Can two imacs read and write simultaneously to one thunderbolt duo drive

WD External Drives External Drives for Mac
2

No, you can not mount the disk drive in two separate computer systems at the same time through a direct connection.

The second Thunderbolt connector works under the same principle as Firewire for daisy-chaining: Additional devices are connected together to the second port and they operate through the main device connected directly to a computer system. 

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