The PC World Test Center evaluated eight SSDs and found that performance diverged widely among them, as well as compared with magnetic hard-disk models. To see the test results for the top five SSDs, consult our .

Until the advent of SSD, standard PC storage relied on magnetic hard-disk technology, which has numerous moving parts (including a spindle motor, an actuator assembly, and read/write heads that float barely 10 nanometers above the spinning platter surface).

By contrast, SSD storage consists of NAND flash-memory chips. SSD's lack of moving parts gives it an edge over regular drives on multiple levels. First, SSDs are more shock-resistant than magnetic hard-disk drives; SSDs have fewer potential points of mechanical failure, and are able to withstand jostling and sudden impacts. Second, SSDs are silent, which makes them great for PCs that sit in living areas. They also generate less heat and use less energy, so they don't require fans, which contributes to their quiet operation as compared with a spinning hard-disk drive. Finally, because of their compactness, SSDs can be designed to fit in tight spaces.

That said, today's SSDs primarily adhere to the current 1.8-inch and 2.5-inch hard-disk sizes, and typically they use the same connectors as hard-disk drives do (first Parallel ATA, now Serial ATA-300). An SSD can easily fit into a current laptop or desktop chassis using existing industry standards. As a result, buyers should think of SSDs not as replacements for regular hard-disk drives but as complements to them.

In , SSD currently has little hope of competing with standard hard drives, and this won't change anytime soon. Expect to pay upward of $2.75 per GB for an SSD, versus about $0.25 per GB for a regular hard drive. Capacity remains relatively limited, too: 256GB is the current high end for mainstream SSDs. (A few outliers, such as the , reach 500GB or even 1TB, but they have a stratospheric cost and come in a 3.5-inch chassis.) Because of that limitation, SSD makers don't target storage-hungry users. If you need high capacity, look to standard ; they can offer more than triple the capacity of SSD at a fraction of the price. (Another possibility for desktop PC owners who want the best of both worlds: Use an SSD as the primary boot volume for your apps and operating system, and use a roomier regular hard drive to store data.)