MLC vs. SLC

In the world of non-volatile storage media, flash is a relatively new technology that has quickly carved its niche, and is even beginning to replace traditional hard drives, due to significant performance advantages. There are two types of NAND flash memory, SLC (Single-Level Cell) and MLC (Multi-Level Cell). The major difference between the two, is the way they store information. SLC stores each bit on its own discrete memory cell, while MLC stuffs two bits into a single memory cell. This difference creates major changes in certain aspects.

Since MLC can place double the amount of data in each cell, it has twice the data density of a comparable SLC memory. This means that you can either use a smaller amount of silicon for a given capacity, or twice the amount of data with the same amount of silicon. As the price of a flash based memory is based largely on the amount of silicon material being used, we can clearly see that you get a much lower price per MB with MLC flash memory, than with SLC. MLC makes flash based memory cheap enough to be within the reach of most consumers. Most consumer level Solid State Drives (SSD) and flash memory use MLC, while those on the high-end are SLC.

The biggest motivator for using SLC, despite the exponentially higher price, is its performance. SLC drives have much higher read and write speeds, because, having a dedicated memory cell for each bit, is much simpler compared to having two. SLC also has a reduced probability of writing errors, thereby lessening the possibility of the data needing to be rewritten. When it comes to the life span of the drive, SLC drives have the advantage. The extra writes incurred by MLC based drives, due to the additional bit, results in the flash memory failing much faster compared to SLC drives. Although MLC drives might fail sooner than SLCs, their life span is still long enough to suffice for the needs of most consumers.

Summary:

1. SLC stores a single bit for each memory cell, while MLC stores 2 bits for every memory cell.

2. SLC has a lower data capacity compared to MLC, given the same amount of semiconductor material.

3. SLC costs considerably more than MLC.

4. SLC performs a lot better compared to MLC.

5. SLC lasts longer compared to MLC.

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