When I hear that, I always think about an mobile device. But why is the hardware "embedded" there? Isn't the whole device the hardware? Why is a personal computer no embedded hardware system?
In today's world embedded simply refers to a system with one or more of the following traits:
Single purpose (ie, not a general purpose computer, like your desktop)
Firmware rather than software - still software, but not as easily updated (flash, etc)
Hardware and software are designed together as a unit
Different, perhaps more rigorous testing as software updates are not desired
Real time computing
Memory integrated on the CPU
Microcontroller rather than microprocessor
Expected high reliability (you shouldn't have to reboot your dishwasher or microwave)
If it runs a program, but doesn't look like a computer, it's an embedded system.
That's my standard answer for friends and family. There's too many different types of embedded systems to get more specific.
I worked in the "embedded" area for a while and we considered anything that we had to write custom code for the hardware to be embedded.
If you have to work around the memory structure, write custom device drivers and anything that sits "directly on the metal" is generally "embedded".
If you're debugging it via a serial port - it's embedded.
It is called "embedded" because the computer is embedded as part of a larger device.
There is a very wide range of embedded systems.
At the low end are 8-pin PICs, for example there is a 12F629 in these diode lights. These costs cents and have very little memory.
The NXT by LEGO contains two controllers, a relatively big AT91SAM7S256 with a 32-bit ARM core, 256KB of flash ROM and 64KB of RAM, and a smaller 8-bit ATmega48 with 4KB of flash.
Currently I'm working on embedded systems for trains, these typically have a PowerPC with some hundreds of MHz clock, on the order of a hundred MB of RAM, run VxWorks or Linux and are connected by Ethernet.
I think there are still more powerful embedded systems for telecommunications, but I haven't worked on these.
As per Wikipedia:
An embedded system is a
special-purpose computer system designed to perform one or a few
dedicated functions, often with
real-time computing constraints. It is
usually embedded as part of a complete
device including hardware and
mechanical parts. In contrast, a
general-purpose computer, such as a
personal computer, can do many
different tasks depending on
programming.
Embedded systems are designed to do some specific task, rather than be a
general-purpose computer for multiple
tasks. Some also have real-time
performance constraints that must be
met, for reasons such as safety and
usability; others may have low or no
performance requirements, allowing the
system hardware to be simplified to
reduce costs.
Embedded systems are not always standalone devices. Many embedded
systems consist of small, computerized
parts within a larger device that
serves a more general purpose. For
example, the Gibson Robot Guitar
features an embedded system for tuning
the strings, but the overall purpose
of the Robot Guitar is, of course, to
play music.[2] Similarly, an embedded
system in an automobile provides a
specific function as a subsystem of
the car itself.
The program instructions written for embedded systems are referred to as
firmware, and are stored in read-only
memory or Flash memory chips. They run
with limited computer hardware
resources: little memory, small or
non-existent keyboard and/or screen.
From personal experience, if it's "headless" (i.e. doesn't have an output device like a VDU and relies on something like LED's), if there is a serial port used mainly for debugging and logging and if you often use a logic analyser for debugging, it's embedded.
"Embedded" has become a very diverse term.
I've seen and worked on designs that:
Simply toggled discrete I/O (including LEDs) at fixed intervals
Drivers for hardware solutions (e.g. webcams, wireless com)
Acted as communications translators for board-level I/O (SPI<->I2C<->Rs232<->USB)
[ insert multitude of appliances here ]
Human-controlled electronics (calculator-esque, phone-esque)
System level devices to coordinate actions of other devices.
I also like Dour-High-Arch's comment above:
"Another important difference is that embedded apps may run for years without intervention..."
"Embedded system" is a very broad term and I don't think that it is easy to have a single definition. The word "embedded" actually refers to an industry and not to a "hardware system". The description of embedded systems has changed over the years and it is definitely going to change in the future too.
In early days one would say the embedded systems were only programmed in assembly, but now C is common place and perhaps in the future other languages are used as well. CPUs are getting bigger and bigger, external memories are used all the time and they are many devices considered to be embedded that are not dedicated to a single task, applications can be added to them and the software is easily updated. Watches, gadgets, house appliances, automotive devices, PLCs, motor controllers, weather stations, system monitoring devices are all considered embedded. It is difficult to singe define them all.
