If you were, for example, iterating over a column of a 2D array with a stride equal to some power of two, you'd end up hitting the same IC repeatedly. This limits your bandwidth to that of a single IC, rather than balancing it over all of them. (I'm simplifying a little, but that's the gist)

So they try to "swizzle" things, using a formula like the one in the article.

On 80's arcade games and home computers you can try piggybacking a known working RAM chip onto each of the RAMs for a quick diagnosis, if you're lucky (it doesn't always work).

Then all you'd need is an infrared imager.

For HW hackers playing master it is ok. But for the average person it is not an option.

You can't change your RAM and this is disastrous.

Even normal computer shops may torture you for weeks (after you have been torured by the mother board)