they reversed engineered the Playstation BIOS, and wrote their own code to emulate the BIOS so the Virtual Game Station and Bleem didn't need the PSX ROM. But Sony and their army of lawyers fought and won, then gained ownership of the PSX emulators and then took them off the market. A pity because Bleem ran the PSX games on a modern PC that worked better than a real Playstation because they could tweak the resolution to whatever the videocard could handle. Also no "Choppy" sound in Bleem like the real PSX and PSOne had for some of the movies.
If someone were to reverse engineer the Apple PowerMac BIOS APIs or OSX APIs, then Apple would sue them.
In the old days, Compaq and company reversed engineered IBM's BIOS and then wrote their own version of it sans the BASIC language part.