Related
What is the connection between microprogramming and embedded systems?
Is microprogramming a machine language?
Microprogramming it is the same as microcode?
Are embedded systems manufactured using microprogramming only?
Or isn't it an exclusivity of an embedded system that is using microprogramming?
If possible, please exemplify. Thanks!
Microprogramming / microcoding is an implementation technique for processors — as such dates back pretty far.
A processor implements an instruction set; programs using these instructions are generated by a compiler or assembly language programmer and stored in program files, later loaded into memory to execute the program.
A microcoded processor is like having another, different processor-within-the-processor that is used to interpret the instruction stream (sequences of machine language) of the program. This processor within the processor has its own instructions set and its own program. Unlike the externally visible instruction set (which can load & run any program), the processor within the processor generally only runs one dedicated program (the instruction set interpreter), which is stored in a ROM (or re-writable flash) inside the processor.
(In some such systems, the processor within the processor has instructions that are very wide (as in horizontal microcode), and impractical (regarding code size) for general use by regular programs.)
What is the connection between microprogramming and embedded systems?
There is no particular relationship between microcoding and embedded. Yes/no on either can be mixed with each other.
Is microprogramming a machine language?
Yes, I would say it is, but it is generally not accessible to operating systems and user programs.
Microcoding was particularly popular when virtually all instructions each executed in multiple cycles. Later techinques removed the indirection of the microcoded machine in favor of direct hardwired execution, with single cycle approaches. This publication sheds some light on some of the thinking of the day during the transition of the state of the art from microcoding to hard wiring. See also IBM 801.
Most processors these days are not microprogrammed; however, the very advanced techniques applied by x86 processors may mimic microprogramming techniques here and there.
Embedded systems are simply processors used in devices that are not seen as "computers", for example, a thermostat, a microwave, or a car (which might have numerous embedded systems). Considerations here are that these systems are dedicated: they tend to run a single program (rather than running an operating system capable of running any program the user directs); they have low power requirements, disconnected requirements (disconnected from user terminal/screen/keyboard, perhaps from network, etc..). Still, embedded system keep getting even more powerful.
my question is : how can build single board computer like Raspberry Pi for run OS ?
user ARM micro processor and debian arm os , can use USB and etc.
like raspberry pi and other single board computer
i search but find nothing for help me !!! :(
The reason you can find nothing is probably because it is a specialist task undertaken by companies with appropriate resources in terms of expertise, equipment, tools and money.
High-end microprocessors capable of running an OS such as Linux use high-pin-density surface mount packages such as BGA or TQFP, these (especially BGA) require specialist equipment to manufacture and cannot reliably or realistically be assembled by hand. The pin count and density necessitates the use of multi-layer boards, these again require specialist manufacture.
What you would have to do if you wanted your own board, is to design your board, source the components, and then have it manufactured by a contract electronics assembly house. Short runs and one-off's will cost you may times that of just buying a COTS development or application board. It is only cost-effective if you are ultimately manufacturing a product that will sell in high volumes. It is only these volumes that make the RPi so inexpensive (and until recently Chinese manufacture).
Even if you designed and had your own board built, that in itself requires specialist knowledge and skill. The bus speeds on such processors require very specific layout to maintain signal integrity and timing and to avoid EMC problems. The cost of suitable schematic capture and board layout software might also be prohibitive, no doubt there are some reasonably capable open source tools - but you will have to find one that generates output your manufacturer can use to set-up their machinery.
Some lower-end 8 bit microcontrollers with low pin count are suitable for hand soldering or even DIP socketing, using a bread-board or prototyping board, but that is not what you are after.
[Further thoughts added 14 Sep 2012]
This is probably only worth doing if one or more of the following are true:
Your aim is to gain experience in board design, manufacture and bring-up as an academic or career development exercise and you have the necessary financial resources.
You envisage high production volumes where the economies of scale make it less expensive than a COTS board.
