What is the difference between the 386DX and the 386SX?

The main difference between the two is that the 386SX had a 16-bit data bus, while the 386DX had a full 32-bit data bus. This meant that it took twice as many cycles to transfer data across the bus, and limited the 386SX to a maximum of 16 MB of RAM, although it could still technically page up to 4 GB.