It's possible to have single stranded DNA, but you'd have problems with error correction. Let's say DNA breaks, or some errors appear in the code. Thanks to th

It's possible to have single stranded DNA, but you'd have problems with error correction. Let's say DNA breaks, or some errors appear in the code. Thanks to the double stranded structure it's "quite easy" to repair the code. Besides that, it's not the density which is a problem right now, but the access speed. The amount of data in DNA is so immense that doubling the density won't give any practical improvements for decades to come - if ever. Having said that, if I'm not mistaken, some viruses are encoded by single stranded DNA & ssRNA. I'm not sure, but the density might be the reason for that.