You have product requirements for specific features or form-factor not supported by COTS boards.
You have restricted product requirements where a custom board tailored to those and having no redundant features might, in sufficient volumes be cost-effective.
Note that COTS boards come in two types: Application modules intended for integration in a larger system or product, and development boards that tend to have a wide range of peripherals, switches, indicators and connectivity options and often a prototyping area for your own use.
I know this is an old question, but I've been looking into the same thing, possibly for different reasons, and it now comes up at the top of a google search providing more reasons not to ask or even look into it than it provides answers.
For an overview of what it takes to build a linux running board from scratch this link is incredibly useful:
http://hforsten.com/making-embedded-linux-computer.html
It details:
The bare minimum you need in terms of hardware ( ARM processor, NAND flash etc )
The complexities of getting a board designed
The process of programming the new chip on the board to include bootloaders and then pointing them to a linux kernel for the chip to boot.
Whether the OP wishes to pursue every or just some of these challenges, it is useful to know what the challenges are.
And these won't be all of them, adding displays, graphics and other hardware and interfaces is not covered, but this is a start.
Single board computers(SBC) are expected to take more load than normal hobby board and so it has slightly complicated structure in terms of PCB and components. You should be ready to work with BGA packages. Almost all of processors in SBCs are BGA (no DIP/QAFP). Here is the best blogpost that I recently came across. Its very nicely designed and fabricated board running Linux on ARM processor. Author has really done a great job at designing as well as documenting the process. I hope it helps you to understand both hardware and software side of SBCs.
A lot of answers are discouraging. But, I would say you can do it, as I have done it already with imx233. Its not easy, its not a weekend project. My project link is MyIMX233.
It took me about 4-5months
It didn't cost me much, a small fine tip soldering iron is what I used.
The hard part is learning to design PCB.
Next task would be to find a PCB manufacturer with good enough precision, and prototyping price.
Next task would be to source components.
You may not get it right, I got the PCB right by my 3rd iteration. After that I was able to repeatedly produce 3 more boards all of which worked fine.
PCB Design - I used opensource KiCAD. You need to take care in doing impedance matching between RAM and processor buses, and some other high speed buses. I managed to do it in 2 layer board with 5mil/5mil trace space.
Component Sourcing - I got imx233 LQFP once via mouser, and once via element14.
RAM - 64MB tssop.
Soldering - I can say its easy to mess up here, but key is patience. And one caution don't use frying pan and solder past to do reflow soldering. I literally fried my first 2 processors like this. Even hot air soldering by a mobile repair shop was also not good enough.
Boot loading image - I didn't take much chance here, just went with Archlinux image by olimex.
If you want to skip the trouble of circuit designing between RAM & processor, skip imx233 and go for Allwinner V3S. In 2017/2018 this would be easiest approach.
Bottom line is I am a software engineer by profession, and if I can do it, then you can do it.
Why not using an FPGA board?
Something with Zynq like the Zybo board or from Altera like the DE0-Nano SoCKit.
There you already have the ARM core, memory, etc... plus the possibility to add the logic you miss.
What is mean by embedded system?
If a system/machine or product which we are making is for multiple purposes, then can we consider it as an embedded system? Or is it that only a system dedicated for a particular task that is considered as an embedded system? Can a PC/mobile/laptop be considered as an embedded system or not?
Generally an embedded system is one placed into operation for a specific, narrow purpose, and lacking the kind of general purpose user interfaces you would find on an ordinary desktop/laptop.
That is not to say though that an embedded system cannot have these - I've seen test equipment such as network analyzers running desktop operating systems, with mouse/keyboard ports. One could probably hack one of those to use it for general purpose computing, but it would not be cost effective.
Going the other way, you can take a general purpose computer and shove it into an embedded application. However, systems optimized for embedded use may be more robust, support better real-world I/O (often retaining legacy ports), and use parts expected to be available over longer lifetimes than used in commodity PCs (if one fails, you want to be able to replace it with the exact same thing).
