In the commons language the architecture means structural design of a building. Similarly by microprocessor architecture in a broad sense we mean the structural design of the digital circuit responsible for computing. The digital circuit of the microprocessor is designed in such a way that if a proper binary input called instruction) is given to this circuit we get the desired output. To understand this we can see the behaviour of a two input AND gate in which we get 1 as an output if and only if both the input are 1 similarly an adder circuit gives the output which is the addition of two input bits. Hence we can imagine that how complicated is the design of the digital circuit of an microprocessor which can give the output according to various instruction given to it like add subtract move and or exclusive or etc. This can be achieved in different manner. That means there may be many possible digital circuits to achieve in different manner. That means there may be many possible digital circuits to achieve the same output. Therefore the architecture of two different microprocessors might be different. The way they ad two numbers may be quit similar but a complicated task like finding out the tangent of an angle will be performed in a different way in two different microprocessors. One microprocessor may perform it very easily while the other may with difficulty.
Various features which affects the architecture of a microprocessor are:
a.Length of data word which is decided by the size of the data bus.
b.The size of memory accessed by the microprocessor which is decided by the size of the address bus.
c.The speed of execution of instruction which id seceded by the clock frequency at which microprocessor can operate.
d.The type of registers.
e.The types of instructions.
f.The types of addressing modes.
g.Various supporting hardware which are compatible with that microprocessor.
These are various features which make are microprocessor different from other microprocessor. We will discuss these features in detail in different parts of this book especially for 8085 microprocessor. Various advanced processors are discussed in chapter 11.