EIST In Intel's New 45nm Processors

Since I wrote this article, I sold my Core 2 Duo E6850 processor so I would not be able to provide exact figures for the comparison against the new Intel 45nm Core 2 processors. But the main reason for the huge drop in the power consumption of the Core 2 Duo E6850 processor is due to the CPU voltage changes using EIST.

If I recall correctly, it reduced the CPU voltage by about 0.2 V when EIST is enabled. You can see this in the table on the right.

Although it's just 0.2 V, it is actually a substantial decrease in voltage of 16-19 %. This is a very good thing as any increase in voltage is a major cause of higher power consumption and heat output.

Hence, the E6850 benefited greatly from EIST, saving up to 36 W of power at idle. That's 19.4 % lower power consumption and thermal output. However, things were not the same with the newer 45nm Core 2 processors.

I replaced my E6850 with the new E8400 (Wolfdale) processor. Despite having the same 9x multiplier, EIST wasn’t as effective on E8400 as it was on the E6850.

With EIST enabled, the voltage in the E8400 only decreased by just 0.07 V! Even when I overvolted the processor to 1.25 V, EIST did not reduce the voltage to the level we saw with the E6850. In fact, it only reduced the voltage by 0.06 V. The ABIT IP35 Pro doesn’t allow undervolting below the stock voltage, so this is the lowest I could go.

That is extremely disappointing as the voltage reduction is only in the region of 5-6 %, a far cry from the 16-19 % voltage reduction we saw with the E6850. Naturally, the reduction in power consumption was far lower than what we saw with the E6850.

At 3.8 GHz, EIST only reduced the E8400's power consumption by 12 W. When overvolted and overclocked to 4.05 GHz, the reduction in power consumption was even less significant at just 6 W. This more or less parallels the reduction in CPU voltage we saw with EIST enabled.

I couldn’t find any useful information about this limited VID range problem online. I only managed to discover that the supported VID range of the E8400 was from 1.125V to 1.250V. If you know the reason for this limited drop in CPU voltage for the E8400, please do let us know!