The initial 80386 was a 32-bit chip, incorporated 275,000 transistor, was capable of performing more than five million instructions every second (MIPS), sold for $299, and was available in clock speeds between 12 and 40MHz.
The Intel 80386SX processor was introduced in 1988 as a low cost alternative to the original 386 processor. The 80386SX lacked a math coprocessor but still featured the 32-bit architecture and built-in multitasking. The chip was available in clock speeds of 16MHz, 20MHz, 25MHz, and 33MHz.
The 80386DX or 386DX processor was the original 386 processor renamed and not a different 386 processor.
Finally, the 80387 was the math coprocessor used with the Intel 386 processor.
Some 386DX 16MHz Intel processors had a small bug, which appeared as a software problem. The bug occurred when running true 32-bit code in a program such as within OS/2 2.x, Unix/386, or Windows in Enhanced mode. The bug would cause the system to lock up and is a difficult issue to determine without having Intel look at the chip. Chips that passed the test, and all subsequent chips that were bug-free, were marked with a double-sigma symbol. 386DX chips that are not marked with either of these symbols may have not been tested by Intel and may be defective.