Comment by tliltocatl | Hacker News Reader

Comment by tliltocatl | Hacker News Reader

I think the article is wrong in its core premise. While the electrons get added or removed from the floating gate, the total number of electrons in the SSD chip stays the same. Gates are capacitors, in order to add electrons to one capacitor plate, you have to remove an equal numbers of electrons from the other plate, i. e. from the transistor channel. The net charge of a SSD chip is always zero. Otherwise it would just go bang. <s>2.43×10^-15</s> [my bad 1] 2.67×10^15 electrons is about 300µC - that's a lot of charge to separate macroscopically.

Therefore the mass (weight is a different thing, through it is proportional to mass at a given constant gravity potential) of the data on a SSD isn't fundamentally different from a HDD - they both are caused by a change of internal energy without any change in the number of fermions. I'd expect data on SSD to have larger mass change because a charged capacitor always store more energy than a discharged one, while energy of magnetic domains is less directional and depends mostly on the state of neighbor domains - but I'm not sure about this part.

[1] Thanks stackghost.

> So, assuming the source material is correct and electrons indeed have mass, SSDs do get heavier with more data.

That is definitely wrong! No way the source material has more electrons. The only way it could do that is by being charged.

Richard Feynman, The Feynman Lectures: "If you were standing at arm's length from someone and each of you had one percent more electrons than protons, the repelling force would be incredible. How great? Enough to lift the Empire State Building? No! To lift Mount Everest? No! The repulsion would be enough to lift a "weight" equal to that of the entire earth!"

From: https://tycho.parkland.edu/cc/parkland/phy142/summer/lecture...

Not sure I'd survive that experiment.

See, now, if this was Reddit...this is the opportunity for a yo momma joke. But here we are on HN, so I'll just point out that this is the opportunity for a yo momma joke.

Yo mamma is so fat she broke the Coulomb barrier?

Well done.

>2.43×10^-15 electrons

I believe TFA reads 2.43×10^-15 kg, not electrons. Unless SSDs are creating new and exciting physics, one can't have less than one electron, as it's an elementary particle.

Neutrinos weight far less than electrons (but while NAND flash involves super weird physics it's not that weird)

They do weigh far less, but a quantity of "10^-15 electrons" is still impossible.

10^–15 is not a negative number, just a small one. https://www.wolframalpha.com/input?i=10%5E-15+

And it is less than one?

I think my favorite part of that comment is "documenting" that 10^(-15) is not negative by appealing to Wolfram Alpha.

your user name is found at the 4,922,096,564th digit of Pi

Good thing he didn't say that

Yes, you're correct. Now ask yourself if "one quadrillionth of an electron" is a quantity that's possible to have.

Well you could have a virtual particle whose mass could be time-averaged.

> energy of magnetic domains is less directional and depends mostly on the state of neighbor domains

Yes, but it's the same thing. The flux changes on the drive define the bits. It's probably true that a drive storing all 1's or all 0's would be quantitatively (but surely immesurably) lighter. But in practice a drive storing properly compressed high-entropy data is going to see a flux change every other bit on average. And all of those are regions of high magnetic field with calculable energy density. Same deal as charge in a capacitor, which also stores energy in the field.

Exactly. On top of that, most managed flash (which is equivalent to SSD controllers) will pass all write through a modified cyclic XOR pad in order to keep the /bit/ entropy high. I don’t think the article holds on multiple abstraction layers.

Which is the same reason storing data to a HDD doesn't add weight. You can pack the data tighter if you are writing basically balanced 1s and 0s. Thus you can pack more bytes into a given area by encoding them into patterns with even distributions even though that means you need to write more bits.

But SSD erasing must write a constant (either one or zero). So an erased ready-to-write SSD block will have consistently different energy than one written with a random scrambled pattern. Same for SMR HDDs - but not for CMR.

The SSD lies :) TRIM is a scam.

What happens when you XOR a 0 with a byte in a one time pad? You get the corresponding byte from the pad, right? And the block full of 1s or 0s is exactly a case the scrambler needs to be used.

It's not for compression or anything like that, it is used because the cells are packed so tightly that sharp changes in energy gradients over the space will even themselves out by donating electrons to their neighbors (flipping bits). It's kind of like rowhammer.

Instead of just a ont-time-pad, a more complicated and often proprietary scrambler is used. But it's towards the same end. It's a deterministic, pseudo-random bit sequence.

If you can bypass the controller (read directly from NAND) you will see the true values that it returns, and it will likely be scrambled even if the flash controller reports otherwise. This also allows you to recover the scrambler, since you know that the other side of the XOR operation is 0.

Trim might be an illusion, but block erase is very real, even through it's not exposed as a device command. What I'm trying to tell, writes are scrambled but erases (not trim which marks a logical block as collectable, but physical erase that makes a physical block writable) aren't as they happen over several megabytes at once with no way to control individual bits.

Oh yes you’re right, I did neglect physical block erase which does happen outside the data path.

Another bit I’m surprised seems to have gotten completely glossed over: there is a deep relationship between _entropy_ and mass which puts bounds on the amount of information you can place in a given volume.

TLDR: a given region of space can’t have more entropy than a black hole of the same volume. Rearranging terms, you find that N bits of information (for large N) has an equivalent black hole size, which in turn has a mass…

TFA started out seeming well enough written but definitely turned LLM-padded in the middle. And yeah, I think you're right about the actual science.

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