Risk-free Overclocking, Including Heat Protection
The Pentium D supports version 2 of Intel's Thermal Monitor, a protective mechanism that enables the system to keep running and also prevents damage to the processor itself. Thermal Monitoring has been around since the Pentium 4 (Willamette) was introduced in 2000. If the CPU exceeds a specific temperature threshold, the clock controller for the processor automatically throttles back from time to time. This causes power consumption (and thus also heat output) to diminish quickly, though obviously performance will suffer noticeably.
The reworked Thermal Monitoring 2 is smarter, because the clock controller no longer skips clock cycles, but rather throttles back the processor clock rates. For this purpose, the controller likewise uses the PROCHOT signal, to allow the system to keep running smoothly, albeit at a reduced clock rate. Because the activation of PROCHOT as a protective mechanism through Thermal Monitoring 2 occurs right in the processor, neither BIOS updates nor settings changes are needed. The already described Enhanced Halt Mode C1E takes this one step further, and applies this when the idle process is running in the operating system.
Block diagrams of the workings of Thermal Monitoring 1 and 2.
Because Thermal Monitoring 2 provides a form of "overheating insurance", as it were; it's easier to overclock systems with this capability. Should the system overheat, it also reacts noticeably better than a system protected by Thermal Monitor 1. Thus, the second version of Thermal Monitor offers an additional bonus for overclockers to exploit.