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Experiments done, lessons learned.
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 Re: Experiments done, lessons learned.
Posted by Dred_furst on Mon Feb 21st at 1:43pm 2005

by track, i mean a wire on a circuit board (eletronics)

and i suppose all tracks are going to be less than 3.5cm on the processor as they are about 3.5cm big.

Thanks for doing the maths! thats added to my understanding explains other factors too
[addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by Rof on Mon Feb 21st at 4:04pm 2005

? quote:
The wavelength of light has no bearing on it's velocity.


This is only true in free space. Once you have waves propagating in a medium, like light in glass, or RF signals through copper, you get an effect called dispersion; different wavelengths (frequencies) of the signal travel at different speeds.

For example, blue light is slower than red light when it's travelling through most transparent media. That's why a prism splits up light into different colours.

Now if you have a very brief pulse, it requires lots of bandwidth, i.e. a wide range of signal frequencies which add together to make up the pulse shape. If the bandwidth is broad enough, the different frequency components travel at different speeds, and the shape of the pulse gets distorted. Travel too far along and the pulse gets smeared-out.

Imagine a 0 and a 1 travelling down a wire. If the dispersion is too high, the 1 gets broader and broader until it overlaps the 0. At the other end of the wire, there's no way to tell which was the 1 and which was the 0.


[addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by Leperous on Mon Feb 21st at 4:15pm 2005

Plus electricity doesn't travel at the speed of light. I believe the electromotive thingummyjigger does, but the electrons themselves can't.



Quote
 Re: Experiments done, lessons learned.
Posted by keved on Mon Feb 21st at 4:42pm 2005

? quoting willow
It's funny, that no one mentioned the whole problem with these "tests" is one chips is a celeron while other is a P4.

Yeah. I've got 2 PCs...one a Celeron 2.4, the other a P4 2.4. Otherwise, the bits inside are identical. I run the P4 in dx9 mode and get roughly the same FPS as the Celeron which is in dx8 mode. I appreciate that software, XP setup, etc may have a bearing but that's quite a marked difference.





Quote
 Re: Experiments done, lessons learned.
Posted by fraggard on Mon Feb 21st at 4:43pm 2005

? quote:
Plus electricity doesn't travel at the speed of light. I believe the electromotive thingummyjigger does, but the electrons themselves can't.

Force?

And besides, processor speeds are not even close to being limited by the speed of light. Methinks dred_furst isn't very clear about the topics he's talking about.

We are nowhere near close the theoretical limitations of the current architectures. TB is dead on when he says heat dissipation is a bigger issue. That, and also the fact that semiconductors do not behave too predictably at the frequencies we have reached.

Edit: Semiconductor junctions, to be more accurate.

More edits:
? quote:
yeah Celerons are basically P4's that were rejects and are missing some math instruction sets.


Jinx, you have any links explaining this some more? AFAIK the instruction sets supported by P4 williamette, P4 Northwood and the celeron are identical (MMX, SSE, SSE2). And they can most definitely not be missing any of the core instructions or the built in arithmetic co-proc instructions. That's just silly.

Some more edits:
Willamette, Northwood (improved 0.13micron version.), Celeron (Willamette core, only difference is L2 cache). Most detailed reference I could find.




Quote
 Re: Experiments done, lessons learned.
Posted by Dred_furst on Mon Feb 21st at 4:51pm 2005

? quote:

? quote:
Plus electricity doesn't travel at the speed of light. I believe the electromotive thingummyjigger does, but the electrons themselves can't.

Force?

And besides, processor speeds are not even close to being limited by the speed of light. Methinks dred_furst isn't very clear about the topics he's talking about.

We are nowhere near close the theoretical limitations of the current architectures. TB is dead on when he says heat dissipation is a bigger issue. That, and also the fact that semiconductors do not behave too predictably at the frequencies we have reached.

Edit: Semiconductor junctions, to be more accurate.


I must admit i tried to explain something that my dad explained to me, that could be false anyway, so i could well be talking rubbish anything I say (oh wait, im going round in circles, time for me to shut up)

back on with something that isnt high-level physics:
Yes, i guess P4's are faster that Celerons.
[addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by lucas_maximus on Wed Feb 23rd at 2:11am 2005

? quote:
the wavelength of light is "reduced" when the hz of the changes size. elecricity travels at the speed of light, and so has the same maximum speed. the length/width of the current ATX boards are equal to this "reduced" wavelength. therefore any higher frequency means the same track can have both a 1 and a 0 on the same track.

Happy understanding!


electricity doesn't travel at the speed of light, only the effect of electricity is instantaneous. electrons in a wire only travel a few centimetres in an hour through a wire.




Quote
 Re: Experiments done, lessons learned.
Posted by Tracer Bullet on Wed Feb 23rd at 3:10am 2005

? quoting Leperous
Plus electricity doesn't travel at the speed of light. I believe the electromotive thingummyjigger does, but the electrons themselves can't.

