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27-inch iMac Graphics Firmware Update 1.0 is available via Software Update or for download direct from Apple. The small 683KB file requires Mac OS X 10.6.2 or later.
Apple said the firmware update applies to the big-screen iMac's ATI Radeon HD 4670 and 4850 graphics cards. It reportedly addresses issues that may cause image interruption or display flickering.
Users are asked not to shut off the power on their iMac during the update. Loss of power could result in the iMac failing to start.
Earlier this month, as reports of flickering on the 27-inch model continued to grow, shipments of the hardware were delayed past Christmas for some customers. Apple responded by apologizing for the delay, which the company implied was due to high demand. However, Apple did not state whether the display issues played a role.
"The new iMac has been a huge hit and we are working hard to fulfill orders as quickly as possible," a company official said. "We apologize for any inconvenience or delay in delivery this may cause our customers."
An example of the screen distortion issue is included below:
Despite the reports of issues, the iMac was the best-selling desktop in the U.S. in the month of October. The new 21.5-inch model took the top spot, while the big-screen 27-inch version came in at No. 3 for the month.