The 387 SX is an add-on math co-processor that helps the computer conduct complex mathematics much more quickly. This chip is designed for use in conjunction with the 386SX processor (CPU).

Computers with the 386DX (which seems to be less common) cannot use 387SX co-processors. According to the 2008 edition of "The Secret Guide to Computers", they should use the 387DX instead.

The Intel 387 offers a good way to obtain faster performance from a 386 computer in certain types of applications. Make sure your PC allows such chips to be installed before you buy one.