PAT requires higher quality memory. SOme chips will work with it, others won't, even from the same model of chip. One way to have a better chance to get it to work is to go up one step in speed. IE, if yo'ure not overclocking, typical ram you'd want would be PC3200. So if you wanted to use PAT, would have a better chance of it working if you used PC4000 ram, even though you were running it at PC3200 speeds.