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Discussion in 'iMac' started by paalitha, May 10, 2018.
Is it possible to use a 2009 late imac 21.5 as a monitor for a new mac air?
The Late 2009 21.5" iMac doesn't support Target Display Mode.
Yes, the iMac late 2009 supports Target Display Mode
Cable Supported: Mini DisplayPort to Mini DisplayPort
Port on Source Computer: Mini DisplayPort or Thunderbolt
Thunderbolt ports are backwards compatible, meaning they support MiniDisplay Port cables. Your iMac 2009 with MiniDisplay Port does not support Thunderbolt. So you will need a Mini DisplayPort to Mini DisplayPort cable; this would then be plugged into Mini DisplayPort in 2009 iMac and Thunderbolt port in the Air.
That information is incorrect. The OP asked about a Late 2009 21.5-inch iMac. Only the 27-inch from that era supports Target Display mode (TDM). The 21.5-inch iMac did not support TDM until 2011, when the iMac included thunderbolt.