SCSI interface. AppleCD 600i CD-ROM Drive, internal, tray load, Apple CD Drive. Apple 678-0065. Drive may be either Matsushita Model CR-504-L or Sony Model CDU-75S-25.
Mounting carrier or sled not included, but available here.
Note that the Matsushita CR-504-L drives currently in stock are not Apple branded and may not contain the firmware needed to actually boot from the drive. Workarounds are possible. Drivers can be found at the Mac Driver Museum.