2 16-bit CPUs vs 1 32-bit CPUs

[dragonboy]

I've heard in many many threads "If the Neo Geo was 24-bit, then the Sega32xCD would be a 32+32+16+8+16=104-bit system," but I'm curious what exactly is the proformance difference between having one CPU with a bit depth of x and many CPUs with bit depths adding up to x? and why?

[evildragon]

Far from it.. At best with everything, the Genesis could be a 32-bit system, if it had the 32X.

Those bits don't magically "add up"..

PS: Technically having more bits doesn't make a CPU faster. That's what I was told. Besides, it takes up more RAM anyway, because the data is longer.

[MN12BIRD]

Hell my "32bit" CPU in my computer is playing Call of Duty 4 in max settings!

[evildragon]

I have a Pentium 4 CPU in my system, it's the Prescott 2M core, which is 64-bits..

[dragonboy]

PS: Technically having more bits doesn't make a CPU faster. That's what I was told. Besides, it takes up more RAM anyway, because the data is longer.

That's what I always thought. If increasing bit depth doesn't increase the speed, why do people get impressed by the usage of a 32-bit CPU, but think using 2 16-bit CPUs is a ripoff because the bit depth is still 16-bit? Wouldn't the usage of 2 16-bit CPUs be more powerful than 1 32-bit CPU because you have more processors?

[MN12BIRD]

Programming games for multiple CPU's is much harder and never %100 efficient either. One fast CPU would be better than two half speed CPUs but I don't think we are talking about half speed CPUs here. But if you had two similar CPUs one with 16 bit registers and one 32 bit would the 32 bit CPU not be capable of more advanced code that if written for properly would in its own way make it faster??

[Tanegashima]

Man, this reminds me of all that Jaguar hype about 32 + 32= 64 bits...but that thing looked bad for a 32 Bit system (3-D wise at least). But if you use Atari's reasoning, that would make the Sega Saturn a 64 bit system because it had two 32 bit processors right?

[Joe Redifer]

Using Atari's math, the Saturn would be at least 80 bits. I think the number EGM came up with was "104-bit monster" by adding all of the Saturn's processors together Atari-style.

[tomaitheous]

There are sooo many factors when trying to compare one CPU type/style to another, but it's even more complicated when comparing two processors against another whole different processor.

People hype 32bit processors because this was about the turning point where MIPS and performance really started going up. It's not just the 32bit factor, but more of a marker in the processor time line. 32bit usually require more memory in the fact that instructions and data access are done in 32bit segments. But I won't go into extreme detail.

Getting maximum performance from two processors isn't always possible and many times you'll have some sort of overhead that makes the process less efficient than what you'd think. There are specific situations where two processor might be better than a single at twice the speed, but it's pretty rare and very specific. Usually the second processor is spending a lot of time waiting because the code on both processors need to synchronize and vice-versa.

For example, you'd have the second processor preform a specific task like collision detection and then once it's done - wait for the main processor to give it another command (usually in the form of flags or a subroutine call). Since a routine doesn't always execute at the same speed every time, the main processor might be waiting for the co-processor at a times or the co-processor has finished and is waiting for the main processor.

So unless it's something that would be difficult or faster to split up to another processor, the overhead isn't worth the cost. And the performance isn't doubled. Having a processor running at twice the speed as opposed to a dual processor setup, means you could effectively optimize for 100% of the single CPU resource, but not so with a dual setup.

I should note that the Hitachi's SH series are pretty fast in instruction cycle times. Much faster than the 68k even if it were running at the same speed/mhz. So are a lot of 32bit processors.


Man, this reminds me of all that Jaguar hype about 32 + 32= 64 bits...but that thing looked bad for a 32 Bit system (3-D wise at least). But if you use Atari's reasoning, that would make the Sega Saturn a 64 bit system because it had two 32 bit processors right?

The Jaguar had several CPUs and I believe two of them had 64bit registers. I'm not sure of the ALU was 64bit or not.

[TmEE]

I love MDs dual CPU nature... both CPUs run pretty much independently and thus I can dedicate both to different tasks (in my case, Z80 does all sound stuff and 68K all game).

[lilmul123]

Bits don't even matter. The Intellivision was the first "16-bit" system but you wouldn't know it basing it on the SNES or Genesis. Also, modern computers are capable of running 16/32/64-bit code. The difference between 16-bit and 32-bit is huge but there is little to no difference between 32 and 64-bit. (If you're a computer nerd, think about it like this. Windows 3.11 was the last 16-bit Windows OS and 95/98/Me/XP/Vista are all 32-bit versions. XP and Vista come in 64-bit, but they're the same damn thing as their 32-bit counterparts. Really, 32-bit processors are no more powerful than processors that can process 64-bit+. Only real difference is that they can access more than 4 gigs of memory)

[TmEE]

4gigs is only limited to address bus size... 68000 is 16bit but it doesn't limit its address space to 64KB...

