Skip to main content

SLC, MLC etc.

There are different types of flash memory:

SLC (short for single-level cell) are memory cells that consist of NAND flash and each stores one bit. Only two charge- states per capacitor are used here. This construction enables the highest data integrity and is used because of the higher reliability with write-intensive memory requirements.

pSLC  (pseudo single level cell) is the latest innovation in industrial flash memories. This is based on MLC-NAND (Multi Level Cell), but the NAND cells are operated like an SLC memory. Instead of two bits as is usual with MLC, only one bit is stored per NAND cell. In addition, the differences between the voltage levels are significantly greater than with conventionally operated MLC-NANDs. As a result, pSLC memories achieve six times more write and erase cycles than conventional MLC memories.

For industrial applications with high storage requirements, which nevertheless place high demands on service life and functional reliability, pSLC storage can be an attractive alternative. However, it is a misconception that pSLC storage can approach SLC storage. Genuine SLC storage systems have up to five times longer service life (endurance) than pSLC storage systems

MLC memory cells (MLC is short for multi-level cell) are memory cells in which more than one bit per cell is stored. The storage of several bits per memory cell has the disadvantage that the reading and writing speed is generally lower. The cells react much more sensitively to charge losses. Low charge losses of 10 percent, which are of no importance in SLCs, cause bit errors in MLC cells. The same error correction procedures are used as in SLCs, but with a higher contingent of correction data, which again reduces the gain in capacity somewhat.
This technology is significantly cheaper than SLC memory and is mainly used for read-intensive memory requirements.

Older storage technologies:

aMLC (short for advanced-multi-level cell) is a technology developed by ATP that tries to integrate the advantages of SLC in an MLC cell. It significantly increases the performance and longevity of conventional MLC flash. The principle behind it: Ordinary MLC memory is modified at firmware level so that instead of the usual four charge states per memory cell, only two are used. In principle, the MLC memory then works in SLC mode, which offers a higher write speed and also allows more write cycles. The write performance is close to that of SLC memory. The number of possible write cycles for MLC is approx. 3,000 P / E cycles, and for aMLC 40,000 P / E cycles.
aMLC was superceded by pMLC (see above)