piotrr said:
Not to question a fellow - and obviously systematic - overclocker, but have you experimented with relatively LOW voltages? My very first experience of Winchester overclocking was that I overestimated the requried voltages and had much better success once I cut back a little on VCore.
I know, I know, it's almost an automatic impulse to raise speed, cooling and voltages, but hold back on voltages a little and at least I discovered better stability (and thus higher OC) when I didn't raise voltages as much as my heart told me to. I reach 2500MHz at 1.36V.
The 90nm A64 is a beautiful beast.
Welcome to the forums.
It is OK to question my posts which can be incomplete, not clear or erroreous.
It is correct that bare minimum voltage should be used, especially at maximal overclocking. This is why.
Bare minimum voltage at maximal overclocking
Voltage, frequency and temperature are the three key variables in overclocking. There is a delicate, natural balance between them at maximal overclocking.
In general, higher voltage provides higher transistor switching current (active current), hence shorter logic gate delay so that a faster clock can be used.
But higher voltage leads to higher active power (C V^2 f) and higher leakage current and power (I^2 R), hence resulting in higher temperature, where V is voltage, f is frequency, I is leakage current, C and R are respectively equivalent capacitance and resistance to model active power and leakage power. Higher temperature slows down the chip due to decrease in electron mobility, and higher leakage current and power which further lead to temperature increase.
So when voltage V is increased to substain certain frequency f, at the beginning of overclocking it is usually easily achievable. When the system reaches certain point of overclocking, equilibrium occurs and further increase in voltage will result in higher temperature which will counteract further increase in frequency due to lowering of electron mobility and even faster rate of increase in leakage current and leakage power over voltage (leading to postive feedback and run-away temperature). Overclocking has then reached the limit for a given cooling. In order to clock higher, better cooling is needed to further contain the temperature, so further speed can be increased.
So when overclocking is far from its maximum, voltage that is higher than what is needed does not matter. But
when it is close to the maximal overclocking, bare minimum voltage that is just sufficient to substain the CPU speed should be used. Otherwise the extra "wasteful" or "overly applied" voltage may even diminish an otherwise better overclocking result (frequency). There are many cases, at time, one will see that
by reduceing an overly applied voltage, say by a small step, the system stability improve and may even be able to clock slightly higher.
Ref:
hitechjb1 said:
Voltage, temperature and frequency: the basic variables of overclcoking
Voltage, temperature and frequency are the three basic variables for overclocking. These posts describe the relationship between them, using Tbred B/Barton as examples. The underlying concepts can be applied to other silicon type of CPU's and chips.
The effect of voltages on frequency and failure time are also discussed.
CPU voltage: from stock to max absolute, from efficient overclocking to diminishing return (page 19)
On CPU life expectancy and the tradeoff with voltage and frequency (page 19)
What is an ideal and safe temperature for overclocking (page 19)
Why high voltage is needed to run higher CPU frequency (and maybe higher FSB) (page 20)
Relationship between CPU frequency and temperature (page 20)
