Note that the error rate is not proportional to the amount of RAM, it is proportional to the physical volume of the ram chips. (The primary mechanism that causes errors are highly energetic particles hitting the chips, the chance that this happens is proportional to the volume of the chips.) This means that the error rate per bit goes down as density goes up.

Cosmic rays causing the errors has got me thinking about if the error rates vary with the time.

Do you get more/less errors when it's day time (due to the Sun)? Does the season affect it (axial tilt means you're more/less "in view" of the galactic core)?

Wouldn't it go up if the density increases? If the particle hits the chip there are more bits at the place where the particle hits.

So while the chance of hit is lower (per GB), if it hits its effect will be higher (more bits flipped).

It is an interesting question but I think the parent poster did not mean density in the pure physical sense.

That is more memory but less mass which is not physical density. Also I am not sure if gamma rays need to just hit the physical bits to mess things up. If is the case where other things can be hit then it seems surface area might have high correlation but probably not.

I don't know what the answer is but I would imagine that the error rate would be the same percentage assuming orientation is kept the same.

Of course if you are going at extreme macro sense (think Asimov last question computers [1]) then density absolutely probably plays role as gravity starts to cause enormous amount of collisions. This actually happens in stars and is why photons take a long time to escape from the star as well as the edge of black holes where collisions are happening extremely frequently.

[1]: http://multivax.com/last_question.html

An alpha particle for instance is atleast an order of magnitude smaller than smallest transistor. The maximum damage it can do is effectively 1 bit.

Alpha particle won't penetrate that far, it will be stopped at the building level, or at the enclosure. Piece of paper blocks it.

Beta and gamma are the ones that can do damage (not sure about beta), and gamma can pass through the entire chip, so it can hit multiple transistors, depends on the angle and the way they are located.

Actually these high energy particles tend to be order of size of proton or less - so make that 6 orders of magnitude smaller than smallest transistor.