Intel Core 2 Quad Q9505
The second LGA775 processor we selected to participate in our power consumption tests is a quad-core Core 2 Quad Q9505. This CPU doesn’t have a unique semiconductor die and is based on a combination of two Wolfdale dies manufactured with 45 nm process. Therefore, it is not surprising that this double die aka Yorkfield has unusual structure of the L2 cache memory that consists of two 3 MB parts, each shared between two cores. As for the frequencies, Core 2 Quad Q9505 works at 2.83 GHz nominal clock and supports 333 MHz FSB that serves not only to connect this processor with the chipset, but also to ensure proper communication between the core pairs that do not share any cache-memory.
It would be quite logical to expect the typical TDP of a quad-core processor like that to be twice as high as that of dual-core Core 2 Duo based on Wolfdale core. However, this is not quite the case: Core 2 Quad Q9505 TDP is set not at 130 W but at only 95 W. Of course, lower CPU clock frequency than that of the dual-core solutions is definitely a factor here as well as the peculiarities of the employed production process. The thing is that Intel selects semiconductor dies with better heat dissipation readings for their quad-core processors. As for less energy-efficient dies, they are being cut in half for dual-core processors. Therefore, it is not surprising that during our tests of the Intel Core 2 Quad Q9505 processor in nominal mode, its power consumption under heavy load was only 70 W. the total system power consumption in this case was about 125 W, which can be considered yet another piece of evidence that LGA775 platform is more energy-efficient than Socket AM3.
Overclocking quad-core LGA775 processors is not the easiest task to complete. The thing is that at certain bus frequency these processors start “acting out”, and very often the problems occur at 450-475 MHz FSB speed. Luckily, Core 2 Quad Q9505 has a relatively high multiplier of 8.5x, which allowed us to overclock it to 3.9 GHz without any serious problems. I have to say that just like with Core 2 Duo E7600, our quad-core test CPU worked stably at 3.6 GHz frequency and its default Vcore of 1.275 V.
To investigate the way power consumption changes during overclocking we tested Core 2 Quad Q9505 with 200 MHz increments, just like in all other cases. The major system parameters are listed in the table below. All other system voltages remained at their default values during this test session:
So, the system power consumption under full processor load depends on the CPU frequency as follows:
Since Core 2 Quad Q9505 overclocked pretty well in relative terms, we managed to take the power consumption readings off seven different knots. As a result, we can clearly see that if the processor core voltage remains constant, the dependence between its clock frequency and power consumption remains linear. After that, as soon as we pass 3.6 GHz mark, where not only the clock frequency but also the CPU Vcore start to change, every 200 MHz increase costs about the same in terms of power consumption as every 600-800 MHz before the 3.6 GHz mark. Overall, 27% frequency increase from 2.8 to 3.6 GHz produced a 19% increase in power consumption. However, overclocking to 3.9 GHz caused a 50% power consumption growth compared with the TDP in nominal mode.
As for the power consumption along different power lines, we can say that just like in the previous case overclocking causes a natural increase in currents going along 12 V power line assigned to the processor voltage regulator. Also the currents increased along 3 V mainboard power line, which we believe feeds the chipset North Bridge.
Processor working at its nominal frequency under 100% load in LinX test consumes 71 W of power. At 3.6 GHz frequency, when its Vcore remains at the default 1.275 V, its power consumption hits 89 W. during maximum overclocking to 3.9 GHz, when all major system voltages get set about 10% above their nominal values, processor power consumption rises to 136 W. this is, certainly, a lot, but it can’t compare with the power readings taken off the overclocked Phenom II X4. Therefore, the conclusion we drew above about LGA775 processors still being more energy-efficient than their Socket AM3 alternatives not only in nominal mode but also during overclocking remains intact and true.