A computer storage device constructed out of solid-state NAND flash circuits. SSDs have the same connections and follow the same data-transfer protocols as conventional magnetic disk hard drives, and are a form of nonvolatile memory, so can be used as plug-in replacements. Their cost per bit of storage is higher than that of hard disks, but the data rates they can handle are much higher. Increasingly, SSD drives are offered as a high-end option when purchasing personal computing devices.