SSD is an abbreviation for solid state disk. The conventional hard disk does not belong to "liquid" hard disk; solid state disk refers generally to solid state disk composed of NAND Flash. It has no mechanical structure and performs transfer via electronic signal compared to rotational disk design used in conventional hard disks. It utilizes characteristics of conventional NAND Flash and is composed of control unit and storage unit (FLASH chip). Data storage is achieved by the combination of the two units. Data is read and written in block writing and erasing manners. Thus, the efficiency of reading and writing relies on the design with respect to read-write technologies very much. It is advantageous of high speed, low power consumption, vibration resistance, high stability, low-temperature resistance etc.compared to current conventional hard disks.