4 ms·

Did you use "lucky" here sarcastically, or do you actually need to be lucky with binning to be able to undervolt without issues? (I thought that was a concern w

Did you use "lucky" here sarcastically, or do you actually need to be lucky with binning to be able to undervolt without issues? (I thought that was a concern with overclocking?)

londons_explore 6y ago
The same issues occur with both.
jchw 6y ago
Undervolting goes hand in hand with overclocking. The goal is higher clocks. The enemies are stability and heat. Undervolting reduces heat but the impact on stability depends on the silicon lottery. For mobile chipsets, undervolting at the same clocks is a nice performance uplift because of the reduced heat (on a system that undoubtedly does not have the best heat dissipation.) Overvolting is also useful for overclocking; at a point it can help increase stability. But generally I think you want to hit a point at which you are getting the highest clocks with the lowest voltage that is still stable.
- mehrdadn 6y ago
  Thanks!
magicalhippo 6y ago
Roughly, the transistors in a chip can have more or less internal resistance (Rds) due to impurities and variations during production. There's no way to know from one chip to the next until you try them. If it has less internal resistance it will generate less heat for the same amount of work. Semiconductors are constrained by the maximum junction temperature[1], and CMOS logic chips like modern processors primarily consume power when switching. So there's a thermal limit to how fast they can switch. Thus having lower internal resistance can allow you to clock higher (switch more often) before reaching the thermal limit. However, when switching they act as varying resistors, and the amount of power dissipated in any resistor depends on the square of the applied voltage (P = V^2/R). So if you can run your chip on a lower voltage, it will dissipate a lot less energy when switching, thus allowing you to switch faster before being thermally limited. When overclocking, you ask the transistors to switch faster. To turn a MOSFET[3] transistor on or off, you need to transfer a certain amount of charge (aka electrons) into or out of the gate. The faster you can transfer the charge (more electrons per second ie the higher the current) the quicker the transistor turns on. And the way to do that is to increase the voltage[2]. So overclockers tend to bump up the voltage when going for the super-high clocks. But as you see from above that causes a massive increase in heat, thus requiring significantly more cooling. I'm no semiconductor expert though, so I might got some of this wrong, but I hope I got the essence right. Also I'm not sure if the impurities and such that lead to the variability of the internal resistance is related to the ones affecting the ability to undervolt. Is it mainly the threshold voltage or? There are other aspects as well though, I assume the parasitic elements[4] play a role as well, especially when overclocking. [1]: https://en.wikipedia.org/wiki/Junction_temperature https://en.wikipedia.org/wiki/Junction_temperature [2]: https://en.wikipedia.org/wiki/Ohm%27s_law https://en.wikipedia.org/wiki/Ohm%27s_law [3]: https://en.wikipedia.org/wiki/MOSFET https://en.wikipedia.org/wiki/MOSFET [4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 [4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873
- mbajkowski 6y ago
  One thing that has to be considered and can become an issue with under volting is that multiple transistors make up circuits. Some times these transistors work together and some times they fight each other. Even two transistors in close proximity to each other on the same chip will be slightly different due to variation. As voltage decreases for some circuits this variation between transistors gets exposed as one transistor approaches the treshold voltage while the other may not, while at higher voltages this slight variation may not come into play as strongly, leading to outright failures or stability problems that get exposed at particular frequencies.
  - csharptwdec19 6y ago
    This is actually one of those cases where the 'Voltage as Pressure' analogy works well for a laymans explanation; with a lower voltage, the electons might not get pushed through quickly enough (Due to variations in manufacturing of the gates)

Did you use "lucky" here sarcastically, or do you actually need to be lucky with binning to be able to undervolt without issues? (I thought that was a concern with overclocking?)

londons_explore 6y ago

The same issues occur with both.

jchw 6y ago

Undervolting goes hand in hand with overclocking. The goal is higher clocks. The enemies are stability and heat. Undervolting reduces heat but the impact on stability depends on the silicon lottery. For mobile chipsets, undervolting at the same clocks is a nice performance uplift because of the reduced heat (on a system that undoubtedly does not have the best heat dissipation.) Overvolting is also useful for overclocking; at a point it can help increase stability. But generally I think you want to hit a point at which you are getting the highest clocks with the lowest voltage that is still stable.

mehrdadn 6y ago
Thanks!

magicalhippo 6y ago

Roughly, the transistors in a chip can have more or less internal resistance (Rds) due to impurities and variations during production. There's no way to know from one chip to the next until you try them. If it has less internal resistance it will generate less heat for the same amount of work. Semiconductors are constrained by the maximum junction temperature[1], and CMOS logic chips like modern processors primarily consume power when switching. So there's a thermal limit to how fast they can switch. Thus having lower internal resistance can allow you to clock higher (switch more often) before reaching the thermal limit. However, when switching they act as varying resistors, and the amount of power dissipated in any resistor depends on the square of the applied voltage (P = V^2/R). So if you can run your chip on a lower voltage, it will dissipate a lot less energy when switching, thus allowing you to switch faster before being thermally limited. When overclocking, you ask the transistors to switch faster. To turn a MOSFET[3] transistor on or off, you need to transfer a certain amount of charge (aka electrons) into or out of the gate. The faster you can transfer the charge (more electrons per second ie the higher the current) the quicker the transistor turns on. And the way to do that is to increase the voltage[2]. So overclockers tend to bump up the voltage when going for the super-high clocks. But as you see from above that causes a massive increase in heat, thus requiring significantly more cooling. I'm no semiconductor expert though, so I might got some of this wrong, but I hope I got the essence right. Also I'm not sure if the impurities and such that lead to the variability of the internal resistance is related to the ones affecting the ability to undervolt. Is it mainly the threshold voltage or? There are other aspects as well though, I assume the parasitic elements[4] play a role as well, especially when overclocking. [1]: https://en.wikipedia.org/wiki/Junction_temperature https://en.wikipedia.org/wiki/Junction_temperature [2]: https://en.wikipedia.org/wiki/Ohm%27s_law https://en.wikipedia.org/wiki/Ohm%27s_law [3]: https://en.wikipedia.org/wiki/MOSFET https://en.wikipedia.org/wiki/MOSFET [4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 [4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873

mbajkowski 6y ago
One thing that has to be considered and can become an issue with under volting is that multiple transistors make up circuits. Some times these transistors work together and some times they fight each other. Even two transistors in close proximity to each other on the same chip will be slightly different due to variation. As voltage decreases for some circuits this variation between transistors gets exposed as one transistor approaches the treshold voltage while the other may not, while at higher voltages this slight variation may not come into play as strongly, leading to outright failures or stability problems that get exposed at particular frequencies.
- csharptwdec19 6y ago
  This is actually one of those cases where the 'Voltage as Pressure' analogy works well for a laymans explanation; with a lower voltage, the electons might not get pushed through quickly enough (Due to variations in manufacturing of the gates)