Drivechip
Not to be confused with Drive Replacement Chip.
Although the Gamecube DVD drive can read backups using the debug commands (and uploading patch code) YAGCD Section 5.7.2, there was a debug communications port 'CN302' which certain people found out could also be used for a similar patch upload.
Drivechips
Two modchips exist which are Drivechips: