imac as monitor?

[paalitha]

Is it possible to use a 2009 late imac 21.5 as a monitor for a new mac air?

 

[redheeler]

The Late 2009 21.5" iMac doesn't support Target Display Mode.

 

[Guy Clark]

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.

 

[DeltaMac]

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.