Windows tests the short block read/write speed of the readyboost drive. If it is not fast enough(faster than a hard drive), it will not use it. You would be much better off using the $100 or so spent on the SD card for a 32gb SSD; It will hold the OS(about 13gb) and then some. Readyboost is not a substitute for ram. It is only for small blocks that can be read faster than on a hard drive. You are also limited to a maximum of 4gb.