What is a Double E savings bond and how exactly does it work?

My father was telling me about this savings bond that you can buy any amount and after 5 years the value is doubled. If this is so, then why wouldn't everyone just use these instead of risky stocks? What would the disadvantages be of these savings bonds, and is there something really better than this that does not involve risk?
I didn't say it doubled EVERY 5 years. Well, he said it doubled after 5 years and then after that it just grows little by little. He mentioned that he had a friend who bought a 5,000$ bond back in the 70's and forgot about it but when he casked it a few years ago he received 40,000$.

How much is the interest right now? Like if I were to buy one for 100$, what would it gain after that 6 months and what would the maturity date be?
Purchase in denominations of $50, $75, $100, $200, $500, $1,000, and $5,000, and $10,000.
$5,000 maximum purchase in one calendar year.

Thats what that site says… but how would you purchase a 10,000$ bond but you cant buy more than 5,000$ in a year? weird…

Here you go.

http://www.savingsbonds.gov/indiv/research/indepth/ebonds/res_e_bonds.htm