Often embedded systems are smaller - 8 bit processors (even 4-bit or serial-core historically) with limited memory; though 32 bit cores such as the arm family are now inexpensive and commonplace. Nor are tens to hundreds of megabytes of memory unknown.
Older cellphones would have a lot in common with embedded systems, but rather obviously contemporary smartphones are catching up in power and versatility, though still often constrained by user interface. Software wise some "think small" habits endure - for example, Android's compact bionic C library and toolbox shell have similar design goals to embedded C libraries and busybox. In other ways though, expansive resource-gobbling user experiences are now the norm on phones. Toss tablets based on the same processors and accessorized with keyboard into the mix, run a kernel designed originally for desktop computers on them, and the real difference is between UI software stacks designed to run segregated "apps" on a touch interface, vs one designed to run more traditional programs.
This is a question that even embedded systems experts often ask and discuss. There is as with many things a spectrum, and simple definitions are difficult.
My preferred definition is: a system containing one or more computing or processing element that is not a general purpose computer.
Some systems are inarguably embedded within that definition, and include such things as washing machine controllers, telephone switches, satellite navigation equipment, marine chart-plotters, automotive ECUs, laser printers etc.
Some are less easily categorised. A first generation digital mobile phone, is probably certainly an embedded system while more modern feature and smart phones however are somehow different. They can run apps chosen and installed by end-users allowing them to perform tasks not determined by the manufacturer. With increasing capabilities they are essentially hand-held computers and the range of apps sufficient to be able to regard them as "general purpose".
With these more ambiguous systems, it is useful to ask perhaps not what is an embedded system, but rather what is embedded systems development? For example, the manufacturer of your smart-phone deployed on it an operating system, the signal processing and communications stack required for it to operate as a telephone, all the device drivers and stacks for WiFi, USB, data storage etc., and this is certainly embedded systems development. However the guys writing apps for PlayStore or AppStore etc. are writing to a defined common platform abstracted by all that embedded code - that is not embedded systems development by any definition that I would accept, unless perhaps the application were for some bespoke vertical market application - like the delivery signature apps UPS drivers have on PDAs for example - in that environment the "general-purpose" device has been re-purposed as a "special-purpose" device.
With respect to a PC; a PC can be the embedded computing element in a system that is not a general purpose computer. Industrial PCs are commonly found embedded in manufacturing and packaging machinery, CNC machine tools, medical equipment etc. Although they share hardware architecture with desktop PCs they do not necessarily look like desktop PCs and come in many different form factors of both boards, and enclosures. Even within a desktop PC however, there are many examples of embedded computing elements, and embedded software such as the BIOS responsible for bootstrapping the system, the keyboard controller and disc drive controllers for example.
An embedded system is any electronic system that uses a CPU chip, but that is not a general-purpose workstation, desktop or laptop computer.
An embedded system is a special-purpose computer system designed to perform a dedicated function. Unlike a general-purpose computer, such as a personal computer, an embedded system performs one or a few pre-defined tasks, usually with very specific requirements, and often includes task-specific hardware and mechanical parts not usually found in a general-purpose computer.
Read more: http://romux-loc.com/tutorials/embedded-system#ixzz3113gchPt
Embedded system are devices that do some specific job not like our laptops which can play music, click pictures and format documents. They are devices like water filter , washing machines, vending machine etc.
They are programmed for some specific work and they do that work in a super loop depending on the user input.Like the vending machine always perform same thing when you opt for coffee in it with the help of button provided in it.
So in that way mobile phone is not an embedded system because it has no super loop and it can do various general purpose things just like a computer.
An embedded system has memory constrain, timing constrain and they do things in limited space.
Embedded system is any device that includes a programmable computer put it is not itself a general-purpose computer, so the mobile is not an embedded system because it has no super loop and it can do various general purpose things just like a computer, and an embedded system has memory constrain timing, constrain and they do things in limit space.
The embedded system is a microprocessed system in which a computer is attached to the system it controls. An embedded system can perform a set of tasks that have been predefined. The system is used for specific tasks, and thus, through engineering it is possible to optimize a given product and decrease the size, as well as the computational resources and its final value.
