Fourth  Generation Microprocessor :

The single chip 32-bit microprocessor was introduced in 1981 by Intel as iAPX 432. The other 4th generation  microprocessors  were;  Hewlett-Packard, Bell  Single  Chip  Bellmac-32  , Texas Instrument99000, National  NSl  6032, Motorola 68030 and 68020.

The  power  of  the  microprocessor  went  on  increasing  with  the  advancement  in  the  integrated  circuit technology.  The VLSI technology culminated in the extremely complex microprocessor with as many as one billion transistors on a single chip. The Intel in the year 1985 announced the 32-bit microprocessor (80386). The 80486 has already been announced and is also a 32-bit microprocessor.

Mostly microprocessors were manufactured with HMOS (high density short channel MOS) technology because of the following benefits:

(i) Speed-power product was 4-times larger than NMOS. It's typical value was I-pico joule where as in the case of NMOS technology it was 4-pico joules.

(ii) Circuit density was roughly 2-times greater than NMOS. The typical NMOS density was 4128 um2 gate whereas it was 1852.5 um2 for HMOS