Now that we have learnt the basics of Microprocessors, lets see the history of Microprocessors. The evolution of microprocessors has been divided into five generations namely first, second, third, fourth and fifth generations.

First Generation Microprocessors

  • First Generation Microprocessors were introduced in the year 1971-1973.
  • The instructions of these microprocessors were processed serially, they fetched the instruction, decoded and then executed it.
  • When an instruction of the microprocessor was finished, then the microprocessor updates the instruction pointer & fetched the following instruction, performing this consecutive operation for each instruction in turn.
  • INTEL created the first microprocessor 4004 that would run at a clock speed of 108 KHz. It had nearly 2300 transistors
    • 4-bit microprocessor
    • 4 KB main memory
    • 45 instructions
    • PMOS technology
    • 4004 was first programmable device which was used in calculators
  • During this period, the other microprocessors in the market including Rockwell international PPS-4, INTEL- 8008 and National semiconductors IMP-16 were in use.
  • Intel 8008
    • Year of introduction 1972
    • 8-bit version of 4004
    • 16 KB main memory
    • 48 instructions
    • PMOS technology
    • Slow

Second Generation Microprocessors

By the late 1970s, enough transistors were available on the IC to usher in the second generation of microprocessor sophistication: 16-bit arithmetic and pipelined instruction processing. This generation is defined by overlapped fetch, decode, and execute steps. As the first instruction is processed in the execution unit, the second instruction is decoded and the third instruction is fetched. The difference between the first generation microprocessor and second generation microprocessors was mainly the use of new semiconductor technologies to manufacture the chips. The result of this technology resulted in a fivefold increase in instruction, speed, execution and higher chip densities.
Intel 8080 and 8085 are some examples of second generation computers.

Intel 8080

  • This 8 bit microprocessor Consisted of 6000 Transistors.
  • Clock Speed was 2 MHz
  • Year of introduction 1973
  • 8-bit microprocessor
  • 64 KB main memory
  • 10X faster than 8008
  • NMOS technology
  • Drawback was that it needed three power supplies.
  • Small computers (Microcomputers) were designed in mid 1970’s using 8080 as CPU.

Intel 8085

  • Year of introduction 1975
  • 8-bit microprocessor-upgraded version of 8080
  • 64 KB main memory
  • 246 instructions
  • Intel sold 100 million copies of this 8-bit microprocessor  uses only one +5v power supply.
Some other examples of second generation microprocessors are Motorola 6800 and 6801, and Zilogs-Z80. Owing to their super fast speed, they were costly as they were based on NMOS technology fabrication.

Third Generation Microprocessors

The third generation, introduced in 1978, were 16-bit processors with minicomputer-like performance. This generation came about as IC transistor counts approached 250,000. The computers were designed using HMOS technology. INTEL 8086/80186/80286 were developed in this generation.

Intel 8086/8088

  • Year of introduction 1978 for 8086 and 1979 for 8088 
  • 16-bit microprocessors
  • Data bus width of 8086 is 16 bit and 8 bit for 8088
  • 1 MB main memory
  • 6 byte instruction cache for 8086 and 4 byte for 8088
  • Other improvements included more registers and additional instructions
  • In 1981 IBM decided to use 8088 in its personal computer

Intel 80286

  • Year of introduction 1983
  • 16-bit high performance microprocessor with memory management & protection
  • 16 MB main memory.
  • Instruction execution time is as little as 250 ns
  • Concentrates on the features needed to implement multitasking.
Some other examples of third generation microprocessors included Motorola 68000, 68010, 68020. The depth of the pipeline increased to five or more stages, that resulted in increase of speed upto five times. These types of microprocessors were different from the previous generations of microprocessors in that all main workstation industrialists began evolving their own ISC based microprocessor architectures.

Fourth Generation Microprocessors

As many industries converted from commercial microprocessors to in house designs, the fourth generation microprocessors entered a phase of outstanding design with a million transistors.

Intel 80386

  • Year of introduction 1986
  • Intel’s first practical 32-bit microprocessor
  • 4 GB main memory
  • Improvements include page handling in virtual environment
  • Includes hardware circuitry for memory management and memory assignment
  • Memory paging and enhanced I/O permissions Intel


  • Year of introduction 1989
  • 32-bit high performance microprocessor
  • 4 GB main memory
  • 8 K byte cache on one package

Fifth Generation Microprocessors

Fifth generation microprocessors employed decoupled super scalar processing, and their design soon exceeded 10 million transistors. In fifth generation, PCs were a low-margin, high volume business conquered by a single microprocessor.


  • Year – 1993
  • Transistors – 3,100,000
  • Data – 32 bits
  • Clock Speed – 60 Mhz

Pentium II

  • Year – 1997
  • Transistors – 7,500,000
  • Data – 64 bits
  • Clock Speed – 233 Mhz

Pentium III

  • Year – 1999
  • Transistor – 9,500,000
  • Data – 64 bits
  • Clock Speed – 450 Mhz

Pentium IV

  • Year 2000
  • Transistors – 42,000,000
  • Data – 64 bits
  • Clock Speed – 1.5 GHz

Lets learn about Intel 8085 now, here.