Several third-party developers have recently introduced iMac expansion cards. This has prompted questions about Apple's policy regarding the installation of cards into iMac, and if the use of these cards might void the customer warranty.
Apple will not provide repairs under warranty to iMacs that have been damaged due to the installation of any expansion card (including SDRAM and SGRAM cards), whether the card was installed by an authorized service technician or the customer.
Currently, the only cards that may be installed in iMac are SDRAM memory and SGRAM video memory cards in the iMac memory slots. Besides these two slots, there is an additional slot that was used by Apple during iMac development (often referred to as the mezzanine slot). This slot is for Apple use only. Apple has not published the specifications for this slot and is not recommending that any company develop products that rely on it.