What is Embedded System

Embedded system employs a combination of software & hardware to    perform a specific function. It is a part of a larger system which may not be a “computer”Works in a reactive & time constrained environment.

Any electronic system that uses a CPU chip, but that is not a general-purpose workstation, desktop or laptop computer is known as embedded system. Such systems generally use microprocessors; microcontroller or they may use custom-designed chips or both. They are used in automobiles, planes, trains, space vehicles, machine tools, cameras, consumer and office appliances, cell phones, PDAs and other handhelds as well as robots and toys. The uses are endless, and billions of microprocessors are shipper every year for a myriad of applications.

In embedded systems, the software is permanently set into a read-only memory such as a ROM or flash memory chip, in contrast to a general-purpose computer that loads its programs into RAM each time. Sometimes, single board and rack mounted general-purpose computers are called "embedded computers" if used to cont

Embedded System Applications :-

• Consumer electronics, e.g., cameras, cell phones etc.
• Consumer products, e.g. washers, microwave ovens etc.
• Automobiles (anti-lock braking, engine control etc.)
• Industrial process controller & defense applications.
• Computer/Communication products, e.g. printers, FAX machines etc.
• Medical Equipments.
• ATMs
• Aircrafts

There are two types of Microcontroller architecture designed for embedded system development. These are:

1. RISC- Reduced instruction set computer :  RICS stands for Reduced Instruction Set Computer. The philosophy behind it is that almost no one uses complex assembly language instructions as used by CISC, and people mostly use compilers which never use complex instructions. Therefore fewer, simpler and faster instructions would be better, than the large, complex and slower CISC instructions. However, more instructions are needed to accomplish a task. Atmell’s AVR microcontroller based on RISC architecture. 
2. CISC- Complex instruction set computer : CISC stands for Complex Instruction Set Computer. Most PC's use CPU based on this architecture. For instance Intel and AMD CPU's are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instructions. MCS-51 family microcontrollers based on CISC architecture. 

 DIFFERENCE BETWEEN MICROPROCESSORS AND MICROCONTROLLERS:

• A Microprocessor is a general purpose digital computer central processing unit(C.P.U) popularly known as CPU on the chip. The Microprocessors contain no RAM, no ROM, and no I/P O/P ports on the chip itself. On the other hand a Microcontroller has a C.P.U(microprocessor) in addition to a fixed amount of RAM, ROM, I/O ports and a timer all on a single chip.
• In order to make a Microprocessor functional we must add RAM, ROM, I/O Ports and timers externally to them,i.e any amount of external memory can be added to it. But in controllers there is a fixed amount of memory which makes them ideal for many applications.
• The Microprocessors have many operational codes(opcodes) for moving data from external memory to the C.P.U  whereas Microcontrollers may have one or two operational codes.