USB Flash / SD / uSD / Compact Flash Cards are lightweight, portable data storage devices. Some are used as an alternative to external hard drives for portable data storage. Others are used in cameras and mobile devices to take and store digital photos, videos and other data. Most USB flash drives, secure digital (SD) cards and micro-SD cards use flash memory known as NAND (non-volatile) memory chips along with complex storage algorithms operating on a controller module to quickly store and recall your data as it is written to and read from the device.
An SD card might look like it contains a single chip to the average person but may contain one or more miniature NAND memory chips and a controller module all soldered to a tiny circuit board. In that way, it is similar to the design of a flash drive using a different form factor. The NAND flash memory chip stores all of your data while the controller organizes the storage sectors of the data using complex algorithms. When you plug the SD card into your computer, camera, or another device, data flows to and from the memory chip, organized and managed by the controller, just like a flash drive. The controller keeps track of failing sectors on the NAND chip as one of its many duties. An even smaller version of this, the micro-SD (uSD) card is considered a monolithic device where the memory modules and controller are bonded into a single piece of silicon.