Embedded systems are all around us, and for that reason, we are not aware of their computational capacity, since we are so involved with such mechanisms. Embedded systems operate on machines that can work for several years without stopping, and which still, in some cases, have the ability to self-correct.
An excellent example of items that use embedded systems are the famous smartphones, which perform specific functions, and which have more limited mechanisms than computers.
Check below a list with some examples that receive the application of embedded systems:
Electronic ballot box
Video games
Calculators
Printers
Hospital equipment
In vehicles
Some home appliances
Cellular apparatus
Routers
A definition that may help to get the difference.
An embedded system can be considered as a system with which another embedded system cannot be developed. So presently, using a mobile phone, one cannot develop an 'embedded system'. If it is possible by the mobile device, then it should be considered as a general purpose system.
An example of an "embedded system" is a chip that is inserted underneath a dog's skin for identification purposes. Words like "embedded system" have specific meanings that only specialists understand. Such ambiguities make understanding technical language difficult for ordinary people.
embedded (ɪmˈbɛdɪd)
adj
fixed firmly and deeply in a surrounding solid mass
constituting a permanent and noticeable feature of something
(Journalism & Publishing) journalism assigned to accompany an active military unit
(Grammar) grammar inserted into a sentence
(Computer Science) computing (of a piece of software) made an integral part of other software
I am new to the locating hardware side of embedded programming and so after being completely overwhelmed with all the choices out there (pc104, custom boards, a zillion option for each board, volume discounts, devel kits, ahhh!!) I am asking here for some direction.
Basically, I must find a new motherboard and (most likely) re-implement the program logic. Rewriting this in C/C++/Java/C#/Pascal/BASIC is not a problem for me. so my real problem is finding the hardware. This motherboard will have several other devices attached to it. Here is a summary of what I need to do:
Required:
2 RS232 serial ports (one used all the time for primary UI, the second one not continuous)
1 modem (9600+ baud ok) [Modem will be in simultaneous use with only one of the serial port devices, so interrupt sharing with one serial port is OK, but not both]
Minimum permanent/long term storage: Whatever O/S requires + 1 MB (executable) + 512 KB (Data files)
RAM: Minimal, whatever the O/S requires plus maybe 1MB for executable.
Nice to have:
USB port(s)
Ethernet network port
Wireless network
Implementation languages (any O/S I will adapt to):
First choice Java/C# (Mono ok)
Second choice is C/Pascal
Third is BASIC
Ok, given all this, I am having a lot of trouble finding hardware that will support this that is low in cost. Every manufacturer site I visit has a lot of options, and it's difficult to see if their offering will even satisfy my must-have requirements (for example they sometimes list 3 "serial ports", but it appears that only one of the three is RS232, for example, and don't mention what the other two are). The #1 constraint is cost, #2 is size.
Can anyone help me with this? This little task has left me thinking I should have gone for EE and not CS :-).
EDIT: A bit of background: This is a system currently in production, but the original programmer passed away, and the current hardware manufacturer cannot find hardware to run the (currently) DOS system, so I need to reimplement this in a modern platform. I can only change the programming and the motherboard hardware.
I suggest buying a cheap Atom Mini-ITX board, some of which come with multi - 4+ RS232 ports.
But with Serial->USB converters, this isn't really an issue. Just get an Atom. And if you have code, port your software to Linux.
Here is a link to a Jetway Mini-Itx board, and a link to a 4 port RS232 expansion module for it. ~$170 total, some extra for memory, a disk, and a case and PSU. $250-$300 total.
Now here is an Intel Atom Board at $69 to which you could add flash storage instead of drives, and USB-serial converters for any data collection you need to do.
PC104 has a lot of value in maximizing the space used in 19" or 23" rackmount configurations - if you're not in that space, PC104 is a waste of your time and money, IMHO.
The BeagleBoard should have everything you need for $200 or so - it can run Linux so use whatever programming language you like.
A 'modern' system will run DOS so long as it is x86, I suggest that you look at an industrial PC board from a supplier such as Advantech, your existing system may well run unchanged if it adheres to PC/DOS/BIOS standards.
