I had same issue with the eSATA external port on my Asus Rampage II Genie motherboard running dual O/S (Win XP 32 and Win 7 64). This board is very similar to the Asus P6T. An external drive on the eSATA would come and go, as to being visible and accessible under Explorer, with no apparent pattern. The issue occurred with both O/S. The above driver was a later version than what Asus had on their web site for the JMicron controller, and when installed under each O/S, it fixed the problem on both. The ACHI mode (under advanced configuration settings in the BIOS setup) makes this eSATA drive hot pluggable. This was a great fix - thanks.