What means SLC, MLC and TLC concerning SSDs?

If you have ever wondered what the abbreviations “MLC” and “SLC” concerning SSDs mean, then you will find an answer here. Below we present the different memory types and their characteristics.

In another article we have already dealt with the differences between HDDs and SSDs as well as their advantages and disadvantages. Now we want to go into further detail and introduce various types of SSDs.

The terms SLC, MLC and TLC name the type of SSD memory. They tell you how many bits are written on a memory cell of an SSD.

What do the abbreviations mean?

SLC stands for "Single-Level Cell". As the name implies, an SLC cell stores exactly one bit. MLC means "Multi-Level Cell" and indicates that more than one bit per cell can be stored. Normally, these are two bits per cell, because now also TLC ("Triple-Level Cell") with three bits per memory cell has been developed.

Concerning these three types, Single-Level cells have the highest reading and writing speed. They also require less power, are durable, robust and suitable for an extended temperature range. However, they have only a relatively small memory and are quite expensive. Multi-Level Cell SSDs in contrast have a greater storage density and can store a much larger volume of data.

How does the storage density affect the wear?

MLC and TLS SSDs are often criticized for not being durable enough. As more information is stored per cell, the wear is higher than that of SLCs. For comparison: While manufacturers specify a lifetime for Single-Level Cells with 100,000 write cycles, Triple Level Cells only bear 1,000 writing processes. MLCs are at about 5,000 to 10,000 cycles.

This sounds comparatively low, but is usually absolutely sufficient. Thanks to techniques such as wear leveling, almost no one has to worry about the durability of his SSD.

What is wear leveling?

Wear leveling is used to extend the life of an SSD. The technique is often integrated in SSDs.  With an algorithm the write cycles are distributed homogenously, so that all memory cells are equal and that the SSD wears evenly.

This technique is distinguished between dynamic and static wear leveling. The former only distributes dynamic data, thus those that change when something is deleted and something else is saved. To prevent some cells from being described only once, while other cells fail already, static wear leveling algorithms move the static data to other blocks. The dynamic variation is often found in USB flash drives. With SSDs the static wear leveling is most commonly used.

What kind of SSDs does spo-comm sell?

As standard spo-comm offers Multi-Level Cell SSDs in different sizes, since these provide a high storage volume for a reasonable price. Some PCs (such as the WINDBOX and RUGGED series) can also be ordered with a 16 or 32 gigabyte SLC SSD. These are suitable for an extended temperature range of -40 to 85 degrees, but – despite the low storage density – are found in an upper price range.

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