That said if your original system runs on DOS, the chances are that you do not need the horsepower of a modern x86 system, and can save money by using a microcontroller board using something fairly ubiquitous such as an ARM. Also if DOS was the OS, then you most likely do not need an OS at all, and could develop the system "bare-metal". The resources necessary just to support Linux are probably far greater than your existing application and OS together, and for little or no benefit unless you intend on extending the capability of the system considerably.
There are a number of resources available (free and commercial) for implementing a file system and USB on a bare-metal system or a system using a simple real-time kernel such as FreeRTOS or eCOS which have far smaller footprints than Linux.
The Windows embedded site ( http://www.microsoft.com/windowsembedded/en-us/default.mspx )
has a lot of resources and links to hardware partners, distributors and development kits. There's even a "Spark" incubation project ( http://www.microsoft.com/windowsembedded/en-us/community/spark/default.mspx )
What's also really nice about using windows ce is that it now supports Silverlight as a development environment.
I've used the jetway boards / daughter cards that Chris mentioned with success for various projects from embedded control, my home router, my HTPC front end.
You didn't mention what the actual application was but if you need something more industrial due to temperature or moisture constraints i've found http://www.logicsupply.com/ to be a good resource for mini-itx systems that can take a beating.
A tip for these board is that given your minimal storage requirements, don't use a hard drive. Use an IDE adapter for a compact flash card as the system storage or an SD card. No moving parts is usually a big plus in these applications. They also usually offer models with DC power input so you can use a laptop like or wall wart external supply which minimizes its final size.
This http://www.fit-pc.com/web/ is another option in the very small atom PC market, you'd likely need to use some USB converters to get to your desired connectivity.
The beagle board Paul mentioned is also a good choice, there are daughter cards for that as well that will add whatever ports you need and it has an on board SD card reader for whatever storage you need. This is also a substantially lower power option vs the atom systems.
There are a ton of single board computers that would fit your needs. When searching you'll normally find that they don't keep many interface connectors on the processor board itself but rather you need to look at the stackable daughter cards they offer which would provide whatever connections you need (RS-232, etc.). This is often why you see just "serial port" in the description as the final physical layer for the serial port will be defined on the daughter card.
There are a ton of arm based development boards you could also use, to many to list, these are similar to the beagle board. Googling for "System on module" is a good way to find many options. These again are usually a module with the processor/ram/flash on 1 card and then offer various carrier boards which the module plugs into which will provide the various forms of connectivity you need.
In terms of development, the atom boards will likely be the easiest if your more familiar with x86 development. ARM is strongly supported under linux though so there is little difficulty in getting these up and running.
Personally i would avoid windows for a headless design like your discussing, i rarely see a windows based embedded device that isn't just bad.
Take at look at one of the boards in the Arduino line, in particular the Arduino Mega. Very flexible boards at a low cost, and the Mega has enough I/O ports to do what you need it to do. There is no on-chip modem, but you can connect to something like a Phillips PCD3312C over the I2C connector or you can find an Arduino add-on board (called a "shield") to give you modem functionality (or Bluetooth, ethernet, etc etc). Also, these are very easy to connect to an external memory device (like a flash drive or an SD card) so you should have plenty of storage space.
For something more PC-like, look for an existing device that is powered by a VIA EPIA board. There are lot of devices out there that use these (set-top boxes, edge routers, network security devices etc) that you can buy and re-program. For example, I found a device that was supposed to be a network security device. It came with the EPIA board, RAM, a hard drive, and a power supply. All I had to do was format the hard drive, install Linux (Debian had all necessary drivers already included), and I had a complete mini-computer ready to go. It only cost me around $45 too (bought brand new, unopened on ebay).
Update: The particular device I found was an EdgeSecure i10 from Ingrian Networks.
ASIDE: Yes, this is can be considered a subjective question, but I hope to draw conclusions from the statistics of the responses.
There is a broad spectrum of computing devices. They range in physical sizes, computational power and electrical power. I would like to know what embedded developers think is the determining factor(s) that makes a system "embedded." I have my own determination that I will withhold for a week so as to not influence the responses.
