The black bar to the left of the screen hid a major bug in the console and allowed programmers to push the Atari 2600 well beyond its intended capabilities

When the designers of the Atari 2600 gave the console only 128 bytes (not K, but bytes), they didn’t have enough memory to include one of the most basic elements of an arcade box: a frame buffer.

It forced programmers to redraw the entire screen every time something happened.

Unfortunately, that meant the game spent so much time just putting the image on the screen, there was little opportunity to do other things, like keep track of silly things like the score — or where you were on the screen. They were literally “racing the beam” of the television screen’s cathode ray guns.

If the game didn’t finish crunching numbers by the time the guns made it back to the visible part of the tube, black squares would garble up the far left of the screen. The programmers of Pitfall! simply left that part of the screen blank so they could put more CPU cycles into the snapping dragons, rolling logs, and deadly scorpions.

The original arcade Pac Man versus the Atari version. The CPU cycle black bar bug can be seen in the top left corner in the 2600 VCS version.

The other problem was the Atari 2600 could only keep track of so much: two players, two “missiles” and a “ball” — which was great in 1977 for games like Pong, but a real pain in the ass to program the hot game of the day: Pac Man. It’s one reason why the Atari version looked almost nothing like the 25¢ arcade game — the Atari couldn’t keep track of all the ghosts and dots eaten by the game’s round hero.

The other reason? Stupid accountants. The beancounters insisted the game be shipped with 2K of memory, not the 4K the programmer felt was necessary to make a respectable game. Pac Man turned out to be one of the biggest black marks on the Atari’s otherwise stellar reputation as a result.