If you want to make a backup of a game you have, or you simply want to store some of your CD's/DVD's on your computer, the best thing to do is to make an ISO file.
This trick won't work on making a backup of a Video-DVD because of the copy protection on it. I use it to be able to run games without a DVD because I use a laptop. For example Black Hawk Down.

To start you want to make a digital CD/DVD, witch is called a ISO and will be stored as "*.iso" on your computer. To do this you will need to have a tool witch is able to do this. I prefer to use "cdrtools frontend" (http://cdrtfe.sourceforge.net/) because it is an easy to use program. After a quick installation you will be able to use this tool.
When you open it, you will see multiple tabs. One of them is called "disc image". On this tab we are going to choose for the option "create image" on the left. Left-click the "browse" button and browse to your DVD/CD driver destination, then open this driver destination. On the right bottom of the screen there is a "start" button, after clicking this button, your computer will start to make the image.

cdrtools frontend
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Now you have the choice, you can either burn the ISO to a new and clean DVD or CD, or you can mount it and make it pretend as a real DVD/CD.

I will first explain how to burn it to a disk.
We are also going to do this with "cdrtools frontend". Go again to the tab "disc image" but now we choose the option "write image" on the right. Left-click the "browse" button and browse to the image you have made earlier. Put the settings as you prefer them (it's smart to put "verify" on) and again press the "start" button on the right-bottom corner. When the burning process is done, you should have a perfect copy of the original DVD/CD.

If you want to digitally run the ISO file you created you will need a second tool, now we will use "winCDEmu" (http://wincdemu.sysprogs.org/). After installing the tool you can go to the folder containing the image, double-click the image file and choose a driver letter for the ISO file, then press "OK". Now a new virtual drive will appear among all other drives in the "computer" folder. Once you are done with the image, right-click on the virtual drive and select "Eject". You can find this tutorial more in detail on their website (http://wincdemu.sysprogs.org/tutorials/mount/).