Once upon a time a CD was large. Huge. You used it to save lots and lots of data.
Then came MP3s, movies, digital cameras with millions of pixels and suddenly the CD was small. And the DVD came, and for a while it was large... I don't think it ever was huge.
Today I would have to use more than 300 4.4 GB DVDs to save all my data, and that only includes the data on hard drives. Making back-ups becomes a question of selecting what to back-up and what to leave for chance. A real pain.
But there might be light at the end of the tunnel.
This is (layman's interpretation) done by using holograms. The disc is transparent (wonder how that will work with labeling?) and uses ten layers of data (to compare with blu-rays that use two, and ordinary DVDs that use one). Anyway, sometime around 2010 they might be able to fit as much as 1 Terabyte to a CD-sized disc.
That's probably the same time as hard drives comes in 10-20 Terabyte sizes, and soon after the 1TB DVD will once more be insufficient.