I think most people know the Nintendo NES was an 8-bit system. That tends to confuse people when it comes to the previous-generation system, the Atari 2600. Was Atari 2600 8 bit? Or something else?
The answer, of course, is that it depends.
The problem when defining game systems is that when you talk about bit count, sometimes people are talking about the graphics chip and sometimes they’re talking about the CPU. The two don’t have to match. The Sega Genesis boasted of its 16-bit graphics, but it could have claimed to have a 32-bit CPU without getting sued.
Was Atari 2600 8-bit? CPU-wise, almost
In the case of the CPU, internally the MOS 6507 CPU in the Atari 2600 was an 8-bit chip. But MOS Technology reduced the number of address lines to hit Atari’s target price of $12 in 1977. So while 8-bit CPUs can typically access 64K of memory at a time, the MOS 6507 could only address 8K at a time. So you can say the Atari 2600 was 8 bits internally but 5 bits externally. But the way Atari implemented it, the 6507 could only use half that memory, so Atari 2600 ROM cartridges were 4K in size.
So I guess you can say the Atari 2600 had a 4-bit implementation of a 5-bit implementation of an 8-bit CPU, if that makes any sense.
Why not implement all five bits?
Atari needed to dedicate memory to the game cartridge but also to the other two chips inside the console. Computers like the Commodore 64 implemented circuitry to overlay the I/O chips and memory and give you a way to switch between them. That would have cost more money, and Atari wanted the 2600 to cost $199. Atari didn’t completely waste that fifth bit. What they did made sense in 1977.
Was Atari 2600 8-bit? Not graphics-wise
The Atari 2600’s graphics chip was a bit of an odd duck. It could display up to 128 colors when connected to an NTSC television. That was rather advanced for 1977. That works out to 7-bit color. The Nintendo NES was limited to 54 colors, so in that regard it was a step backwards.
But the Atari 2600’s video chip didn’t have a frame buffer. A frame buffer is memory the system dedicates for graphics use.
The Atari 2600 literally didn’t have one bit of graphics memory. Instead, the Atari 2600 drew its graphics one line at a time, and the CPU spent more time redrawing the screen than it did doing anything else. That’s one reason why the Atari 2600 version of Pac Man flickers so much. And while the Atari 2600 had a ton of colors to choose from, it didn’t have a good way to display very many of them at a time.
All of this combined for a much simpler display than the computers and game consoles that followed it a few years later. Pac Man made the Atari 2600 struggle. Pac Man on most newer 8-bit systems could look almost exactly like the arcade version.
Why did Atari build such a half-baked 8-bit system?
This raises a question. If the Atari 2600 was 8-bit, why did Atari cripple it so badly? Cost. Atari designed the Atari 2600 to cost $199 at launch. Just the 8K of memory it would have taken to give the graphics chip a proper frame buffer would have cost over $200 in 1977. An Intel or Motorola 8-bit CPU of that time cost over $100, all alone.
Atari built what they could to meet that $199 launch price in 1977. Technology marched on, meaning the console had to compete with better and better systems with each passing year, which is why I argue with those who say the Atari 2600 was a disaster. And competitor Coleco obviously didn’t think so, otherwise they wouldn’t have cloned the Atari 2600 in 1982.
Yes, the Atari 2600 was outmoded by 1983 when interest in it tanked and it nearly took down Atari and the video game industry with it. But it wasn’t designed for 1983. It was designed for 1977 with the expectation it would have to hand the market off to its successor, which turned out to be the Atari 5200, sometime around 1981 or 1982.
That’s not to say Atari didn’t make mistakes. The original implementation of Pac Man could have been better. The later implementation of Ms Pac Man, which had better color and less flicker, proved it. But it’s unfair to call the hardware design a mistake. Had Atari built a costlier system, the 2600 might have been dead on arrival instead of selling 30 million units. In 1977, $199 was a lot of money, so asking for more would have limited the number of units sold.