How to create a windows 7 installation disk from windows 7 which is already installed?

-I had windows 7 on my PC preinstalled, when I bought it. Recently, my system crashed and wouldn't boot. On searching for my re-installation disk, i discovered that I had lost it. Though I recovered my system using start up recovery, I was thinking that if any greater damage would occur in near future, I would be totally helpless. So, I want to know if I can create a new installation disk from my installed windows 7.google it