METHOD 1:

1.Insert the Pendrive in any one your PC USB ports
2.Right click on My Computer and choose properties option
3.The properties window appears, in that choose Advanced system settings option in the left pane
4.Choose Advanced tab in the pop up window and click Settings under performance option
5.Again a new pop up window appears, now select Advanced tab.Click change under virtual memory option.
6.Now uncheck Automatically manage paging file size for all drives feature and select pendrive
7.Enter your pendrive size in both the initial and maximum size boxes and click ok.Both the values should be same.While entering the size don’t enter the actual size of the pendrive.The total space available in my pendrive is 3839MB ( 4GB ) but i have used 3700MB.Always reduce your actual available space by 100 or 200MB and enter the remaining MB for smooth performance.
Restart your pc to use pendrive as a virtual RAM.Without restarting the changes would not take effect.
If you feel that the above method is difficult then you can follow the second method.

METHOD 2:

1.Insert the pendrive in any one of the ports
2.Choose pendrive and right click
3.Select properties and choose ReadyBoost tab
4.Select Use this device and reduce the actual pendrive size by 200MB.Here i have reduced to 3599MB from 3839MB ( almost 250MB ).
5.Click apply.
Sometimes it may throw an error showing ‘your device cannot be used for readyboost’ in such case click test now button or just change the port.
If you no need your pendrive as a virtual RAM then revert back your system settings in to default by enabling Automatically manage paging file size for all drives option in the first method.If you are using second method then you have to select Do not use this device option.