The Zeus line includes both SLC (single-level cell) and MLC (multi-level cell) drives. SLC is a type of NAND flash in which each cell stores just one bit. MLC allows for multiple bits in a cell, so the same number of cells can store a larger number of bits.

The fourth-generation Zeus products, which are integrated into enterprise storage gear from other vendors, are shipping in sample quantities to the company's OEM (original equipment vendor) partners and should hit the market in the second half of the year, said Scott Stetzer, STEC vice president of technical marketing.

MLC can pack in data more densely than the SLC (single-level cell) technology that is used in most enterprise SSDs. It also costs roughly half as much per gigabyte. But MLC has not been widely used in enterprise storage because it tends to degrade over time when the data stored on it is frequently written over. MLC is commonly used in consumer devices such as portable music players, where new data is not written to the drive as often.

STEC, one of the major suppliers of SSDs to enterprise storage vendors, says the fourth-generation Zeus SSDs with MLC will deliver consistent performance and reliability for at least five years even if all the data on them is rewritten ten times per day. This is the same longevity the company has long guaranteed for its SLC products, Stetzer said.

The MLC drives can achieve this because of advances in STEC's CellCare technology, a combination of hardware and firmware features in the controllers that manage its SSDs. CellCare uses digital signal processing and other technologies to monitor the health of the cells inside the SSD and tune them as necessary to preserve performance. It can get into the cell and block structures of the drive and change the way data is written to or read from it, Stetzer said. STEC's SSDs will also perform error correction when necessary, but CellCare holds off the need for that technique, he said.