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Continue to ChatiMac EFI Firmware update 1.4 (Radeon HD 4850) https://www.appletips.nl/imac-efi-firmware-update-14-radeon-hd-4850/
iMac EFI Firmware update 1.4 (Radeon HD 4850) https://www.appletips.nl/imac-efi-firmware-update-14-radeon-hd-4850/