Some file systems are designed to distribute usage over an entire memory device without concentrating usage on any part (e.g., for a directory) to prolong the life of simple flash memory devices. Some USB flash drives have this 'wear leveling' feature built into the software controller to prolong device life, while others do not, so it is not necessarily helpful to install one of these file systems.[39]
In a typical well-conducted review of a number of high-performance USB 3.0 drives, a drive that could read large files at 68 MB/s and write at 46 MB/s, could only manage 14 MB/s and 0.3 MB/s with many small files. When combining streaming reads and writes the speed of another drive, that could read at 92 MB/s and write at 70 MB/s, was 8 MB/s. These differences differ radically from one drive to another; some drives could write small files at over 10% of the speed for large ones. The examples given are chosen to illustrate extremes....′[46]
The 32GB capacity of this SanDisk Ultra SDCZ48-032G-A46 flash drive provides ample room to store photos, music, videos and other files. The USB 3.0 interface and up to 80MB/sec. read speed make it easy to transfer files to and from your computer. (Ten times faster than USB 2.0 drives. Write speeds up to 10 times faster than Cruzer USB 2.0 drive.)* *USB 3.0 port required. Based on internal testing; performance may be lower depending upon host device.

Some manufacturers, aiming at a "best of both worlds" solution, have produced card readers that approach the size and form of USB flash drives (e.g., Kingston MobileLite,[65] SanDisk MobileMate[66]) These readers are limited to a specific subset of memory card formats (such as SD, microSD, or Memory Stick), and often completely enclose the card, offering durability and portability approaching, if not quite equal to, that of a flash drive. Although the combined cost of a mini-reader and a memory card is usually slightly higher than a USB flash drive of comparable capacity, the reader + card solution offers additional flexibility of use, and virtually "unlimited" capacity. The ubiquity of SD cards is such that, circa 2011, due to economies of scale, their price is now less than an equivalent-capacity USB flash drive, even with the added cost of a USB SD card reader.
USB 2.0 flash drives have a transfer rate of up to 480Mbps, while USB 3.0 flash drives allow for transfer rates 10 times faster — up to 4.8Gbps. However, you can only take advantage of this higher speed if your device has a USB 3.0 port. Although USB 3.0 flash drives and other devices are backwards compatible with USB 2.0 ports, they will only operate at a USB 2.0 rate.
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