What is SLC flash memory?

SLC stands for Single Layer Cell and is flash memory with a single “story” of memory and each cell has two possible states (state = a voltage level) with each state representing either a one or a zero. SLC memory has the advantage of higher write speeds because there is less time for a computer system ro access the cell for a read or write function. There is also less power consumption because the amount of power to change the state is also reduced because of only one “story” required to access or change the cell. SLC memory is the most expensive type of flash memory and harder to source.

A single-level cell (SLC) flash memory may have a lifetime of about 50,000 to 100,000 program/erase cycles.

Today, most consumer products are MLC flash memory or Multi Level Cell flash memory. In February 2016, a study was published that showed little difference in practice between the reliability of SLC and MLC flash memory. Because SLC memory stores less data per cell than MLC memory, it costs more per megabyte of storage to manufacture, this report and the real-world experince with longevity is one reason MLC is more prevelant than SLC flash memory.

To boil it down into simple terms, picture the size of a stamp…now, that size can be used as memory and a Single Layer Cell flash memory will hold what can be stuffed into that sized stamp, but Multi Layer Cell flash memory can double that capacity yet stay at the same physical size. Or x2. The advantage to using MLC is reducing the cost of memory production, suddenly you have twice the capacity at the same price, which is a big advantage for flash drive manufacturers. It allows the company to offer larger memory storage products at cheaper prices. Of course there is a hook.

A significant portion of the flash-based memory devices on the market today are made from MLC flash and the continuing growth of flash drive products can be considered an indication that the performance is meeting consumers’ needs. However, since the use of MLC technology offers the highest density there is a tradeoff, and you guessed it, a tradeoff of lower performance. Lower performance in the form of slower write (and potentially erase) speeds, as well as reduced write/erase cycling endurance. In addition, life expectancy of SLC flash is rated at approximately 100,000 cycles and MLC flash is rated to have approximately 10,000 cycles. That’s 10 times longer with SLC based products. However, in many cases, 10,000 erase cycles is more than sufficient for the life cycle of the product.