Apple has released another patch meant to fix lock-up problems with its iMacs, the second in a week.

iMac Software Update 1.2.1 (Tiger) is intended for 20-inch and 24-inch aluminium-clad iMacs operating on 2.0, 2.4 and 2.8GHz running Mac OS X v10.4 "Tiger." The update is available for download from Apple's website.

Recently, Apple acknowledged a problem that can cause these models of iMac to freeze suddenly under certain circumstances. Last week, the company offered software updates for Leopard and Tiger users affected by the issue.

This update "improves the performance and reliability of graphics-intensive games and applications and fixes an issue that some customers encountered when installing Mac OS X Leopard after applying iMac Software Update 1.2," according to Apple.