A Microprocessor, popularly known as “computer on a chip” in its early days, is a general purpose central processing unit (CPU) fabricated on a single integrated circuit (IC) and is a complete digital computer (later microcontroller is considered to be more accurate form of complete computer). It is a small but very powerful electronic brain that operates at a blistering speed and is often used to carry out instructions of a computer program in order to perform arithmetic and logical operations, storing the data, system control, input / output operations etc. as per the instructions. The key term in the definition of a microprocessor is “general purpose”. It means that, with the help of a microprocessor, one can build a simple system or a large and complex machine around it with a few extra components as per the application. The main task of a microprocessor is to accept data as input from input devices then process this data according to the instructions and provide the result of these instructions as output through output devices. Microprocessor is an example of sequential logic device as it has memory internally and uses it to store instructions.
The internal structure of a microprocessor is shown below.
CISC architecture consists of full set of instructions that are complex, larger, have more computational power and so on. A single CISC instruction can be used to execute several low-level operations, multi-step operations and multiple addressing modes. The execution time of these instructions is long. Intel’s X86 is an example of CISC architecture.
RISC architecture was developed by realizing that instead of using full set of instructions, only the frequently used instructions are sufficient. In this architecture, the instructions are small and highly optimized. RISC processors are used where execution time of the instruction should be less and cost of development is less. The ARM devices are based on ARM architecture which is a subset of RISC.
The main reason for the development of microcontroller is to overcome the only drawback of the microprocessor. Even though microprocessors are powerful devices, they require external chips like RAM, ROM, Input / Output ports and other components in order to design a complete working system. This made it economically difficult to develop computerized consumer appliances on a large scale as the system cost is very high. Microcontrollers are the devices that actually fit the profile “Computer – on – a chip” as it consists of a main processing unit or processor along with some other components that are necessary to make it a complete computer. The components that are present on a typical microcontroller IC are CPU, memory, input / output ports and timers. The first microcontroller was developed in 1971 by Texas Instruments and is called TMS 1000. It was made available for commercial use in 1974.