Solid State Hard Disk: Solid State Disk (English: Solid State Disk or Solid State Drive, abbreviated SSD), also known as solid-state drive, is a permanent memory [such as flash] or non-permanent memory [such as synchronous dynamic random access memory (SDRAM)] based on the computer's external storage devices. Solid state drives are used to replace conventional hard disks in portable computers, and although there is no longer a rotatable disk structure in solid state drives, this type of memory is still referred to as a "hard disk" in accordance with people's naming conventions. Solid state drives are widely used in military, automotive, industrial control, video surveillance, network monitoring, network terminals, power, medical, aviation, navigation equipment and other fields.