GPU versus CPU clock speeds

[nitron]

I was just reading about current graphic cards on Anandtech. And then one question came to my mind: Why are current GPU clock speeds so much lower compared to current CPU clock speeds?

For example, the fastest processors from AMD are about 2.6GHz, from Intel nearly 4Ghz. Compared to that the chips from Ati or Nvidia have only 400-600MHz.

I had a course in Digital Circuit Design and I know that you can build slow and fast transistors and it's very much depending on the process technology you use. But I can't imagine that the process technology which Ati and Nvidia (or the foundries where their chips are produced) uses differs so much from that what AMD and Intel is using.

Another point could be power consumption, which depends very much on clock speed and on number of transistors. But the number of transistors of CPUs and GPUs is of the same magnitude.

Just some thoughts of mine and I would like to hear your thoughts! Maybe we can find an answer to that question.

later,
Ron

 

[PlasmaBomb]

Have a look here

http://www.sharkyextreme.com/forums_spotlight/38/4.shtml

or google it, this question has been asked a few times before.

All the best,
Chris 🙂

 

[Navid]

The highest Intel CPU external clock frequency is only 200MHz. The 4GHz that you are talking about is generated on chip. A phase-locked loop (PLL) is used on chip to multiply the 200MHz clock up to the intended frequency.

Now, you may ask why not have a PLL on the GPU?
A PLL is a complicated and expensive (Silicon area) block. It is possible. But, it may not be a reasonable business move to put a PLL on the GPU.

Does anyone know if there is any GPU out there with a PLL (clock frequency multiplier) on it?

 

[itachi]

Originally posted by: Navid
The highest Intel CPU external clock frequency is only 200MHz. The 4GHz that you are talking about is generated on chip. A phase-locked loop (PLL) is used on chip to multiply the 200MHz clock up to the intended frequency.

try 266, not 200.. and technically, the pll doesn't generate the higher clock from the 200 mhz clock, it generates the 200 mhz clock from the higher clock.

Now, you may ask why not have a PLL on the GPU?
A PLL is a complicated and expensive (Silicon area) block. It is possible. But, it may not be a reasonable business move to put a PLL on the GPU.

Does anyone know if there is any GPU out there with a PLL (clock frequency multiplier) on it?

plls have been used in video cards to display the output for a while now.

 

[Navid]

Originally posted by: itachi

Originally posted by: Navid
The highest Intel CPU external clock frequency is only 200MHz. The 4GHz that you are talking about is generated on chip. A phase-locked loop (PLL) is used on chip to multiply the 200MHz clock up to the intended frequency.

try 266, not 200.. and technically, the pll doesn't generate the higher clock from the 200 mhz clock, it generates the 200 mhz clock from the higher clock.

Now, you may ask why not have a PLL on the GPU?
A PLL is a complicated and expensive (Silicon area) block. It is possible. But, it may not be a reasonable business move to put a PLL on the GPU.

Does anyone know if there is any GPU out there with a PLL (clock frequency multiplier) on it?

plls have been used in video cards to display the output for a while now.

A PLL is a frequency multiplier when there is a frequency divider in the feedback path. A frequency divider can generate a 200MHz signal from a 2.8GHz signal. You do not need a PLL to do that.

A phase locked loop is a voltage controlled oscillator (VCO) whose phase is locked to the phase of a reference signal through negative feedback. Now, if you insert a frequency divider at the output of the VCO, the divided down frequency of the VCO will be locked to the reference hence the VCO frequency will be N times the frequency of the reference if the division ratio of the divider was N.

http://www.uoguelph.ca/~antoon/gadgets/pll/pll.html

Edit:
More PLL introduction links in case one is down.
http://members.tripod.com/~Malzev/radiodoc/pll.htm
http://en.wikipedia.org/wiki/Phase-locked_loop
http://www.minicircuits.com/appnote/vco15-10.pdf

This one is too detail. But, it is great for someone who is really interested.
http://www.national.com/appinfo/wireless/files/DeansBook_4_01.pdf

 

[Navid]

Originally posted by: itachi
technically, the pll doesn't generate the higher clock from the 200 mhz clock, it generates the 200 mhz clock from the higher clock.

No, you are mistaken.
Why would you need a PLL to divide a frequency? A simple digital counter can divide frequency. But, to multiply frequency, you will need a PLL.

 

[Navid]

Originally posted by: itachi
try 266, not 200..

Thanks for the correction.
Do you have any links? Or, do you mind telling me which Intel CPU has an external 266MHz clock?

I have a P4C 2.6G, which has a 200MHz external clock frequency. Of course, I can overclock it. But, I think you are talking about the default frequency being 266MHz.

Please kindly let me know.
Thanks,
Navid

 

[CrispyFried]

Originally posted by: Navid


Thanks for the correction.
Do you have any links? Or, do you mind telling me which Intel CPU has an external 266MHz clock?

This one?

 

[Navid]

Thank you.

 

[coomar]

so gpu's have no multiplier?