Step1:- To create pendrive as virtual RAM you need a pendrive of minimum 4GB.
Step2:- Insert your pendrive into your pc
Step3:- Take backup of your important data, during process may be delete your data.
Step4:- Right click on drive ,select "Format" option and then click on "Start" button to format your drive.
Step5:- When format completed, again right click on drive , select "Properties" option.
Step6:- Now select "ReadyBoost" option.
Step7:- Select option "Use this device" then click on "Apply" button and then click on "OK" button.
Step8:- Reboot your computer, to apply changes on your computer.
Warning:- Do not format or remove this drive before disabling ReadyBoost. To disable ReadyBoost , right-click on drive, select Properties, choose ReadyBoost, and then choose Do not use this device.
If you got any error during this process then put it on comment, Let me know about your the error.