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The absence of serial ports, SCSI port, IRTalk, floppy drive, internal microphone, and stereo speakers, and the addition of the USB port, 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.
The iBook 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 iBook has no ADB ports. The ADB Manager, however, will still be present to retain compatibility with programs that require it.
The system software in the iBook has an ADB shim layer to allow USB keyboards and mice to appear as legacy ADB devices. The PMU99 provides the interfaces to the keyboard and mouse and communicates with the system by simulating ADB packets that are interpreted by the ADB Manager.
For external USB mice and keyboards to be fully compatible and interoperate seamlessly with the built-in keyboard and trackpad, an ADB shim is used to convert USB mouse and keyboard events into ADB packets.
Note
The built-in trackpad and keyboard also appear to the system as ADB devices, as described in the section Power Controller IC.
Although there is no SCSI connector on the iBook, the high-level SCSI interfaces will remain in the system. That allows for possible future 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.