Solid-state drive
A solid-state drive (SSD, also known as a solid-state disk although it contains neither an actual disk nor a drive motor to spin a disk) is a solid-state storage device that uses integrated circuit assemblies as memory to store data persistently. SSD technology primarily uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives, which permit simple replacements in common applications. Additionally, new I/O interfaces, like SATA Express, have been designed to address specific requirements of the SSD technology.
SSDs have no moving mechanical components. This distinguishes them from traditional electromechanical magnetic disks such as hard disk drives (HDDs) or floppy disks, which contain spinning disks and movable read/write heads.Compared with electromechanical disks, SSDs are typically more resistant to physical shock, run silently, have lower access time, and lower latency. However, while the price of SSDs has continued to decline over time,consumer-grade SSDs are still roughly four times more expensive per unit of storage than consumer-grade HDDs.
As of 2015, most SSDs use MLC NAND-based flash memory, which is a type of non-volatile memory that retains data when power is lost. For applications requiring fast access but not necessarily data persistence after power loss, SSDs may be constructed from random-access memory (RAM). Such devices may employ batteries as integrated power sources to retain data for a certain amount of time after external power is lost.
Flash-based SSDs
In 1989, the Psion MC 400 laptop included four slots for removable storage in the form of flash-based "solid-state disk" cards, using the same type of flash memory cards as used by the Psion Series 3.[24] The flash modules did have the limitation of needing to be re-formatted entirely to reclaim space from deleted or modified files; old versions of files which were deleted or modified continued to take up space until the module was formatted.
In 1991, SanDisk Corporation created a 20 MB solid state drive (SSD) which sold for $1,000.
In 1994, STEC, Inc. bought Cirrus Logic's flash controller operation, allowing the company to enter the flash memory business for consumer electronic devices.
In 1995, M-Systems introduced flash-based solid-state drives. They had the advantage of not requiring batteries to maintain the data in the memory (required by the earlier volatile memory systems), but were not as fast as the DRAM-based solutions. Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications. These applications require the exceptional mean time between failures (MTBF) rates that solid-state drives achieve, by virtue of their ability to withstand extreme shock, vibration and temperature ranges.
In 1999, BiTMICRO made a number of introductions and announcements about flash-based SSDs, including an 18 GB 3.5-inch SSD.
In 2007, Fusion-io announced a PCIe-based SSD with 100,000 input/output operations per second (IOPS) of performance in a single card, with capacities up to 320 gigabytes.
At Cebit 2009, OCZ Technology demonstrated a 1 terabyte (TB) flash SSD using a PCI Express ×8 interface. It achieved a maximum write speed of 654 megabytes per second (MB/s) and maximum read speed of 712 MB/s.
In December 2009, Micron Technology announced an SSD using a 6 gigabits per second interface.
