AMD's Opteron 250 vs. Intel's Xeon 3.6 GHz in a Workstation Duel of the Elite

Heat Loss Decreases With Demand-based Switching

In contrast to the Desktop P4 processors, Intel is now delivering the first Nocona Xeons with DBS. This is based on what is known as demand-based switching, which Intel will also deliver in the form of IEST or Intel Enhanced Speedstep Technology from now on. It is a well-known principle: If only a small amount of processing has to be done, the fast processors lower their clock speed (from 3.0 GHz), if required, by up to 2.8 GHz, while at the same time the core voltage is also decreased slightly. As a result, heat loss is decreased and energy is saved without any loss of performance.

If, on the other hand, high performance is required, heat loss remains close to the maximum. So no savings can be made on the heatsinks on the basis of these new features. Even more aggravating is that at the moment there is no easy way to distinguish the DBS-capable processors from the conventional Nocona Xeons. The only thing that can be done is to get a read-out of the CPUID.

DBS occurs without the assistance of the operating system while the machine is in operation, and calls for a correctly programmed ACPI Table. The manufacturer of the motherboard is responsible for that. So if corners have been cut in this respect, it is quite probable that the feature cannot be used. However, if it is running, then it will continue running - to our knowledge, DBS cannot be disabled.