The Intel 80487 (i487SX) is basically a normal 486DX CPU which can detect and disables the primary 486SX CPU. All the processing will be done by the i487.

Cyrix reverse engineered the 386 and made their own version. They used their 386 as base for the 486 and made it compatible with 386 motherboards. This allowed users to upgrade to faster CPU's without overhauling the whole PC. Companies like IIT made 487-compatible co-processors for the "386-based 486's".