Flash memory, which has no moving parts, is a type of nonvolatile memory that can be erased and reprogrammed in units of memory called blocks. It is a variation of erasable programmable read-only memory (EEPROM) which got its name because the memory blocks can be erased in a single action or "flash." A flash array can transfer data to and from solid state drives (SSDs) much faster than electromechanical disk drives. Flash is more expensive than spinning disk, however, the development of multi-level cell (MLC) flash has lowered the price of SSDs.
MLC flash is slower and less durable than single-level cell (SCL) flash, but companies have developed software that improves its wear levels to the point where MLC is acceptable for enterprise applications. SLC flash still remains the choice for applications with the highest I/O requirements, however.