If you have old USB key, SD card or SSD (Solid State Disk) which you do not use quite often, you can boost your computer's performance by simply plug in.
Windows 7 provides a feature called ReadBoost. It use flash (which is much faster than traditional hard disk) to cache the information to avoid read from hard disk. This can boost your computer's performance (like start application, start up, shut down) especially if your computer does not have much physical memory.
If your computer is already using SSD as boot disk, ReadBoost may not very useful.
Enable ReadBoost is simple, when plugin in a USB key or SD card (suppose your computer has SD card slot), a window will prompt you if you want to "Speed up my system".
If you do not see this window, you can also right click the drive and select Properties.
In the Property window, you have 3 choice. I usually choose the third option Use this device and use the maximum reserved space.
If you want to unplug the device to use for other purpose, you can select "Do not use this device" and then eject the device. Then you can delete the cache file in the device.