AMD's version of the 386SX. It's not much different compared to the 386DX from both AMD and Intel. The SX versions are 32 bits internally but have a 16 bit external bus for communication with memory, chipset and such.

I probably mentioned it elsewhere but: don't confuse the SX/DX from a 386 with the SX/DX from a 486. They don't mean the same. Both the 386SX and 386DX don't have a FPU (co-processor). The 486SX and 486DX both have a 32 bit external bus but the SX doesn't have a co-processor. The 486DX is 'full-blown' and has a co-processor built-in.