In 1971, INTEL Corporation released the world’s first microprocessor, named the INTEL 4004, a 4-bit microprocessor. It addresses 4096 memory locations of word size 4-bit. The instruction set consists of 45 different instructions. It is a monolithic IC employing large-scale integration in PMOS Technology. The INTEL 4004 was soon followed by a variety of microprocessors, with most of the major semiconductor manufacturers producing one or more types.
1. First Generation Microprocessors: The microprocessors introduced between 1971 and 1973 was the first generation processors. They were designed using PMOS technology. This technology provided low cost, slow speed, and low output currents and was not compatible with TTL (Transistor-Transistor Logic) levels.
The first-generation processors require a lot of additional support from ICs to form a system. They may require as high as 30 ICs to form a system. The 4-bit processors are provided with only 16 pins, but 8-bit and 16-bit processors are provided with 40 pins. Due to the limitations of pins, the signals are multiplexed.
2. Second Generation Microprocessors: The second-generation microprocessors appeared in 1973 and were manufactured in NMOS Technology. The NMOS technology offers faster speed and higher density than PMOS
and it is TTL compatible.
3. Third Generation Microprocessors: After 1978, the third generation microprocessors were introduced. These are 16-bit processors and designed using HMOS (High-density MOS) Technology.
4. Fourth Generation Microprocessors: The fourth-generation microprocessors were introduced in the year 1980. The fourth-generation processors are 32-bit processors and are fabricated using the low-power version of the HMOS technology called the HCMOS. These 32-bit microprocessors have increased sophistication that competes strongly with the mainframes.
5. Fifth Generation Microprocessors: In microprocessor technology, INTEL has taken a leading edge and is developing more and more new processors. The INTEL Pentium processor released in the year 1993 is considered a fifth-generation processor. The Pentium is a 32-bit processor with a 64-bit data bus and is available in a wide range of clock speeds from 60 MHz to 3.2 GHz. With the improvement in semiconductor technology, the processing speed of microprocessors has increased tremendously. The 8085 released in the year 1976 executes 0.5 Million Instructions Per Second (0.5 MIPS).