The third generation of x86 family, the Intel 80386 (i386) was a complete 32-bit processor with ability to address 4 GB of physical memory. The processor included new protected mode, that allowed the processor to fully utilize new 32-bit architecture and new features, like memory protection, paging, etc. Another new mode - virtual mode - could be used to run old 8086 applications without switching the processor back from protected mode to real mode. There were a few variations of the Intel 80386:
80386DX has 32-bit external data and address busses.
Low cost 80386SX had 16 bit external data bus and 24-bit external address bus. This processor supported only 16 MB of physical memory.
Low-power 80386SL with power management features, with 16-bit external data bus and 24-bit external address bus.
Embedded 80376 and 80386EX processors.
The Intel 80386 was produced at speeds up to 33 MHz, AMD produced even faster 40 MHz version.
IBM, CHIPS, AMD, Cyrix, MC, and TI all made their own versions of the 386.
This version has the bug fixed that originally kept 32-bit mode from working right. It is known as a Double Sigma version.