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
The failure mechanism for HDD was more of a wearout of the motor or bearings and less of a wear out of the platter itself because it was just changing the magnetic field of particles.
SSDs use flash with a “floating gate transistor” and we store values by injecting charge onto that floating gate. But how do you get charge onto a floating gate? You use enough voltage to punch the electrons through the insulators that keep it floating
Each write cycle damages the insulator a little bit causing it to break down over time until the electrons on the gate are free to escape so you can’t reliably store bits on it.
For most SSDs though lifetime isn’t a huge concern, you can write about 1 PB of data onto a modern 1 TB SSD before it starts wearing out. SSDs are also built with spare blocks that it doesn’t show you, so your 1 TB SSD may come with 1.2 TB of flash and it’ll rotate that extra 0.2 TB in as existing blocks get too many writes on them to extend the life of the drive as a whole.
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