Why Actual Memory of Pen Drive Is Less Than Specified Memory?

Recently I bought a pen drive from online store. It is an 8 GB pen drive.

Step 1: Description on the Back

On the backside you can see its an eight GB pen drive.

Step 2: When I Insert Pen Drive in Computer

You can clearly see it shows 7.21 GB free of 7.21 GB. So what about 8 GB?? What happened to 0.79 GB?? We will understand in next step.

Step 3: Explanation for Pen Drive Showing Less Space Than Actual