One disadvantage of multi-level cell flash is its higher bit rate in comparison with NAND flash memory and a single-level cell. The more bits a cell contains, the fewer write cycles it can handle, and the greater the possibility of errors. Single-level cell flash uses NAND memory of best quality, storing 1 bit per cell but always in one of two voltage states programmed, denoted as 0 and 1. Having only two states means that in single-level cell flash allows for fast data analysis and decreases bit error rate. Since SLC flash stores fewer data bits per cell, however, it is typically considered a more expensive form of storage memory than multi-level cell flash.
The ability to multiply multi-level cell flash voltage states decreases manufacturing costs and has increased the use of technology in mobile phones, cameras and USB flash drives. Usually, MLC flash memory cards have a slower transfer speed and use more power. A multi-level cell is divided into four states, defined by the cell’s degree of electrical charge. The MLC has two levels, the MLC-3 has eight, and the MLC-4 has 16.
Allowing multiple electrical states can also lead to higher error rates with multi-level flash cells. When a NAND flash cell exceeds its write limit, it will begin to a malfunction that can corrupt data. To make this, vendors tried to solve the issue by developing smarter flash controllers.