What makes a PPU better than a CPU?

A

Akutsukun

Weaksauce
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How can something like that be so much better than a CPU at doing calculations and such for physics? Aren't CPUs a lot faster, more powerful and such?
 
It's all about dedicated vs. general

Any microprocessor designed to do a specific task will always be faster than a processor designed to do a whole lot of different things and then adapted to do the same specific task. You could ask the same question between a GPU and a CPU.
 
The PPU is designed to be crazy fast at floating point math. The cpu has to balance it's capabilities between several things.
 
A CPU is a jack of all trades general purpose machine. Sure it can do calculations and such, and has a fast clock speed. However a PPU is basically a big huge mammoth giant calculator. It does one thing and it does one thing well and that is perform the necessary calculations for physics. They dont have to waste transistors for all the crap that is needed to make a general purpose CPU.
 
CPU is doing the blonde, redhead, and the asian girl at the same time.
The PPU shows up and takes the blonde so the CPU can focus on the other 2 girls!
 
Majin said:
CPU is doing the blonde, redhead, and the asian girl at the same time.
The PPU shows up and takes the blonde so the CPU can focus on the other 2 girls!
Click to expand...

Nice analogy! :D
 
Erasmus354 said:
A CPU is a jack of all trades general purpose machine. Sure it can do calculations and such, and has a fast clock speed. However a PPU is basically a big huge mammoth giant calculator. It does one thing and it does one thing well and that is perform the necessary calculations for physics. They dont have to waste transistors for all the crap that is needed to make a general purpose CPU.
Click to expand...


CPU's rely incredibly heavily on FP calculations. Since I've yet to run into a game whose physics caused my computer to slow down(except for the demo *designed* to do just that, in order to convince me I need one of their cards), I wonder how long it will take before cpu speeds are high enough that they can handle the additional physics load of the manner of the aegia demo/games. I might buy one for $100, no higher.
 
Spewn said:
...Since I've yet to run into a game whose physics caused my computer to slow down except for the demo *designed* to do just that...
Click to expand...

A fair point, yet slightly flawed - it's akin to saying that you don't really notice the difference between driving your car or a ferrari on a 50mph road, but when it's on a racetrack there's a lot of difference.

A more accurate way of expressing your sentiment is that because past games have been designed with CPU limitations in mind you've never noticed the *lack* of physics.

If the speed limit wasn't there you'd sure as hell want to get a ferrari. :D
 
Majin said:
CPU is doing the blonde, redhead, and the asian girl at the same time.
The PPU shows up and takes the blonde so the CPU can focus on the other 2 girls!
Click to expand...
I like the way you think. :D
 
Spewn said:
CPU's rely incredibly heavily on FP calculations. Since I've yet to run into a game whose physics caused my computer to slow down(except for the demo *designed* to do just that, in order to convince me I need one of their cards), I wonder how long it will take before cpu speeds are high enough that they can handle the additional physics load of the manner of the aegia demo/games. I might buy one for $100, no higher.
Click to expand...

There used to be no GPU's, and 2D speed was king. (look up the TsengLabs ET6000, the fastest 2D only card made)

But then someone (3dFX) decided to make a 3D add in card, there was only one game that could use it, and even that was only with a software patch. (GLQuake, Quake was software rendered before the GLQuake Patch)

Now do we wonder if GPU's are needed?

==>Lazn
 
if u want a similar comparison.. take 3dmark05 see what ur gpu does in fps and then see what ur cpu does

you will prob go from 60fps to 3fps

it has one purpose and it does it well, i can only assume the same for ppu
 
Seems the Math Co-Processor is being resurected with a new name (PPU).

Those of us that built PC's in the 80's prolly remember the old Math Co-Processor which was used for floating point calculations.

-LW
 
LazerWire said:
Seems the Math Co-Processor is being resurected with a new name (PPU).

Those of us that built PC's in the 80's prolly remember the old Math Co-Processor which was used for floating point calculations.

-LW
Click to expand...

CPU's still have a math coprocessor (x87), and even a vector coprocessor (MMX,SSE, etc). They are just integrated now.

But the PPU is a step beyond and dedicated to streaming physics.. I assume still vector math, but I could be wrong.

==>Lazn
 
Majin said:
CPU is doing the blonde, redhead, and the asian girl at the same time.
The PPU shows up and takes the blonde so the CPU can focus on the other 2 girls!
Click to expand...

Actually it's more like GPU is doing the blonde :eek: while CPU is in the living room flirting with the brunette, redhead, and asian. CPU's keeping them entertained, but otherwise not getting very far. Then the new roommate, PPU, gets home and he's exactly the asians type so next thing you know the PPU and the asian are doing it in the PPU's room :D while CPU is still in the living room with the brunette and redhead. However, now without the asian to distract him CPU is getting some "accidental" bodily contact and even the occasional kiss on the cheek from the brunette and redhead. Unfortunately though he will NEVER go all the way with either of them because he just doesn't have that kinda play. :(
 
Digital Viper-X- said:
what will happen to PPU cards when quad core cpus come out? and 8 core cpus?
Click to expand...

We will have 8 cores with a PPU. According to ATi, their GPU is 37 times faster than a high end CPU at rendering physics.

A general purpose CPU can only run a limited number of instructions at once, because general code is not parallel. A CPUs life is spent trying to run a single thread as quickly as possible through out of order execution.

Graphics and physics code, however, is highly parallel. So, you can take a ton of simple processors and add them together to make a very fast processor capable of running dozens of graphics/physics calculations at once.
 
Digital Viper-X- said:
what will happen to PPU cards when quad core cpus come out? and 8 core cpus?
Click to expand...

Admittedly these numbers are bit old, and biased, but Ageia says current hardware and software can handle roughly 200 objects while their hardware with proper software can handle about 32,000 objects.

Assuming (generously) they mean 200 objects with a single CPU and just 10% of the processor dedicated to physics then we should be able to estimate an 8 processor situation...

Assuming 7 processors would be used for physics, the other one for everything else we get 7*200 = 1400 objects.
Then (again generously) assuming each processor would effectively be at 80% efficiency (you always lose power when sharing between multiple CPU's), we get 1400*8 = 11,200 objects.

So being reasonably generous to the CPU's, a single 8 core CPU would only get us to about 1/3rd the physics processing power of a single PPU.

And that's all assuming someone bothers to program for multi-processor physics, which would be pointless with PPU's available.
 
VVVVVVVVVVVVVVVI said:
A general purpose CPU can only run a limited number of instructions at once, because general code is not parallel. Its life is spent trying to run a single thread as quickly as possible through out of order execution.
Click to expand...
Well, that's part of what adding multiple cores is doing, allowing programmers to parallelize their code. The problem is that is a difficult task.
I had to work on the Drinking Philosophers problem for my Operating Systems class, using posix threads. Getting it functional was a difficult task for most of the class, and I don't know if any one reached the higher quality solutions (most used a big lock when grabbing philosophers resources, rather then breaking them down into groups). This was an undergraduate class by the way, most of the students didn't have that much experience (for many this was their first time actually using threads at all).

arentol said:
And that's all assuming someone bothers to program for multi-processor physics, which would be pointless with PPU's available.
Click to expand...
Ageias own PhysX SDK is multithreaded (at least its supposed to be), so it can use the other cores/processors if you don't have the hardware acceleration.
 
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