Why do SSDs have a limit rewrites whereas from what I recall, HDs didn’t have this concern? (though they broke often haha) SSD’s have no moving parts, so I’m curious, is it just the current that damages it over time? What happens exactly?
In: Technology
They do have moving parts. Just on a microscopic scale. When you store data on an SSD a current is passed through a semiconductor layer, causing electrons to move. Shifting around these electrons into different positions is essentially what allows you to store data. Now in pretty much every SSD on the market multiple states are stored in every memory cell, which greatly increases the capacity/volume. Generally a modern SSD will have TLC (that is triple layer cells) and store 3 bits for every single memory cell. The problem is that every time you write to a cell on an SSD the semiconductor layer wears out slightly, causing electrons to essentially become stuck. To remedy this, you can just apply a higher voltage, but at some point the additional voltage required to store a certain state in a cell becomes so high, it will start overlapping into the voltage required to store the next state up. This means the two states would no longer be differentiable and the cell is effectively dead.
Because the more layers you store per cell, the narrower these margins are, the higher layer cells you use the less write endurance you get.
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