The Atari 2600 was an extremely popular yet very simple game console back in the 1970s. They sold, apparently, over 30 million of them, and, of course, these things broke. We’d get calls from friends and — remember, back then normal people weren’t computer savvy — nine times out of ten, we’d ask them to swap the controllers to show them it was a bad controller, and problem solved. But if you did have to open one up, it was surprising how little there was inside, as [Steve] notes in his recent teardown.
The bulk of the circuit board was switches, the power supply, and a TV modulator if you remember those. The circuit board was a tiny thing with a shrunk-down 6502, a 6532 RIOT chip, and a custom chip called a TIA. If you are familiar with those chips, you might wonder if the TIA had any memory in it. It didn’t. Nearly all the ROM and RAM for the game lived in the cartridge itself. Sure, the RIOT has 128 bytes of memory, but that’s not much.
The TIA generates timing signals using an odd configuration that [Steve] discusses. The limited memory explains some things you may or may not have noticed. Most games have a symmetrical background where the left is a mirror copy of the right. The TIA architecture explains why. You could modify things, but you had to do it between scan lines which left a scant 76 clock cycles to do whatever you needed.
There are a lot of tricks for squeezing the most out of the limited architecture that [Steve] highlights. He also provides links for writing your own games and running them on real hardware or an emulator. Since the box was popular and had a — sort of — 6502 inside, you’d think someone would have turned it into a full computer. Someone did.