Buying a solid state hard drive is about more than just pure gigabytes. It’s critical to consider other factors such as speed and drive lifetime, as well as making sure the drive will fit in your intended device.
Solid State Hard Drives Verses Non-Drives
Both solid state hard drives and SD cards use exactly the same storage technology, but that doesn’t mean they’re compatible. If your laptop includes a built-in card reader, you can’t just buy a 32 gigabyte SD card and start using it like a hard drive.
The reason for this is simple: card readers require special drivers that are almost never loaded into your computer’s BIOS (or UEFI), so your computer can’t boot off of an SD card. Also, Windows and Mac OSX treat SD cards somewhat special, so you’ll face many additional hassles using them as generic data storage.
USB thumb drives also use the same technology and, unlike SD cards, your computer recognizes them as real drives. Using any computer built in the last five years, you can boot off of a thumb drive with no problems (although you may need to reconfigure your BIOS settings first).
Thumb drives protrude from your computer, so they can be less than ideal, although if you’re in a pinch, you can use a tiny thumb drive that only sticks out a little bit. These tiny thumb drives are great for users of netbooks and laptops who want an additional drive but don’t have anywhere inside the computer to put it.
Finally, there are real solid state hard drives—drives that are designed to either go inside your computer or to operate as external drives. These usually offer the best value per gigabyte because their extra size allows them to use bulkier but more affordable solid state parts.
External Versus Internal
Internal drives are almost always slightly more affordable than external drives (all other things being equal) because they don’t need a special case. External drives are more convenient if you only need to connect the drive occasionally, such as for backups.
Whichever option you choose, drives are generally equivalent—in fact, you can almost always remove the case from an external drive and use it internally, or buy a case for an internal drive and use it externally. Also see our external hard drive buying guide for more details.
Internal Solid State Hard Drive Size
If you buy a hard drive for internal use, it’s absolutely critical that you buy the correct physical size. For laptops and many other small devices, the standard size is a 2.5-inch drive. For desktops, the standard size is a 3.5-inch drive. You can buy a $5 adapter to put a 2.5-inch drive inside a 3.5-inch desktop drive bay, but of course you can’t fit a 3.5-inch drive inside a 2.5-inch laptop drive bay.
When buying a drive for a specialty device, such as a TiVo or netbook, you must research the device’s specifications, or you must open the device and find what size drive it currently uses.
Solid State Versus Hybrid
Hybrid drives are advertised as providing the high-capacity storage of a traditional magnetic drive along with many of the speed benefits of a solid state drive. Unfortunately, they also have the problems of both drives: when either the magnetic or solid state part dies, the whole drive dies, so hybrid drives are best used if you really need the high capacity and fast speed but don’t have the ability to have separate magnetic and solid state drives. (Perhaps because you have a laptop with only one drive bay.) See this article: The pros and cons of hybrid hard drives.
Solid State Speed
Speed is a critical consideration when purchasing a solid state drive—different drives have different speeds. Worse, almost all drives read and write data at different speeds, so opening a file may be quick but saving that same file may be slow. There are three measurements you should use to compare different drives:
- Read Speed: this is the most important for typical computer users as it determines how fast your files and programs will open, so faster speeds mean less waiting. Traditional magnetic hard drives tend to top out around 150 megabytes (MB) per second (MBPS). Cheap USB thumb drives get between 8 MBPS and 20 MBPS; low-quality solid state drives get 300 MBPS or less; good drives currently get around 500 MBPS.
- Write Speed: although this seems important, it usually isn’t for typical computers—if your computer has to write a file, it’s usually already in your computer memory, so your computer can perform the write operation in the background without taking up any of your time. That’s good because solid state drives often have write speeds that are slower than their read speed. In general, look for a drive with a write speed that is at least 75% of its read speed.
- Non-Sequential Reads: (also called Random Reads) score how well the drive reads fragmented files or two unrelated files that both need to be opened at the same time. As this is something that happens quite often in reality, this is an important score—so be careful of drives that don’t list it in their specifications. Random Reads are scored in Input/Output Operations Per Second (IOPS) or 1,000 IOPS (KIOPS), which is how many times the drive was able to read data in a single second. Traditional magnetic hard drives are very slow because they need to physically move the read head, but good solid state drives should get 75,000 IOPS (75 KIOPS) or more.
Although the number of gigabytes a drive stores is often the first thing people consider, it should probably be the last thing on your list to consider—find a good drive that matches your computer and your needs and then try to find it in the right capacity. Solid state drive prices keep coming down on a per-gigabyte basis, so you should shop around a little to try to find the best deal.