The microprocessor age began with the advancement in IC technology to put all necessary functions of a CPU into a single chip.

First generation microprocessor:

Intel started marketing its first microprocessor in the name of Intel 4004 in 1971. This was an a4-bit microprocessor having 16-pins in a single chip of PMOS technology. This was called the first generation microprocessor. The Intel 4004 along with a few other devices was used for making calculators. The 4004 instruction set contained only 45 instructions. Later in 1971, INTEL Corporation released the 8008 – an extended 8-bit version of the 4004 microprocessor. The 8008 addressed an expanded memory size (16KB) and 48 instructions.

Limitations of first-generation microprocessors are small memory size, slow speed and instruction set limited its usefulness.

Second-generation microprocessors:

The second generation microprocessor using NMOS technology appeared in the market in the year 1973. The Intel 8080, an 8-bit microprocessor, of NMOS technology was developed in the year 1974 and required only two additional devices to design a functional CPU. The advantages of second-generation microprocessors were

  • Large chip size (170x200 mil) with 40-pins. 
  • More chips on decoding circuits.
  • Ability to address large memory space (64-K Byte) and I/O ports(256).
  • More powerful instruction sets. 
  • Dissipate less power.
  • Better interrupt handling facilities.
  • Cycle time reduced to half (1.3 to 9 m sec.)
  • Sized 70x200 mil) with 40-pins.
  • Fewer Support Chips Required
  • Used Single Power
  • Supply Faster Operation

The 8080 microprocessor addresses more memory and execexecutesitional instructions but executes them 10 times faster than 8008. The  8080 has memo ry of 64 KB whereas for 8008 16 KB only. In 1977, INTEL, introduced 8085 which was an updated version of 8080 last 8-bit processor.

The main advantages of 8085 were its internal clock generator, internal system controller, and, higher clock frequency.

Third Generation Microprocessor:

In 1978, INTEL released the 8086 microprocessor, and ar later it released the 8088the. Both devices were 16 b16-microprocessors, which executed instructions in less than 400ns. The  8086 and 8088 and address of memory and rich instruction set to 246.16-bit processors were designed using HMOS technology. The Intel 80186 and 80188 were the improved versions of Intel 8086 and8088, respectively. In addition to 16-ba it CPU, the 80186 and 80188 had programmable peripheral devices integrated into Tinto same package.

Fourth Generation Microprocessor:

The single chip 32-bit microprocessor was introduced in the year 1981 by Intel as iAPX 432. The other 4thgeneration microprocessors were; Bell Single Chip Bellmac-32, Hewlett-Packard, National NSl NSW2, Texa s Instrument99000. Motorola 68020 and 68030. The l in the year 1985 announced the 32-bit microprocessor(80386). The 80486 has already been announced and is also a 32-bit microprocessor.

The 80486 is a combination 386 processor a math coprocessor, and a cache memory controller on a single chip.

The Pentium is a 64-bit superscalar processor. It can execute more than one instruction at a time and has a full 64-bit data bus and 32-bit address bus. Its performance is double thanthat8of 6.

Features of 8086

  • It is a 16-bit μp.
  • 8086 has a 20-bit address bus that can access up to 2^20 memory locations (1 MB).
  • It can support up to 64K I/O ports. •It provides 14, 16 -bit registers.
  • It has multiplexed address and data bus AD0- AD15 and A16 – A19.
  • It requires a single phase clock  with a 33% duty cycle to provide internal timing
  • 8086 is designed to operate in two modes, Minimum and Maximum.
  • It can pre-fetches up to 6 instruction bytes from memory and question to speed up instruction execution.
  • It requires +5V a power supply. •A 40 p40-pinl in lin-linekage.