[tomaitheous]

Really, 32-bit processors are no more powerful than processors that can process 64-bit+. Only real difference is that they can access more than 4 gigs of memory)

The problem is that the 64bit processors has *other* performance increases/upgrades than just 64bits. One of them, if you're comparing for x86, is that 32bit processors still only have 4 general purpose registers (and they are not *true* general purpose regs), AMD's 64bit version adds additional registers. I'm not sure of intel's 64bit cpu increases in the amount of registers.

[twoquickcapri]

The Jaguar had several CPUs and I believe two of them had 64bit registers. I'm not sure of the ALU was 64bit or not.

Yes the Atari Jaguar had a 64 bit Object Processor and Blitter built into the GPU "Tom" Processor. Also the ram was on a 64 bit bus.

[dragonboy]

The problem is that the 64bit processors has *other* performance increases/upgrades than just 64bits. One of them, if you're comparing for x86, is that 32bit processors still only have 4 general purpose registers (and they are not *true* general purpose regs), AMD's 64bit version adds additional registers. I'm not sure of intel's 64bit cpu increases in the amount of registers.

what?? only 4 registers? Motorola 68000 had 16 registers and it was only 16-bit?

I alway expected 32-bit CPUs to have around 64 or 128 registers since the instruction legnth is longer and they could fit more register-select bits in 32-bit instructions than on 16-bit instructions.

[tomaitheous]

what?? only 4 registers? Motorola 68000 had 16 registers and it was only 16-bit?

I alway expected 32-bit CPUs to have around 64 or 128 registers since the instruction legnth is longer and they could fit more register-select bits in 32-bit instructions than on 16-bit instructions.

You'd think. Register to register operations are faster than memory or cache to register, etc. But backwards compatibility added to the problem. Instead over time they created bigger cache levels, larger pipelines, specialized parallel processing for pair/multiple instructions, etc.

Other brand 32bit CPUs have much larger set of registers like Hitachi, MIPs, NEC, ARM.

[lilmul123]

4gigs is only limited to address bus size... 68000 is 16bit but it doesn't limit its address space to 64KB...

Hence why PCs take advantage of PAE which increases addressable space to 36-bits instead of 32.

[Psy]

I love MDs dual CPU nature... both CPUs run pretty much independently and thus I can dedicate both to different tasks (in my case, Z80 does all sound stuff and 68K all game).
Yes, having a processor dedicated to audio gives a huge bust in performance as the main game code just tells the Z-80 when it has to play a sound effect or change the music. The same is true for graphics which why at the heart of modern 3D chips are fast processors dedicated to 3D.

Sony does think more processors the better thus the design of the PS3 and when running *nix builds optimized for the PS3 has insane amount of MIPS. The PS3 is the ultimate *nix box, though I don't think that is what Sony was aiming for with the PS3.

[tomaitheous]

Yes, having a processor dedicated to audio gives a huge bust in performance as the main game code just tells the Z-80 when it has to play a sound effect or change the music. The same is true for graphics which why at the heart of modern 3D chips are fast processors dedicated to 3D.


For samples playback yes, but for FM and PSG control no (that's only 1-3% cpu resource per frame). But that's only because the Genesis lacks any real interrupt mechanism to playback samples via the 68k on a realistic level. Meh- the 68k is slow at interrupts anyway (50cycle overhead), so I guess I'd still have the z80 playback to the DAC regardless :D

[TmEE]

Having a complex Vint routine has pretty nice speed impact from my tests... especially on 60Hz machines. I'll be having hard time getting my 50Hz optimized game running decently on 60Hz (MD game)...

[dragonboy]

I love MDs dual CPU nature... both CPUs run pretty much independently and thus I can dedicate both to different tasks (in my case, Z80 does all sound stuff and 68K all game).

You always say you make a lot of cool music for the Sega Genesis, but whenever I click on the links to your music, it doesn't work on my computer. What do I need on my computer to hear your music?

(I already have an emulator, just so you know)

[evildragon]

WinAmp for one. Anything that plays OGG.

I think VLC does too.

[TmEE]

the ROMs SHOULD work in emulators, they do on real HW, and if they don't start, the emulator used sucks.

[Joe Redifer]

Even if they do run, the emulator may still suck and not produce the sounds correctly.

[TmEE]

Fusion does sound very good, and Gens and other emus I've tried are acceptable until drums come to action... Emulators I've tested and found to work : Fusion, Gens based ones, Kgen98, Genecyst, Megasis, Retrodrive, Regen, DrMD(on GP32), Xega and Dgen.

[dragonboy]

Fusion does sound very good, and Gens and other emus I've tried are acceptable until drums come to action... Emulators I've tested and found to work : Fusion, Gens based ones, Kgen98, Genecyst, Megasis, Retrodrive, Regen, DrMD(on GP32), Xega and Dgen.


I have Gens, but it doesn't work on mine. Is there something special I have to do while downloading it?

[TmEE]

not that I know of...