Both SSDs and HDDs do the same job: They boot your system, store your applications, and store your personal files. But each type of storage has its own unique feature set. The question is, what's the difference, and why would a user get one over the other? We break it down:
Price: To put it bluntly, SSDs are more expensive than HDDs in terms of dollar per GB. For the same capacity and form factor 1TB internal 2.5-inch drive, you'll pay about $60 to $75 for an HDD, but as of this writing, an SSD doubles that to $130 to $150. That translates into 7 cents per gigabyte for the HDD and 14 cents per gigabyte for the SSD. Since HDDs are older, more established technologies, they will remain less expensive for the near future. Those extra hundreds may push your system price over budget.
Maximum and Common Capacity: As seen above, SSD units top out at 4TB, but those are still very rare and expensive. You're more likely to find 500GB to 1TB units as primary drives in systems. While 500GB is considered a "base" hard drive in 2015, pricing concerns can push that down to 128GB for lower-priced SSD-based systems. Multimedia users will require even more, with 1TB to 4TB drives as common in high-end systems. Basically, the more storage capacity, the more stuff (photos, music, videos, etc.) you can hold on your PC. While the (Internet) cloud may be a good place to share these files among your phone, tablet, and PC, local storage is less expensive, and you only have to buy it once.
Solid State Drive
Speed: This is where SSDs shine. An SSD-equipped PC will boot in seconds, certainly under a minute. A hard drive requires time to speed up to operating specs, and will continue to be slower than an SSD during normal use. A PC or Mac with an SSD boots faster, launches apps faster, and has faster overall performance. Witness the higher PCMark benchmark scores on laptops and desktops with SSDs, plus the much higher scores and transfer times for external SSDs versus HDDs. Whether it's for fun, school, or business, the extra speed may be the difference between finishing on time or failing.
Fragmentation: Because of their rotary recording surfaces, HDD surfaces work best with larger files that are laid down in contiguous blocks. That way, the drive head can start and end its read in one continuous motion. When hard drives start to fill up, large files can become scattered around the disk platter, which is otherwise known as fragmentation. While read/write algorithms have improved to the point that the effect is minimized, the fact of the matter is that HDDs can become fragmented, while SSDs don't care where the data is stored on its chips, since there's no physical read head. Thus, SSDs are inherently faster.
Durability: An SSD has no moving parts, so it is more likely to keep your data safe in the event that you drop your laptop bag or your system is shaken about by an earthquake while it's operating. Most hard drives park their read/write heads when the system is off, but they are flying over the drive platter at hundreds of miles an hour when they are in operation. Besides, even parking brakes have limits. If you're rough on your equipment, an SSD is recommended.