Electric SIGNALS travel at the speed of light. Not electrons. It's like turning on a faucet. The water comes out immediately, but that does not mean the water traveled all the way from the well in that fraction of a second.

posted by Rof


Now if you have a very brief pulse, it requires lots of bandwidth, i.e. a wide range of signal frequencies which add together to make up the pulse shape. If the bandwidth is broad enough, the different frequency components travel at different speeds, and the shape of the pulse gets distorted. Travel too far along and the pulse gets smeared-out.

Imagine a 0 and a 1 travelling down a wire. If the dispersion is too high, the 1 gets broader and broader until it overlaps the 0. At the other end of the wire, there's no way to tell which was the 1 and which was the 0.

That is an interesting implication of the uncertainty principle I had never considered, but does it apply to electric signals? It seems more applicable to optical computing or fiber-optics. Surely even modern electronics can be treated classicaly. I kind of doubt they could have continued to build faster computers as quickly as they have if quantum effects such as this were becoming prominant.

[addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by Rof on Wed Feb 23rd at 4:07am 2005

At high enough frequencies (>100 MHz or so), electrical signals can be usefully thought of as electromagnetic waves travelling down a waveguide (the wire). In fact, you can even treat simple DC circuits like that if you want to, though there's no point in doing so.

Dispersion is a classical effect, and it and the idea of short-duration signals requiring a wide bandwidth works for any wave (water waves, sound waves, light waves, radio waves, etc.). However, it is indeed related to the uncertainty principle, when you get down to it.


[addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by fraggard on Wed Feb 23rd at 4:57am 2005

? quote:

? quote:
The wavelength of light has no bearing on it's velocity.


This is only true in free space. Once you have waves propagating in a medium, like light in glass, or RF signals through copper, you get an effect called dispersion; different wavelengths (frequencies) of the signal travel at different speeds.

For example, blue light is slower than red light when it's travelling through most transparent media. That's why a prism splits up light into different colours.

Now if you have a very brief pulse, it requires lots of bandwidth, i.e. a wide range of signal frequencies which add together to make up the pulse shape. If the bandwidth is broad enough, the different frequency components travel at different speeds, and the shape of the pulse gets distorted. Travel too far along and the pulse gets smeared-out.

Imagine a 0 and a 1 travelling down a wire. If the dispersion is too high, the 1 gets broader and broader until it overlaps the 0. At the other end of the wire, there's no way to tell which was the 1 and which was the 0.



The underlined word: Do you mean distortion?

Dispersion seems to indicate an even spreading out of different frequencies. This is, in general, untrue for any communication medium using electrical signals. I don't think it is possible to predict, accurately, how much a signal of a given frequency will be distorted (phase-shifted, attenuated, etc).

I thought dispersion was only an issue in optical media.




Quote
 Re: Experiments done, lessons learned.
Posted by Rof on Wed Feb 23rd at 5:10am 2005

Nope, I mean dispersion. At high enough frequencies, it becomes an issue for electrical signals, too. I'm not sure it's the limiting factor in the case of CPUs, but it will be an issue for ~>1 GHz signals.

I used to do research on high-frequency modulators for optical telecoms; not only did we have to worry about optical dispersion in the fibre, but also dispersion of the electrical signals driving the modulator. Co-ax cable suitable for 20GHz signals is a right pain to use, it's more like plumbing than anything.
[addsig]



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 Re: Experiments done, lessons learned.
Posted by Tracer Bullet on Wed Feb 23rd at 6:09am 2005

Cool. I'm always happy to learn something new. I really wish I had been able to take a waves and optics class while I was in school. I know more about quantum mechanics (which isn't very much) than classical waves, although I suppose there are many parallels as this topic points out. [addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by Orpheus on Wed Feb 23rd at 11:13am 2005

never fails, you guys do this to my threads every time

just once, i would like to be able to follow it from beginning to end. actually, the only time i see the end of a thread and be sure i fully comprehend its contents is when lep locks it after my first post.

you kids are way to smart to associate with dumb people like me. :/

[addsig]



Quote
 Re: Experiments done, lessons learned.
Posted by fraggard on Wed Feb 23rd at 11:53am 2005

? quote:
Nope, I mean dispersion. At high enough frequencies, it becomes an issue for electrical signals, too. I'm not sure it's the limiting factor in the case of CPUs, but it will be an issue for ~>1 GHz signals.


Something new each day I hadn't heard that term applied to electrical signals in my course work before. A bit of googling tells me that delay distortion is also called dispersion, so I was wrong.




Quote
 Re: Experiments done, lessons learned.
Posted by Gwil on Wed Feb 23rd at 12:57pm 2005

? quote:
never fails, you guys do this to my threads every time
just once, i would like to be able to follow it from beginning to end. actually, the only time i see the end of a thread and be sure i fully comprehend its contents is when lep locks it after my first post.
you kids are way to smart to associate with dumb people like me. :/


Don't worry Orph, when the Snarkpit Science Club start it sends me running for cover too I'm going to go and have a game of marbles if you fancy it [addsig]




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