It turns out that, back in the early '80's, with the vast increase in demand for DRAM that was forced by the rapidly growing PC market, they discovered that ceramic packages made from material, most of which actually came from a local ceramic mfg, contained traces of radioactive elements, since it came from western Colorado and eastern Utah, where such materials are much more common than, say, in Maine.

The Japanese mfg's found that they could remedy the general soft error problem pretty easily by XORing a couple of the address lines with the data, thereby reducing the general tendency of alpha particles to be attracted to portions of the memory array that were at zero while being repelled by those that were at a one state.

Unfortunately, it didn't help with the slightly higher than nominal radioactivity of ceramics made from raw material from eastern Utah, and western Colorado. People used to mine uranium from there, doncha know!

RE