We can categorize the microprocessor according to the generations or according to the size of the microprocessor:
First Generation (4 - bit Microprocessors)
The first generation microprocessors were introduced in the year 1971-1972 by Intel Corporation. It was named Intel 4004 since it was a 4-bit processor.
It was a processor on a single chip. It could perform simple arithmetic and logical operations such as addition, subtraction, Boolean OR and Boolean AND.
I had a control unit capable of performing control functions like fetching an instruction from storage memory, decoding it, and then generating control pulses to execute it.
Second Generation (8 - bit Microprocessor)
The second generation microprocessors were introduced in 1973 again by Intel. It was a first 8 - bit microprocessor which could perform arithmetic and logic operations on 8-bit words. It was Intel 8008, and another improved version was Intel 8088.
Third Generation (16 - bit Microprocessor)
The third generation microprocessors, introduced in 1978 were represented by Intel's 8086, Zilog Z800 and 80286, which were 16 - bit processors with a performance like minicomputers.
Fourth Generation (32 - bit Microprocessors)
Several different companies introduced the 32-bit microprocessors, but the most popular one is the Intel 80386.
Fifth Generation (64 - bit Microprocessors)
From 1995 to now we are in the fifth generation. After 80856, Intel came out with a new processor namely Pentium processor followed by Pentium Pro CPU, which allows multiple CPUs in a single system to achieve multiprocessing.
Other improved 64-bit processors are Celeron, Dual, Quad, Octa Core processors.