Embedded system Vs PC

The main difference between an embedded controller and a PC is that the embedded
controller is dedicated to one specific task or set of tasks. A PC is designed to run many
different types of programs and to connect to many different external devices. An
embedded controller has a single program and, as a result, can be made cheaply to
include just enough computing power and hardware to perform that dedicated task. A
PC has a relatively expensive generalized central processing unit (CPU) at its heart
with many other external devices (memory, disk drives, video controllers, network inter-face circuits, etc.). An embedded system has a low-cost micro controller unit (MCU) for its intelligence, with many peripheral circuits on the same chip, and with relatively few external devices. Often, an embedded system is an invisible part, or sub-module of another product, such as a cordless drill, refrigerator or garage door opener. The con-troller in these products does a tiny portion of the function of the whole device. The controller adds low-cost intelligence to some of the critical sub-systems in these devices.
An example of an embedded system is a smoke detector. Its function is to evaluate sig-
nals from a sensor and sound an alarm if the signals indicate the presence of smoke.
A small program in the smoke detector either runs in an infinite loop, sampling the sig-
nal from the smoke sensor, or lies dormant in a low-power “sleep” mode, being awake-
ened by a signal from the sensor. The program then sounds the alarm. The program
would possibly have a few other functions, such as a user test function, and a low bat-
tery alert. While a PC with a sensor and audio output could be programmed to do the
same function, it would not be a cost-effective solution (nor would it run on a nine-volt
battery, unattended for years!). Embedded designs use inexpensive micro controllers to put intelligence into the everyday things in our environment, such as smoke detectors, cameras, cell phones, appliances, automobiles, smart cards and security systems.