this post was submitted on 04 Aug 2023
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Explain Like I'm Five
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so people have said that it’s to do with volatile (it forgets) and persistent/non-volatile (it remembers), but i think the crux of your question is a little more nuanced: WHY does the mechanism to “remember” a 1 or a 0 get damaged with SSDs and not for RAM
now, i’m not expert here but i think i have a basic understanding and i’ve pieced some bits od research together!
(edit: it should be noted that what ive described here as simply “RAM” is actually SRAM, but modern computers mostly use DRAM which is different: it uses a capacitor instead of a couple of transistors, but the fundamental idea is the same)
RAM is very simple: for the most part, it’s just a few transistors - they’re basically little switches that work just with electrical current… they can be arranged so that transistors connect to another transistor, so that they’re both telling each other to be “on” (this is SUPER simplified, but kinda think of the electricity being stuck in a loop: it just goes round and round between the transistors, and that’s “on” or 1)… transistors are very reliable! their chemistry doesn’t degrade over time (note though that because electricity doesn’t actually go around in an infinite loop, if the “loop” stops getting power to replenish it, it resets to 0, which is what makes it volatile!)
SSDs though store their 1s and 0s more in chemicals… think of your SSD like a bunch of little boxes with water in them, and you read the 1s and 0s based on how clear the water is… you add sand to make a 1, and you filter out the sand to reset it to a 0! the more often you do that though, the dirtier the water gets until you can’t tell if it’s just dirty water of if it has sand in it (actually you add electrons to the gates in an SSD which changes the cells resistance and you read based on that, but at some point the electrons just keep ”sticking” in the cell so the resistance doesn’t change as much as we’d like)
SSDs typically use flash memory, as I understand it. I'd leave the sand out and say it's like a tank you fill up with (more or less depending on the data) water. After a while the tank mechanically wears out and starts to leak. Flash memory very much is like a tank filled with electricity and then plugged, and it does start to leak as the insulating oxides degrade.
oh I get it. since transistors can't hold charge when machine is off data in RAM go away. and since SSDs store data chemically power status doesn't affect the storage. nice