USB flash drives have capacities of up to 256 GB (technology keeps increasing the maximum storage capacity), but the most common sizes are 16 GB and 32 GB, which generally offer the best value. Prices generally correspond directly to storage capacity and continue to plummet. In January 2008, the average price per gigabyte of flash-drive storage exceeded $10; however, as the capacity has increased, prices have fallen precipitously. As of August 2010, the average price was a little over $2 per gigabyte in the 32 GB range, with discounts bringing that down to under $1 per GB. In February 2012, that price was down to 63 cents a GB for some budget models.
While 128 or 256 GB USB flash drives conceivably have enough capacity to back up all the files on most people's computers, their small size makes them easier to misplace. External hard drives have radically greater storage capacities (many measure their storage capacity in terabytes rather than gigabytes; 1 TB equals 1,024 GB), and cost considerably less per gigabyte. Flash drives are more convenient for transferring files between computers in a home or office, or taking work to and from your office.
USB flash drives connect via a USB port. If you have a USB 2.0 port on your computer, you'll get transfer speeds of about 30 Mbps. The new USB 3.0 specification claims a maximum transfer rate of 5 GB per second but for USB drives the range is much slower, though still a substantial improvement over 2.0. The Best Reviewed Patriot SuperSonic USB 3.0 flash drive (*Est. $60 for 32 GB), for example, frequently gets 125 Mbps in some benchmark tests, while the same drive plugged into a USB 2.0 port only reaches speeds of 33 Mbps or so.
ReadyBoost is a feature built into Windows Vista and Windows 7 computers that can use one or more USB flash drives to increase performance. Flash drives are faster than hard drives for data transfer, which means recording information on a flash drive can speed some common computer tasks. ReadyBoost is not designed to store files permanently on the flash drive; instead, it borrows the drive, essentially adding extra RAM to the PC for short-term memory while you're working with files.
Windows Vista PCs can use only one flash drive; Windows 7 PCs can use up to eight simultaneously, though only to a maximum of 256 GB of additional memory. Microsoft recommends that the flash drive(s) used for ReadyBoost equal one to three times the computer's RAM. Both Windows Vista and Windows 7 require that USB drives have a minimum capacity of 256 MB, which is well below common USB flash drive sizes on the market currently. The drive must have a minimum speed to be designated as compatible, though it is a speed achieved easily by most USB 2.0 and 3.0 drives on the market: at least 1.7 Mbps write speed and 2.5 Mbps read speed.
You can choose to turn ReadyBoost on or off for a specific storage device. When you plug in a compatible USB flash drive, Windows will automatically prompt you as part of the AutoPlay dialog to determine whether you want to use the drive for ReadyBoost. Speed tests conducted by some sites show substantial improvements for some tasks using the technology.
Most operating systems recognize USB drives without needing special drivers. The simplest USB flash drives show up as a drive on your computer; you can simply drag and drop files to it. Depending on your auto-start settings, plugging in the drive can automatically open a drag-and-drop window.
Many sophisticated USB drives have password protection and/or data encryption. Some USB flash drives include data management software and other extras.
If you only plan to store data on your USB drive, you might want to skip any extra data management software or boot capability, to avoid space-hogging files and hassle.
Reviewers say the following about shopping for a USB flash drive: