The 486s are very similar to their immediate predecessor, the Intel 80386DX. The main differences are that the 486 has an optimised instruction set, has an on-chip unified instruction and data cache, an optional on-chip floating-point unit (FPU), and an enhanced bus interface unit. These improvements yield a rough doubling in performance over an Intel 80386 at the same clock rate.
There are several suffixes and variants including:
Intel 486DX - 486SX with a working FPU.
486SX-2 - runs at twice the external clock rate.
486SL - 486DX with power conservation circuitry.
OverDrive - 486DX-2 with a slightly different pinout for use in 486SX systems.
RapidCAD - 486DX in a special package with a companion FPU dummy package for use in Intel 80386 systems.
The 486 processor has been licensed or reverse engineered by other companies such as IBM, AMD, Cyrix, and Chips & Technologies. Some are almost exact duplicates in specications and performance, some aren't.