Cooperstown39, terminology is important, so before I answer your question, some clarification of Intel's terminology is needed. The following is from Intel's specs:
"...the thermal specification is referred to as the junction temperature (Tj). The maximum junction temperature is defined by an activation of the processor Intel® Thermal Monitor. The Intel Thermal Monitor's automatic mode is used to indicate that the maximum TJ has been reached."
(1) