Hard drives are no longer the objects of mystery and fascination they were in the 1980s—and thank goodness. Plentiful and inexpensive storage has made myriad advances possible that most of could never have conceived of back during home computing's Reagan-administration infancy. But if hard drives are still the storage medium of choice for the vast majority of users and system manufacturers because of their efficiency and affordability, in terms of speed they've been supplanted by an even more dazzling technology: solid-state drives (aka SSDs).

SSDs are based on NAND flash memory, like the kind you'll find in USB keys, memory cards, and music players, rather than the spinning, magnetized platters that hard drives use. This lets them access their data far more quickly than can hard drives, which have to physically track down the information you're looking for. If you have Windows 7 installed on an SSD rather than a hard drive, your PC may boot up in seconds rather than a minute or so. Doesn't sound too impressive? Calculate the number of times you boot your computer in a year, then add all the times you move or copy files, or save large videos or photos, and you'll be shocked at the amount of time you may be able to save.

This speed does not come without compromises, however, and learning what those are—and how to deal with them—is key to finding the SSD that's right for you. Assuming, that is, one is really right for you at all. If you need a lot of storage for your PC, check out PCMag's story "How to Buy an Internal Hard Drive" instead; if you want disk space you can cart around anywhere, "How to Buy an External Hard Drive" contains the advice you're looking for. But if you want the speediest storage possible, and don't mind paying for it—in more ways than one—we'll give you the basic information you need to get solid with solid-state drives.

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How Much Do You Have to Spend?
We don't like reducing every component buying decision to one of money, but with SSDs—as with video cards—there's really no choice. These things are expensive, and the more storage you want, the more you'll have to pay. A 1TB Western Digital VelociRaptor hard drive, spinning at 10,000rpm, is currently available for $270 on Newegg.com, which means you're paying about 27 cents per gigabyte of space. By comparison, the only 1TB SSD Newegg lists is a version of the OCZ Vertex 4, and it costs $2,200—$2.20 per gigabyte. If all you want to pay is $270, you can still get an SSD—but the best you can expect is the 240GB (last-generation) OCZ Vertex 3 MAX IOPS Edition. If you're already thinking these numbers are indefensible, you may as well stop reading this story now. If, on the other hand, you have the money to spare, and are committed to going this route, you'll need to figure out what you'll want the SSD to do.

How Much Storage Space Do You Need?
As SSD prices can rapidly get out of hand, this question is even more vital here than it is when considering hard drives. First and foremost, junk the notion that you're going to put your life on an SSD. You're not. You can't afford it. The only people who can are those in the class of Bill Gates, Warren Buffett, and certain members of the Saudi royal family. The good news is, you don't need to. First, you'll have to abandon the hard drive–centric notion that more space is automatically better. Then, figure out what your truly mission-critical apps are. Your operating system for sure. Maybe Microsoft Office or Adobe Photoshop. If you're really into games (third-person shooters and the like, not the leaner PopCap variety), what are the most common ones you play? Once you know this, determine how much space they take up—if you're using a PC, you can do this by looking at the "Size" column in the "Uninstall or change program" screen in Windows, by investigating the folders in Windows Explorer, or by using a free utility like SpaceSniffer—and you'll know how big of an SSD to seek out. It's smart to leave yourself a little wiggle room, but if you pack all your most important programs into 50GB of space on your hard drive, spending $400 or more on a 512GB SSD is probably going to be a waste. Plan on relegating your lesser-used programs, and all your files, to a spinning hard drive, where you can get 1TB of space for as little as $70. (Note: The amount of storage space available on an SSD is seldom going to be exactly what's advertised. All SSDs require a little bit of space for "overprovisioning," or reserved functions that help the drive work—wear leveling, garbage collection, and so on. A drive that's advertised as 256GB, for example, might have less than 240GB available once it's formatted. This is normal, but it's something that varies from drive to drive depending on features. Reviews will generally tell you what to expect in terms of this difference, and whether it's acceptable or excessive.)

SATA II, SATA III, and I
All consumer hard drives use the Serial ATA (SATA) interface, but that doesn't mean you don't need to pay attention to that line on the spec sheet. There are two different versions of SATA: SATA II, which offers transfer rates of 3Gbps, and SATA III, which pushes data along at 6Gbps. Just as when you're buying a hard drive, faster is pretty much always better, so SATA III is the way to go if your hardware supports it. The good news is that almost all current drives do, but older drives using SATA II are still out there; they'll cost you less, so you'll need to decide whether you'll mind the drop in speed if you get one. It's worth pointing out that a SATA II SSD will still be faster than pretty much any spinning hard drive, but it won't compare to SATA III. (A drive made for one version of SATA will work with the other, but you'll only get the slower speed.)