RPC-1 and RPC-2 are designations applied to firmware

Firmware

In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...

 for DVD drives. Older DVD drives use RPC-1 firmware, which allows DVDs from any region to play. Newer drives use RPC-2 firmware, which enforces DVD region coding

DVD region code

DVD region codes are a digital-rights management technique designed to allow film distributors to control aspects of a release, including content, release date, and price, according to the region...

 at the hardware

Hardware

Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....

 level. See DVD region code#Computer DVD drives for further information.

Newer RPC-2 drives can be converted to RPC-1 with the same features as before by using alternative firmware on the drive. Most drives are OEM Lite-On drives and require use of LtnRPC for multi-region and LtnFW to deal with firmware.