This is readyboost again? Wasn't that what it was called? Vista had a caching module in it for handling a side cache of flash on a stick. And I think you could 'pin' certain read-only files (practically this would mean executables) so that it would use duplicate copies off the flash in preference to the masters on the HD and take them out of the boot process. It worked really well in certain special circumstances for speeding up the boot process as I remember but only if the flash was extremely fast, and most of it wasn't, so a lot of the time it didn't do much at all. I certainly tried it but found it very difficult to get hold of sufficiently high quality sticks back then in the ancient times. The other problem was that optimising placement of files on the HD for boot fetch sequence friendliness removed a lot of the seek time and without that the sequential read rate of decent hard disks was a bit too good back then. It might have been better perhaps with laptops, as their hard disks used to be a bit less performance for various reasons and also flash was good for power saving too. There was even talk of hybrid drives and flash on boards, iirc.