I am looking for a free open source disk software which can be used to make virtual RAM disk as I have 16GB of RAM and I want to use some of it as virtual disk for storing frequently accessed stuff faster. Let me know how can do it ? I am looking for free version , I tried DATARAM but its not free and I am not willing to spend money as its just for experience purpose.

You can try imdisk, it is a open source RAM disk creator, it is also one of the efficient one. It also lets you create virtual disk out of image files.