Apple has updated its CD-ROM drive firmware for the iMac to improve its performance.

According to the notes on Apple’s Web site, the CD firmware update reduces disc vibration, caused by unbalanced CDs spinning at higher speeds in the internal CD-ROM drive. The vibration may cause the drive to have difficulty reading the CD.

The update also corrects intermittent delay on some iMac models that occurs when there's no CD in the CD-ROM drive.

The update replaces iMac CD Firmware Update 1.0, and is supported by Mac OS 8.1, 8.5x and 8.6.