Today the SSD is slowly replacing the HDD in computers. Not only is the SSD faster, it is of particular benefit in laptops, where moving and jarring a laptop won't bother an SSD but could be disastrous for a spinning HDD. If you'd like to learn more about SSDs, here and here are two excellent articles from ArsTechnica. The first article discusses the need for TRIM (a wear-leveling technique) in SSDs. The second article gives an in-depth discussion of SSDs and how they function. Both articles are for technophiles. Casual users need not read (unless, of course, you want to).
While I enjoyed both articles, I must admit my understanding of the second article left something to be desired.