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What makes SLC SSDs so special?

“If there is an SSD that stores the data in its most natural way, it will be an SLC SSD.”

SSDs store data in the form of bits inside (microscopic) memory cells. One floating gate transistor makes one memory cell.

In a 250GB SSD, there will be around 2,147,483,648,000 memory cells. (You don’t need to do the maths).

While, a 2TB drive, can have whopping 17,592,186,044,416 memory cells inside it.

Each memory cell will store either 0 or 1 in the form of electric voltage in an SLC SSD. Imagine it as a tiny battery that represents the data based on its charged or discharged state. This battery can be charged and discharged when we write or erase the data into it. Also, the voltage can be checked to retrieve the information in the form of voltage and then interpreted in binary 0 and 1.

For Example, now, you want to store the number 55 inside your SSD. The binary form of 55 will be 110111. So, the controller on the SSD takes the command, takes a page (the smallest writeable unit in SSD), and stores the data in it in binary form. The total consumed space will be 6 cells because of six bits.

On the other hand, the MLC SSDs will store two bits inside one cell. This happens by introducing different voltage levels instead of just high and low. So, there becomes room for adding more binary values inside one cell.

In the TLC drives, there will be room to store three voltage levels within a single cell. This makes room for more data in the same NAND Flash space.

These optimizations lead to faster degeneration of drives but more storage space.

What makes SLC SSDs so special is they are the most reliable drives out there. They are using the most basic method to store the data. We are not overusing the cells and it results in longer life periods. But, their prices are so high that they are used only in server environments and industrial applications.

However, the MLC, TLC, and QLC are for consumer-grade drives. QLC is the cheapest and hence the most unreliable type of drive.

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