One of intel's intel 486 family of microprocessors (one of the last before the pentium). The 486DX has a working built-in floating point unit (FPU). The intel 486sx is effectively a DX with the FPU disabled. The DX has a pin to select the external data bus width (16 or 32).

The intel 487sx is a 486DX with a 486SX pinout.