Definition: SSD write cycle

The measurement of a solid state drive's lifespan. Unlike a hard drive, which can fail randomly, flash memory cells do ultimately fail, although it can take many years. Flash chips incur a minuscule amount of wear each time they are erased and written. With activity, the dielectric layers in the cell retain charges and become less insulative, which ultimately leads to failures. Also called "program/erase cycles" (P/E cycles), "write/erase cycles" (W/E cycles) and "endurance cycles," SSDs that hold more bits per cell have fewer write cycles (see below).

One Write Cycle Is Not One Write
Because flash memory is erased and written in large blocks, one write cycle is not equal to one write from an application. It might take several million writes to cause a drive rated at 100,000 write cycles to start failing. The write cycle metric is also not precise from one drive to the next due to the ways data are managed on the drive. See MLC, TRIM support and flash memory.

   APPROXIMATE RANGE OF WRITE CYCLES

   Type of Cell               Range

   Single Level Cell (SLC)   90-150K

   Consumer MLC (MLC/cMLC)    3-10K

   Enterprise MLC (eMLC)     15-30K

   Trilevel Cell (TLC)        1-5K