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The upcoming high performance desktop machines are demanding additional storage peripheral support beyond hard disk drives. Specifically, CD-ROM and tape drives will demonstrate rapid unit growth rates as these peripherals become a more standard part of the desktop's configuration. Today's CD- ROMs and tape drives have multiple interfaces that present compatibility and performance issues. Development of a standard IDE interface for both CD-ROMs and tape drives solves cost, compatibility, performance, and ease-of-use issues in conjunction with enabling the attachment of non- disk devices via the IDE interface.
Western Digital, with its AT interface expertise, has taken the leadership position in expanding the IDE interface to support non-disk peripherals by authoring the AT Attachment Packet Interface (ATAPI). The specification defines a standard method for interfacing to a CD-ROM drive (and other non-disk devices) utilizing the existing ATA host computer hardware and cabling. ATAPI supplements the definitions of an ATA mass storage peripheral found in the ATA specification and is compatible with existing ATA hardware without any changes or additional pins.
Traditional computer architecture has used a register based transport mechanism. Modern architectures now use packet-based transport mechanisms. ATAPI is an enhancement to IDE that follows this trend. Benefits of including a packet-based scheme means adding very few IDE operation codes. The ATAPI specification adds only a single new IDE command to obtain functionality and only two additional new IDE commands to address compatibility. Once a packet-based interface was defined, the next issue was deciding what command packets definitions to utilize. Given widespread support for SCSI within peripherals and within existing operating systems, it was decided to derive ATAPI command packets from SCSI to minimize development time and expense.
The ATAPI specification is being reviewed by an industry working group that consists of market-making system manufacturers, CD-ROM suppliers, silicon designers, BIOS developers, and Western Digital. The objective is to finalize the ATAPI specification around which these companies will design and manufacture products for the personal computer industry. Although the exact strategy has yet to be decided upon, the document will eventually be submitted to a standards committee for adoption. Putting it All Together
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