Overclocking in theory..

[SF3D]

on a more relevant note one of my professors actually brought this stuff up in class asking if anyone had heard about the cpu being run under liquid helium. He was actually curious about how it ran at such a low temperature. Now i wish i had asked him more about it.

Cool! He was interested about "the Experience". You can tell him to contact us personally

Thanks Gautum and other guys about good info! I know this is exactly what Sampsa is looking for

[SNiiPE_DoGG]

I almost went there. I'm at BU computer systems engineering ...... EE is for girls

Haha too bad I suck at programming.... or I would still be CSE. thing is that I'm an extremely visual person and software and I don't always get along.

[GeorgeStorm]

Snipe, im with you there, programming just doesnt seem to work whenever i dot i!
This is great to hear though, I had heard that the lower temps allow greater frequencies at the same voltages (and I have hoped, considering the highest on air I have got with my e7300 is in my sig, and that took 1.7v!)
And so I was worried that there wasnt much point in using DICE with this cpu, (would be my first time)
However, reading stuff like this makes me realise that not only would I be able to use 1.8, 1.9 volts without it being too hot, due to the lack of heat, I will be able to get higher frequences at the volts I have already tried, (must admit, have tried 1.8v!)

George

[Sampsa]

I've always wondered if (excluding cold bugs) if there is not a best temperature at which to overclock a given processor at a given voltage. I know typically the colder the better but maybe there is a sweet spot, this may be something worth investigating with these AMD chips.

So far with Phenom II X4 it looks like the colder the better. We saw -242 Celsius measured from base of F1 EE copper container (1 - 2 mm from bottom surface):





and around -230 measured from AMD Pete Hardman's container where thermal sensor is milled right in the middle of bottom surface so it is basically touching CPU heatspreader. Under load temperature was -225 Celsius:



Since the system was running just fine at these temperatures I wouldn't be surprised if Phenom II X4 could work at -250 and -260C range. Next step is to design more sophisticated solution to use liquid helium to cool down the CPU to even lower temperatures than we achieved in Las Vegas.

[SNiiPE_DoGG]

Since the system was running just fine at these temperatures I wouldn't be surprised if Phenom II X4 could work at -250 and -260C range. Next step is to design more sophisticated solution to use liquid helium to cool down the CPU to even lower temperatures than we achieved in Las Vegas.

what do you think that would be? is it possible to set up a closed loop of pressurized liquid helium to make it colder?

[Sampsa]

what do you think that would be? is it possible to set up a closed loop of pressurized liquid helium to make it colder?

Yes or "double container" where is inner pot filled with liquid helium and some kind of lid adding pressure and outer pot filled with liquid nitrogen.

[Smartidiot89]

This explains a whole lot thanks! Always wondered why temperatues mattered so much when clocking, I only knew it did matter!

[Pedro Rocha]

Nice discussion , going to XOC Q&A section and sticky

[Gautam]

Tighter lattice due to shirnkage from the cold? Just simply lowers resistance, or what?

I suck at chemistry, hopefully someone else can pipe in with details at the molecular level. I only learned up to the equations.

[hey]

it seems you gave the answers, yes two main thing we have for overclocking,

1.increasing voltage

2.cooling down

1. is definetly for keeping 1-0 level when you increase clock frequency, and 2. is for higher electrical conductivity of semiconductors under cold which allows transistors to switch faster with lower potential difference.

but if we came to coldbug again, that is usually complicated,but here my theory on this is that;
yes, lower temp means higher electrical conductivity but that is the case for semiconductors only, if we look at metals or other materials side it is reverse, when you heat you got higher conductivity, so what i want to come with is that somehow metal molecular side of the chip may cause coldbug since its conductivy is effected by extreme cold. yea this is theory, some may prove or not by giving how the metal parts of chip acts

[GeorgeStorm]

Gautum,
How does th increase of voltage help reduce the high low delay, and therefore allow higher clockspeeds, is it just because more volts will cause the transistors to switch more quickly?

