The microprocessor is a small computer or CPU (central processing unit) used to do arithmetic and logical operation, controlling the system and storing the data etc. the microprocessor will process the data of the input/output peripherals and give the results back to them to function. The first commercial Microprocessor was released by Intel in year 1971 November named as 4004. It is 4-bit microprocessor. But first microprocessor was development by Garrett Research’s in the year 1968. Block diagram of microcontroller shown below:

The initial Microprocessor uses the Von-Neumann architecture. In the Von Neumann architecture the data memory and program memory are placed in one memory. If processor wants to process an instruction from memory or request from the I/O, it has to get instruction through a bus from the memory or I/O, Place it in the registers and process it in the registers. Processor can save the result in the memory through the bus. But this architecture has some drawbacks like it is slow and data operations cannot occur at the same time because they share the same common bus. Later Harvard architecture is developed. In the Harvard architecture the data memory and program memory are placed as separate memory and separate buses are connected to communicate each other. There are also two types of CPU micro programming and hardwired programming. Microprogramming is slow when compared to hardwired. Hardwired implementation is mainly of logic gates and passive elements. Microcode is used to in the microprogramming..

The instruction set architecture (ISA) also plays an important role in the microprocessors. There are different instructions set architecture microprocessors available in them market. They are

1. Complex programming Instruction Set Computer: this was first ISA. In the complex instruction set computer (CISC) instruction set is complex instructions which will take long time to execute; complex instruction may consist of opcode addressing mode operand etc. The execution speed will be slow. X86 architecture is example

2. Reduced Instruction Set Computer: in the reduced instruction set computer (RISC) the instruction set will be small and execution speed will be fast. The implementation is simple and does not require complex architecture. RISC is widely used in embedded applications. SHARC and POWERPC use RISC.

There are other architecture like Very Long Instruction word (VLIW) and FUSION of RISC AND CISC architecture etc.

Microprocessor should be chosen according to the application for small application you don’t need CISC. You cannot use RISC for large application. According to the application and peripherals you are using microprocessor should be taken.