NES flickering and hardware wierdness

[Falco Girgis]

As you may know, this weekend I've gotten in touch with my roots. I've just had one NES marathon after another.

I'm curious. I began to notice patterns in the seemingly random flickering that the NES featured. When lots of things are onscreen, the flickering gets worse.

I looked it up online, and all that I found out is that when four or more sprites are drawn onscreen at the same time it happens. What's up with that?

Also, have you ever played Super Mario bros. 3 for the NES? Those graphics are great, but the right side of the screen is always warped. It changes colors randomly and stuff as tiles appear.

Now on the other hand, Super Mario bros. 1 (one of the more primitive NES games) runs super smooth and has no screen distortion. WTF is up with that?

Also, I'm sure every owner of a non-toploading NES console has seen this. When your cartridge gets dirty, things might get jarled as you play. Tiles might be switched and your 89 coins might become something like 19dDlf coins. What does this mean? What causes that? I know it has to do with not being able to read the cartridge, but what causes the replacement with letters and such and what do they mean?