Which of the following is a real time embedded system? Justify your answer (a) Ceiling Fan (b) Microwave Oven (c) Television Set (d) Desktop Key Board (e) Digital Camera

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(b) and (e) are embedded systems 

(a) Ceiling Fans: These are not programmable. 

(b) & (e) obey all definitions of Embedded Systems such as (i) Working in Real Time (ii) Programmable (iii) A number of systems coexist on a single platform to discharge one function(single functioned) 

(c) Television Set: Only a small part of it is programmable. It can work without being programmable. It is not tightly constrained. 

(d) Desktop Keyboard: Though it has a processor normally it is not programmable

Definition of Real Time Systems 
An operation within a larger dynamic system is called a real-time operation if the combined reaction- and operation-time of a task operating on current events or input, is no longer than the maximum delay allowed, in view of circumstances outside the operation. The task must also occur before the system to be controlled becomes unstable. A real-time operation is not necessarily fast, as slow systems can allow slow real-time operations. This applies for all types of dynamically changing systems. The polar opposite of a real-time operation is a batch job with interactive timesharing falling somewhere in between the two extremes. Alternately, a system is said to be hard real-time if the correctness of an operation depends not only upon the logical correctness of the operation but also upon the time at which it is performed. An operation performed after the deadline is, by definition, incorrect, and usually has no value. In a soft real-time system the value of an operation declines steadily after the deadline expires. 
Embedded System 
An embedded system is a special-purpose system in which the computer is completely encapsulated by the device it controls. Unlike a general-purpose computer, such as a personal computer, an embedded system performs pre-defined tasks, usually with very specific requirements. Since the system is dedicated to a specific task, design engineers can optimize it, reducing the size and cost of the product. Embedded systems are often mass-produced, so the cost savings may be multiplied by millions of items. 

Version 2 EE IIT, Kharagpur

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