A Mac OS 9.1 CD is required to install Mac OS 9.1 on original Power Macintosh computers.
Affected computers
Power Macintosh 6100 series
Power Macintosh 7100 series
Power Macintosh 8100 series
Power Macintosh 8115
Workgroup Server 6150
Workgroup Server 8150
Workgroup Server 9150
After placing the Mac OS 9.1 CD in the drive, restart the computer. Press and hold the "c" key during system startup time. When the computer is started up from CD, you will see a unique CD desktop pattern as confirmation.
The downloadable Mac OS 9.1 update available from
Apple Downloads is not compatible with original (NuBus-based) Power Macintosh computers.