Apple has released an update for early-generation 1.8GHz Power Mac G5s.

The update is uniquely for the 1.8 GHz, (600 MHz bus), single-processor Power Mac G5, which shipped in late 2004. It improves the reliability of the machine, especially after it has been inactive for “two hours”, Apple said.

The software aims to resolve a number of known issues affecting these Macs, including unexpected freezes when playing some games or QuickTime movies; a non-responding optical drive when the computer has been unused for “about two hours”; problems with Internet Connect; and a failure to wake attached displays.

The company has issued specific instructions for the installation of the software, recommending users save their work and quit any open applications.

Apple warns: “Once the update begins, do not cancel or interrupt it. The update takes over one minute to complete. During the update, the Power Mac fans run at full speed. They return to normal once the update is complete.”

It requires Mac OS X 10.4.3 or later to be installed on the Power Mac. The 1MB update is available through Software Update.