You can use any drive that is faster than 2.5MB/s for 4KB random reads, and it needs a seek time of less than 1ms. See http://windowshelp.microsoft.com/Windows/en-US/Help/12428141-2e4c-43ab-8dd2-a6ed6e3b87761033.mspx or http://en.wikipedia.org/wiki/ReadyBoost. :)