In the iMac, the Pangea IC provides an Ultra ATA channel that is connected to the internal hard disk drive and the optical drive. The Pangea IC provides DB-DMA (descriptor-based direct memory access) support for the Ultra DMA interface.
The internal hard disk drive is connected as device 0 (master) in an ATA Device 0/1 configuration; the optical drive is connected as device 1 (slave). The internal hard disk drive uses the ATA5 protocol and the CD-RW drive uses the ATA4 prototcol.