I would say "embedded" is any device on which the end user doesn't normally install custom software of their choice. So PCs, laptops and smartphones are out, while XM radios, robot controllers, alarm clocks, pacemakers, hearing aids, the doohickey in your engine that regulates fuel injection etc. are in.
You might just start with wikipedia for a definition
http://en.wikipedia.org/wiki/Embedded_system
"An embedded system is a computer system designed to perform one or a few dedicated functions, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. "
Coming up with a concrete set of rules for what an embedded system is is to a large degree pointless. It's a term that means different things to different people -maybe even different things to the same people at different times.
There are some things that are pretty much never considered an embedded system, for example a Windows Desktop machine. However, there are companies that put their software on a Windows box - even a bog standard PC (maybe a laptop) - set things up so their application loads automatically and hides the desktop. They sell that as a single purposed machine that many people would call an embedded system (but many people wouldn't). Microsoft even sells a set of tools called Embedded Windows that helps enable these kinds of applications, though it's targeted more to OEMs who will customize the system at least somewhat instead of just putting it on a standard PC. Embedded Windows is used for things like ATM machines and many other devices. I think that most people would consider an ATM an embedded system.
But go into a 7-11 with an ATM that has a keyboard (I honestly don't know what the keyboard is for), press the right shift key 5 times and you'll get a nice Windows "StickyKeys" messagebox (I wonder if there's an exploit there - I sure hope not). So there's a Windows system there, just hidden and with some functionality removed - maybe not as much as the manufacturer would like. If you could convince it to open up notepad.exe somehow does the ATM suddenly stop being an embedded system?
Many, many people consider something like the iPhone or the iTouch an embedded system, but they have nearly as much functionality as a desktop system in many ways.
I think most people's definition of an embedded system might be similar to Justice Potter Stewart's definition of hard-core pornography:
I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it...
I consider an embedded system one where the software is rarely developed directly on the target system. This definition includes sophisticated embedded systems like the iPhone, and excludes primitive desktop systems like the Commodore 64. Not having the development tools on the target means you have to add 'reprogram device' to the edit-compile-run cycle. Debugging is also made more complicated. This encompasses most of the embedded "feel."
Software implemented in a device not intended as a general purpose computing device is an "embedded system".
Typically the system is intended for a single purpose, and the software is static.
Often the system interacts with non-human environmental inputs (sensors) and mechanical actuators, or communication with other non-human systems.
That's off the top of my head. Other views can be read at this embedded.com article
Main factors:
Installed in a fixed place somewhere (you can't carry the device itself around, only the thing it's built into)
The run a long time (often years) with little maintenance
They don't get patched often
They are small, use little power
Small or no display
+1 for a great question.
Like many things there is a spectrum.
At the "totally embedded" end you have devices designed for a single purpose. Alarm clocks, radios, cameras. You can't load new software and make it do something else. THere is no support for changing the hardware,
At the "totally non-embedded" end you have your classic PCs where everything, both HW and SW, can be replaced.
There's still a lot in between those extremes. Laptops and netbooks, for example, have minimally expandable HW, typically only memory and hard disk can be upgraded. But, the SW can be whatever you want.
My education was as a computer engineer, so my definition of embedded is hardware oriented. I draw the line at the MMU (memory management unit). If a chip has an MMU, it usually has off-chip RAM and runs an OS. If a chip does NOT have an MMU, it usually has on-board RAM and runs an RTOS, microkernel or custom executive.
This means I usually dismiss anything running linux, which is shortsighted. I admit my answer is biased towards where I tend to work: microcontroller firmware. So I am glad I asked this question and got a full spectrum of responses.
Quoting a paragraph I've written before:
An embedded system for our purposes is
a computer system that has a specific
and deterministic
functionality\cite{LamieReal}.
Typically, processors for embedded
systems contain elements such as
onboard RAM, special-purpose
processing elements such as a digital
signal processor, analog-to-digital
and digital-to-analog converters.
Since the processors have more
flexibility than a straightforward
CPU, a common term is microcontroller.