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The absence of serial ports, ADB ports, a SCSI port, and a floppy drive, and the addition of the USB and FireWire ports, may affect the behavior and appearance of various system components. Modifications for such changes are in Mac OS 9 itself.
Some managers and drivers remain in the system to support existing applications that depend on those older devices. New applications are expected to use the new I/O channels such as USB and FireWire.
The PowerBook computer has no built-in floppy disk drive, so the existing .Sony driver has been disabled using the same techniques as in the iMac software. MFM Floppy disks can be supported by a USB-based LS-120 disk drive developed by a third party.
The PowerBook computer has no ADB ports. The ADB Manager is still present, to retain compatibility with programs that require it.
The system software has an ADB shim layer to allow USB keyboards and mice to appear as legacy ADB devices.
Although there is no SCSI connector on the PowerBook computer, the high-level SCSI interfaces remain in the system. That allows for possible support for SCSI devices using a USB-to-SCSI adapter. Such an adapter would take the USB commands coming from the USB port and convert them into SCSI commands to send to the drive. A SCSI driver would also need to be written that would take the SCSI commands coming from the system and embed them in USB commands that would be sent to the device through the adapter.