Just think about what QLC means and you will say this is crazy. You have a nand cell (transistor) and put some charge on its gate and hope it will stay there. It does, ok, we are happy we can read it back. Then you think let's double the capacity and store 2 bits in a single transistor. Yeah, ok, but that requires to divide the charge level to 4 bands and introduce 2 more compare levels, ok, that's fine, we lost some SNR on the way but we will compensate it with more robust ECC. Then come the greedy butheads and say, hey, if it goes that way, why don't we work with 4 times that level??
Do it for us, friend we must increase the density on market demand.
yeah, just thinking, if the full level is converted to voltage and you get 1V as max, bellow 0.5 is 0, above it is 1, doable (SLC)
let's go QLC:
0 - 1/16 is 0
1/16-2/16 is 1 and so on, it sounds good doesn't it?
well, that makes about 62mV bands, which you need to discriminate during read. it leaves you with very low noise immunity.
in general, if you want to make an N-fold increase of density, you will have a 2 ** N impact on the tolerances.
each transistor has a transfer function that will distort the readout value as well. Yeah, they can probably make very good matching transistors, but still, when the demand makes the tolerance so braindead tight...
Luckily the engineers managed to solve all of the problems so we can start selling our new, fancy, hypercapacity NAND chips.
what? it can only be written 2-300 times? psst, let's give it a fancy name and hide that detail between the NobodyKnowsWhatItMeansButSoundsVeryGood parameters, let's call it QLC, wow it is not a boomer SLC shit, this is a QLC!!! a QVO ... a whatever.
And the crowds buy it blind.
and that's why there will be no reliable storage in some years, I would be happy with MLC but it is completely finished too...
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