First you need to go to the Device Manager which you can go directly by just typing device in the start menu search box or just type in devmgmt.msc in command line.
Now open the Disk drives section and right click on your hard drive. Now click on the Policies tab and you’ll find this dialog box:
Now click the checkbox for Enable advanced performance, and you are done.
Write caching isn’t enabled by default as removing devices directly without using the “Safely remove removable device”may lose your data, so be cautious when enabling this options. But enabling this option also when speeding up performance significantly when writing to the disk.
Now select the external drive and double click it to open up the properties screen. Then
just change the setting to “Optimize for performance” and hit OK to continue. You’ll have to reboot for all the settings to take effect. Next time you boot into Windows Vista you’ll see faster bootup times and better disk writing performance.