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The SCSI expert is supplied by Apple in the firmware of PCI-based Power Macintosh computers. For a discussion of experts, see Terminology.
The SCSI expert is simpler than some other experts and places fewer demands on Open Firmware and the native driver model. A PCI card that wants to register a SIM with the SCSI Manager must place information in the device tree that includes its name and reg properties. To be recognized by SCSI Manager 4.3 as a SCSI device, the device must have a device_type property of 'scsi'. This is important because it is the primary identifier that causes the SCSI expert to load the SIM. The device_type property is generated by the Mac OS startup code and is based on the PCI configuration space parameter class-code, which must have a value of "mass storage" (01). With the DriverOSService.service[x].serviceCategory value of "blok", the device_type property completely identifies the SIM code to the SCSI expert.