TECHNICAL INFORMATION BULLETIN TIB Number 910805.1 05 August 1991 TITLE Hard Disk Device Driver Problems with Rewritable Optical PURPOSE Describes the problems in using a standard SCSI hard disk device driver or SCSI adapter ROM BIOS to communicate with Rewritable Optical drives. PROBLEMS AND QUESTIONS If you have any questions regarding any Technical Information Bulletin, contact the following: Micro Design International, Inc. 6985 University Boulevard Winter Park, FL 32792 Attention: Technical Support Phone: 407-677-8333 Fax: 407-677-0221 When using Rewritable Optical it is very important that you are using a device driver specifically written to support Rewritable Optical. There are many problems in using a standard SCSI hard disk device driver or a SCSI Adapter ROM BIOS to access Rewritable Optical. CURRENT PROBLEMS In response to a SCSI INQUIRY command, most Rewritable Optical drives identify themselves as direct-access storage devices (e.g., magnetic disk). Therefore, you may think that a standard SCSI hard disk driver or a SCSI adapter ROM BIOS can support Rewritable Optical. If you try, it may even "appear" to work fine, but the following problems exist in using a standard SCSI hard disk driver or SCSI adapter ROM BIOS to communicate with a Rewritable Optical drive: * Proper drive initialization. * Support of 1024 byte sector media. * Support of changing media. * ISO Standard media formatting. Some Rewritable Optical drives require the driver to send certain initialization commands to the drive on power up or after a bus reset. For example, an important error recovery procedure for the SONY Rewritable Optical drive is automatic write reallocation (AWR) of defective sectors. When the SONY drive detects a medium error during a write, erase, or verify operation of a write command, the sector is automatically reallocated and the data written to a spare sector. This reallocation process is completely transparent to the operating system. It must be enabled through a MODE SELECT command to the drive at power up or after a bus reset. A generic SCSI hard disk driver or SCSI adapter ROM BIOS would not perform this initialization and would receive medium errors back from the drive. This is the biggest danger in using a generic SCSI hard disk driver or SCSI adapter ROM BIOS to communicate with a Rewritable Optical drive. Another problem with using a hard disk driver is support for 1024 byte sector media. Rewritable Optical media currently is available in two physical sector sizes, 512 byte and 1024 byte sector media. Since most hard disk drives use 512 byte sectors, most hard disk drivers are limited to supporting only 512 byte sector media. The 1024 byte sector media has the advantage of greater capacity, and requires special driver considerations to support it. One of the important advantages of Rewritable Optical is removable media since it offers unlimited capacity by changing cartridges. This feature of removability can cause problems with existing hard disk drivers and adapter ROM BIOSs since they are written for fixed media SCSI hard disks. Most hard disk drivers do not expect the media to change or even become not ready. Even though handling of removable media is also dependent on which operating system you are using, a Rewritable Optical driver will support it. To support different defect management schemes, some Rewritable Optical drives require a mode specification when formatting the media. Only one of the format modes is compatible with the ISO standard defect management scheme. Even if your operating system supports formatting SCSI hard drives, it will not have the necessary code to select the ISO compatible format mode. This mode requires a format utility specifically written for Rewritable Optical. FUTURE PROBLEMS There are new Rewritable Optical drives on the market that supports both Rewritable Optical media and WORM media. These new drives are called Multifunction Optical drives. For approximately the same price of a Rewritable Optical you can get a Multifunction Optical which has the advantages of both Rewritable Optical and WORM in a single drive. A standard SCSI hard disk device driver or SCSI Adapter ROM BIOS will not be able to support the full functionality of this drive. This type of drive needs a device driver specifically written to support Multifunction Optical which supports both types of media, Rewritable and WORM. SUMMARY A driver specifically written for Rewritable Optical solves the most common problems you encounter when using a SCSI hard disk driver or SCSI adapter ROM BIOS to support Rewritable Optical. Besides solving these problems, a Rewritable Optical driver can offer many additional features to increase performance and expand flexibility.