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Definition: solid state drive

An all-electronic storage device that is an alternative to a hard disk. Employed in myriad products, including mobile devices, iPods, cameras, laptops and desktop computers, solid state drives (SSDs) are faster than hard disks because there is zero latency (no read/write head to move). They are also more rugged and reliable than hard disks and offer greater protection in hostile environments.

Mostly Flash Memory
SSDs are made of flash memory chips. Like a hard disk, flash memory is non-volatile and holds its content without power. In contrast, for the absolute fastest speed obtainable, there are SSDs that use volatile memory chips (DRAM or SRAM) backed up by a hard disk in case of power failure (see nvSRAM and BBSRAM).

Hybrid Drives
Combo drives, such as the Fusion Drive in Mac computers, comprise solid state flash memory and a hard disk (see solid state hybrid drive and Fusion Drive). The hybrid drive is more costly than a hard disk but less than a solid state-only drive. In time, however, there will only be solid state storage, and spinning disk platters will be as obsolete as the punch card (see future memory chips). See disk on module and garbage collection.

Hard Drive Replacement Kits
This Kingston kit includes everything necessary to replace a desktop computer's hard drive with an SSD. Laptop kits include an external case for holding the old drive while it is cloned to the SSD. (Image courtesy of Kingston Technology Corporation, www.kingston.com)

Less Costly Every Year
At one sixth the storage capacity and three times the price of a hard drive, there is a huge discrepancy in cost per byte between the two storage media. However, in 2014, 500GB at USD $349.99 was considerably less expensive for an SSD than just a few years prior. (Images courtesy of Micro Center, www.microcenter.com)

RAM, Battery and Hard Disk
RAM chips provide the fastest access times. This earlier MegaRAM unit contained 4GB of dynamic RAM and a hard disk. In case of power failure, the battery enabled the RAM to be copied to the disk (see nvSRAM and BBSRAM). (Image courtesy of Imperial Technology, Inc.)

GIGABYTE's i-RAM accepts 4GB of DIMM modules for fast storage and keeps it powered with a built-in battery charged on the fly. (Image courtesy of GIGA-BYTE Technology Co. Ltd., www.gigabyte.com)

The First SSD
In 1977, this Dataram module tied eight magnetic core circuit boards together to make the first solid state disk. It held a whopping two megabytes. See core storage. (Image courtesy of Dataram Corporation, www.dataram.com)

Early SSD PC Cards
Minuscule today, these SanDisk 40 and 175MB FLASHDISKs added storage for early laptops. Shown here with CompactFlash (upper left) for size comparison, they plugged into a PC Card slot. (Image courtesy of SanDisk Corporation, www.sandisk.com)