unnoticed to the end user while at the same time enabling new activities, even a new quality of life." Prof. Mariagiovanna Sami, ALaRI Scientific Director, University of Lugano
• "A large organization could have hundreds of thousands of embedded systems. Because embedded systems are so pervasive, they can stop your business from functioning before you even know that they exist." Gary North, Gary North Online
• "The number of processors in embedded systems already exceeds the number of processors in PCs, and this trend is expected to continue." Embedded System Design by Peter Marwedel, University of Dortmund published by Kluwer Academic Publishers
• "Only 2% of the world's microprocessors run on traditional desktops and servers." Ken Klein, CEO, Wind River Systems

Definition by Prophesy

As a dear friend of mine would say, "You are an engineer and engineers just make gadgets."  Nip tirade in the bud right there. Well, dear, your life REVOLVES around gadgets, so deal. Gadgets used to be little disconnected thingies that did some little interesting functions that appealed to early adopters and Star Trekkie types.  Welcome of the new millennium where these little gadgets are all starting to talk to one another and provide a new backbone of communications and information.

• "Embedded systems can be defined as information processing systems embedded into enclosing products such as cars, telecommunication or fabrication equipment. Such systems come with a large number of common characteristics, including real-time constraints, and dependability as well as efficiency requirements. Following the success of information technology (IT) for office and workflow applications, embedded systems are considered to be the most important application area of IT during the coming years. [emphasis added]" Prof. Mariagiovanna Sami, ALaRI Scientific Director, University of Lugano

...This is a excellent term, "enclosing product," that appears only about 5 times in Google (as of 2/2/3005) as a noun in this context...perhaps a new term is being coined?  Here it is again:

• "Embedded systems are information processing systems that are embedded into an enclosing product. Examples of embedded systems include information processing systems in transportation, telecommunication, manufacturing and medical applications. ... According to many predictions, embedded systems will be the main market of information technology in the future." from Embedded System Design by Peter Marwedel.

And then the government always has to get involved. . . Here's an amusing thought: the lack of a formal definition for "embedded systems" has even been sent to a committee that provides advice to the federal government.

• "[The board] will assemble a study committee of approximately 12 members . . . It will then convene a series of meetings and small workshops . . . the committee will attempt to answer questions such as: What are embedded systems? How do they differ from more traditional computing systems?"The National Academies.  (Okay, I avoided the main focus of the committee work, which is to study networked embedded systems, but you get the idea when the first question is to define what the base technology is!)

On the other hand, the National Science Foundation is offering federal grants for embedded systems projects, recognizing the future role of embedded systems in information technology:

• Embedded and hybrid systems: The National Science Foundation solicits proposals for the embedded and hybrid systems program through the division of computer-communications research. This program supports fundamental research in embedded systems, emphasizing the role of information technology, specifically embedded software, as an active element in control, diagnosis, and decision support for physical and engineered systems. Embedded systems combine interacting elements:
• the temporal-spatial properties and continuous dynamics of the physical system to be monitored or controlled;
• the concurrency, real-time, and synchronization properties and resource demands of software that controls the system;
• characteristics and services of the computational platform (both hardware and system software).

Some Other Definitions

• "Any system where the user doesn't want to know that it includes a processor." Dr. Doug Locke, Locke Consulting, LLC, www.doug-locke.com.
• "An embedded system is a mixed hardware / software system dedicated for a specific application and is part of and reactive to a larger, physical system to which it is at least logically connected." Bas Graaf, Marco Lormans, and Hans Toetenel, Information Technology and Systems, Delft University of Technology, The Netherlands
• "An embedded system is an information processing system that responds to externally generated input stimuli within a finite and specified period." Gul N. Khan, Ryerson University
• "Computers purchased as a part of some other piece of equipment."Philip Koopman, Carnegie Melon University.