Starting with its third generation of CPU, Intel began to diversify it product. Intel manufactured the 386 and 486 CPUs in an SX and DX version. What's the difference? That depends which generation you are talking about.

In the 386, the SX has a 16 MB maximum addressable memory, and a 16-bit data bus width. The DX has 4 GB maximum addressable memory, and a 32-bit data bus width.

The 486SX does not have an internal math coprocessor. The 486DX does have an internal math coprocessor.