In the mid-90s, arcade piracy was rampant. To combat bootleggers, Capcom engineered a "kill switch" into the CPS2 hardware.
The CPS2 was region-locked by color (Blue/Green for Western markets, Gray/Orange for Asia). In some ROM sets, the "parent" game file acts as a functional base for all regional "child" versions, which can lead to confusion about needing a system-wide BIOS. cps 2 bios