What exactly is 8-bit?

[TheMonsterAtlas]

I'm probably repeating something that has already been posted here but I'm not quite sure as to what exactly is defined as 8bit. I know Super Mario Bros. 3 and etc are 8bit, but why are they? I know those games are more than 1 byte of code. Does it have something to do with colors?

[Dusty]

I know Super Mario Bros. 3 and etc are 8bit, but why are they?

Because the NES was an 8-bit console. I'm pretty sure though the CPU was an 8-bit processor and it actually didn't really reflect graphics that much, if at all. But the 8-bit may refer to the overall palette of the machine, but I don't think NES had a 256(8-bit) color palette.

However I guess I'll leave it to the people around here who are more in-the-know about the technical side of these things.

[TheMonsterAtlas]

Yeah, I think it says the NES had like 48 colors and 6 grays @__@

[Kasumi]

I don't like 8-bit/16-bit used for describing graphics. People call Atari graphics 8-bit. People call NES graphics 8-bit. One is clearly very far ahead of the other. Bits per pixel is more descriptive as far as graphics go, but even that's not perfect.

I guess X-bit generally refers to the largest size number most of the CPU registers work with, but even that doesn't say a lot about how powerful a CPU is or what you can do with it. NES deals with 16bit addresses. There's nothing stopping it from working with 16 bit, or 24 bit numbers, higher bit numbers.

I don't think it's a very good descriptive term for much of anything the general public uses it for, but I guess a computer science major might have more to say about it.

[TheMonsterAtlas]

Well aparently what was stopping it from using so many colors was that the processor could only put a number of colors up on the screen at once. 25 for the NES to be specific. I can't really find any other information about the different 8-bit consoles.

[ptoing]

Doesn't the bit value of a processor have to do with the maximum amount of opcodes? Like an 8bit processor has a possible 256 opcodes at max. Something like that.

But yeah, even in graphics alone 8-bit is ambiguous. It could mean either Bitdepth, which in itself does not say much either, because it could be distributed in different ways, if the hardware was layed out like that. Or it could mean the amount of colours on the index.

Also a lot of systems use mixed bit ranges. The PC-Engine has an 8bit processor, but the graphics chip is 16bit.

[Ai]

Kasumi, that's mostly right. I guess the way to say it is that an N-bit cpu is designed to mostly manipulate N-bit values. Like you said you can handle bigger values but it's harder and slower (eg. manipulating 64-bit values on a 32-bit processor is slower than on a 64-bit processor)

Wikipedia says:

Eight-bit CPUs use an 8-bit data bus and can therefore access 8 bits of data in a single machine instruction. The address bus is typically a double octet wide (i.e. 16-bit), due to practical and economical considerations. This implies a direct address space of only 64 KB on most 8-bit processors.

@XLR8ED: Rendering is often done by a separate processor, so it's not easy to say 'Right, that's an 8-bit machine, so it can't have that many colors'. If you look at, for example, the MSX2, it had a 256-color mode, and the 2+ had HAM-like 19k/12k-color modes, plus sprites, but the CPU was just an 8bit Z80.
BTW, Wikipedia has a 'list of videogame consoles palettes' page which gives some of the info you want.

[9_6]

It probably means the same as for the 8-bit music kind: Looking/sounding like something from an old cosole..
I don't think it's oftenly used to accurately describe something on a technical level.

[PypeBros]

Doesn't the bit value of a processor have to do with the maximum amount of opcodes? Like an 8bit processor has a possible 256 opcodes at max. Something like that.

Not necessarily. 8-bit processor can perform computation natively only on 8-bit quantities. Your programmer is going to shout at you if you ask for a resolution higher than 256x256 because he'll need to find room for the 9th bit of some coordinates. If you really insist, he's likely to ask you whether that would hurt the game play if characters and ennemies never move by less than 2 pixels at once (he's planning to store x/2 internally already

These system typically had small memory, addressable in chunks of 256 bytes. That means the 6502 for instance (NES, C64 and many others) has only access to 2 pages of 256 bytes at once: the "special 0 page" and one page you select by setting its value in a special register.

Typical restrictions for such systems would be "no more than 256 tiles in your charset" and "you've got 8 bits to code your character attributes". That could be e.g. one background colour picked between 0-15 and one foreground color.

I don't think it would be possible to really describe 8-bit "exactly" when it comes to graphics or sound beyond the overall description that it is either "highly quantized" or "picking analog functions among a limited set and combining them". The 8-bit SID music sounds quite different from the NES music, for instance, but they share the fact that people used arpeggio when they needed chords because there was no proper way to create music with 3-tone-chords on systems that had merely 4 sound channels.

[ptoing]

Ah I see. C64 is not quite 6502, it's 6510, very similar tho. And the SID has only 3 channels even. I think the NES has 5, but on the NES each channel is fixed to a waveform and one is reserved for samples or something.

[PypeBros]

C64 is not quite 6502, it's 6510, very similar tho.

Standing corrected. I must have been mis-informed by mindbenders' promotional tape featured in my brother's tune

And the SID has only 3 channels even. I think the NES has 5, but on the NES each channel is fixed to a waveform and one is reserved for samples or something.

Yep, since they used special chips for sound and graphics, you'd have different limitations from system to system, but the basis is the same: you've got hardware capable of producing some limited waveforms, and only limited number of generators. Comparatively, a 16-bit machine has (much) more channels and is more capable of using arbitrary samples. Vocal samples are feasible on a 8-bit system, but they typically require nearly the full CPU power to be played, for instance.

[Hideon]

NES uses 16 colors simultaneously on the screen. If you see at games like Final Fantasy, 4 grayscale colors are almost permanent on the screen; two for interfaces and several things, black and white).
There are almost 4 colors for the charas, 2 for backgrounds and I think 2 more for objects or enemies.

Indeed, the GPU of NES is 4bits, not 8bits, ahd that has a lot to say on processing power. SNES had about 7 or 8 graphic modes, and each with variations in dimensions and more. GPU have some data processing capacity which is reflected in the screen resolution and color depth (in computing the resolution is for example 800x600x32, because that is the size in bits graphic data display buffer).

Consoles were 8-bit referring to the CPU. Similarly, PCM chips (music synthesizers) allowed values 8bits equally manageable with 8-bits, for consistency with the CPU and probably to facilitate data handling.
Also, the sprites are 8x8. If you remember (?), Most things used textures sizes equal to powers of 2 because it is easier or faster for the processor to handle such data.

PD.- My english sucks...

[ptoing]

NES uses 16 colors simultaneously on the screen.

The NES can have quite a few more colours on screen than 16.
(3x4)+1 for bg = 13 and 3x4 for sprites = 12 makes 25 colours at once, and this is without doing rastersplits.