[Gautam]

There are two basic reasons why increased voltage lets the caps get charged faster and the transistors switch quicker. First of all, the increased supply voltage increases the drive current across the transistor, so it charges it's own output cap quicker.

Secondly, all voltages are increased, so the input voltage is increased as well. In my crappy diagram I idealized the input into a perfect square pulse, but in reality, the input is coming from another transistor's output itself, so the input also rises and falls for some given period of time, like below, so increasing the input voltage at the gate allows the transistor to start switching faster as well.

[cadaveca]

but is it really the voltage increase, or the current increase that allows faster switching?

Or is the voltage a sneaky way of bypassing current limits?

[K404]

Well higher voltage comes back to drive strength.

There are minimum setup and hold times for stable clock switching.

There are "on" and "off" thresholds for a clock signal. E.g.... 67% (or more) of max amplitude is "on" for the rising clock and 70% of max amplitude is "off" for the falling clock

Higher voltage to the clock gives it a higher maximum amplitude.

rising and falling edge clock transitions are not vertical lines with respect to time- they have a slight slope- a very steep one, but a slope all the same. They take a finite time to change

Making the max amplitude bigger but keeping the low-high transition time the same means that the signal will pass the "on" threshold faster and will be a more stable valid clock.


There is also a mean time to metastability which has a temperature dependence, as well as reliance on specific device constants. Metastability drawn as a clock means the signal meets itself coming back and cant decide if its on or off.....so falls over.
I should add some diagrams to show this but im too tired... if no-one beats me to it, I might give it a shot tomorrow.

[fiveprime]

It would be interesting to design a chip that would not compare on and off with set levels, but by the change from the previous step, this could possibly add more overclocking head room, although you would have to set the change threshold to a specific level because I would imagine that it would be unreliable after a point.

[Gautam]

but is it really the voltage increase, or the current increase that allows faster switching?

Or is the voltage a sneaky way of bypassing current limits?

As far as parasitic capacitances need charging, increasing one or the other while holding the other constant would make it happen quicker.

From the standpoint of the transistor, voltage in fact is at first directly proportional, and then a square factor for the drive current as it changes operation modes. You can check this out if you want, slides 5-8 are relevant.

[cadaveca]

Yeah, I understand that, I guess my question would be more directed at what point is it current, rather than voltage, that is needed, but then, I suppose that would depend on the resistance of the transistor. Cooling the cpu lowers the resistance, and by my mind, by better aligning the crystal's lattice, allowing for higher clocks at the same voltage.


Due to variations in the lattice structure, the current, and voltage, required for a specifc clock speed changes from chip to chip.



.

So who's go the transistors that require less current to run...AMD or Intel? Given AMD specs Phemon 940 .85-1.5v, I would think AMD...but I dunno, becuase the work they do is slightly different.

[fiveprime]

What if instead of a defined voltage for "on" and a defined voltage for "off, the switch would be based on the change in voltage between each cycle, this could possibly allow for "looser" cycles and improve clockability.

[Gautam]

That's known as sense amplification and is basically necessary in RAM to be practical.

[n30c0rt3x]

awesome Thread guys !!! Very nice explenations. This answer some questions that keep me awake @ night....

[Mr. Headshot]

Reducing temperature has different effects on the conductivity of different materials in the CPU. It will increase the conductivity of the copper and silicon, but decrease the conductivity of the silicon dioxide dielectric. The latter reduces current leakage and helps the system tolerate higher voltage.

[fl0w3n]

When will new semiconduter materials be required? In other words, are we at the boundaries yet of silicon? It seems as Guatam explained it, there will eventually be a limit of how fast the CMOS switches between PMOS and NMOS generating the 1-0 signal neccessary. Yet with AMD recently pushing past 7ghz on "old" technology, it seems like it is more in how effecient the rest of the system is and not neccessarily all on the switching of the signal inside the processor itself?

What did Intel pull off with SB that allowed the discharge of electron to happen quicker at "normal" operating temperature? I.E. 5ghz possible without increasing electron conductivity greatly through temperature?