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?
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In an SSD, bit of data is stored in a jail cell with no doors. To get data into the cell, physics magic is used to push the data through the wall. Each time data is pushed into the cell, it requires a bit more power. Eventually there’s not enough power to push through the wall and data can’t be saved anymore.
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.
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.
HDDs work by rearranging some particles using a magnet. You can do that more or less infinite times (at least reasonably more than what it takes for the mechanical parts to wear down to nothing).
SSDs work by forcibly injecting and sucking out electrons into a tiny, otherwise insulating box where they stay, their presence or absence representing the state of that memory cell. The level of excess electrons in the box controls the ability of current to flow through an associated wire.
The sucking out part is not 100% effective and a few electrons stay in. Constant rewrite cycles also gradually damage the insulator that electrons get smushed through, so it can’t quite hold onto the charge when it’s filled. This combines to make the difference between empty and full states harder and harder to discern as time goes by.
I wanted to post eli5 what the diff is between hdd and ssd. Like how is it that 256ssd or whatever is equal to 2T. Does it compact it better?
We say there are no moving parts but thats not actually accurate. There are microscopic switches that work by bending, they eventually fatigue enough to break. Just like bending a paperclip back and forth.
Just to correct your misconception – for all intents and purposes HHDs did not and do not break often. In fact, I doubt there is a mechanical/electric device that you have ever used that has the kind of reliability (factoring in time of use) that HDDs had/have.
wait does this mean that my SSD I need to prepare when they die out?
How do you know when your ssd is getting close to end of life?
Wait… what kind of lifespan are we talking? Like 5 years? 1 Year? Do you get a warning??? I only have one SSD.
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