In Windows Vista there is a new feature called ReadyBoost that lets you insert a flash drive or a memory card into the system then Windows will store the commonly used files for quicker access than turning off the hard drive. Mean it will create a Cache file to store the temporary files in the flash drive for serve you to open it again.
Turning this feature on is simple. Just put the flash drive, SD card, or whatever flash device you want into your computer. You’ll see this dialog pop up:
Click the “Speed up my system” link, and you’ll be taken to the ReadyBoost panel for the flash drive:
Just select Use this device, and set the amount of space you want to use. Windows will create what is essentially a paging file on the disk, and will use it for faster access.
You will see a cache file in ur flash drive as below: