Overclocking--130 Watt Speed Limit
Overclocking Made Difficult
Overclocking is very different on the Core i7. Unlike the Core 2 or Pentium D processors, the Core i7 CPU can monitor the current it draws as well as its power consumption—if it exceeds a certain level, the processor automatically reduces its clock speed. Intel calls this feature "Overspeed Protection." The limits hard-wired into the core are 100 A and 130 watts. Only the Extreme Edition allows the user to increase these values as they like, effectively circumventing the protection mechanism altogether.
Thermal power loss rises especially quickly when the core voltage is increased. Thus, it is entirely possible that a lower model Core i7 may offer excellent overclocking potential, but it will be constrained by the Overspeed Protection feature when its power dissipation triggers it. Obviously, Intel wants to prevent customers from buying an inexpensive processor and then overclocking it to very high or even extreme levels. Apparently, Intel has realized that the good overclocking potential of its processors has led ambitious users to choose less expensive models, relegating the faster (and more expensive) CPUs to the sidelines.
Companies selling water-cooling solutions may also be affected as an unintended consequence of this design. After all, water cooling solutions tend to be the method of choice in scenarios where a conventional air cooler is no longer able to handle a CPU’s heat dissipation. The normal, non-Extreme Edition Core i7 processors will hit a hard limit at 130 watts, which means a large percentage of users who previously chose a liquid cooling solution may suddenly disappear. Instead, the target group for such pricier cooling solutions would automatically shift to buyers of Extreme Edition processors and users building silent PCs.
Buying the Right CPU? Luck of the Draw
Intel’s thermal design power (TDP) rating is meant to specify the maximum amount of power a certain CPU will draw under full load when running at its default clock speed and using its stock voltage. As mentioned above, all current Core i7 models have a maximum TDP of 130 watts. It is entirely possible that a given Core i7 940 or 920 may actually only consume 70, 90 or perhaps 110 watts. If you are lucky enough to find yourself with a 70 watt version, that gives you an overhead of about 50+ watts for overclocking, and you’ll be able to increase the core voltage enough to see some good results. Conversely, if you end up taking a 110 watt model home, you’ll only have 20 watts of overclocking headroom before the CPU begins to throttle its clock speed. In this case, the same model of a CPU will offer much lower overclocking potential due to the Overspeed Protection feature.
A highly efficient cooling solution may give you a little more room to maneuver by reducing thermal power loss. Still, this will only let you eke out a few more megahertz. Our thermal dissipation measurements on the 45 nm Core 2 CPUs have shown that the power consumption can vary greatly from one model to another; the Core i7 models will be the same.
who knows?
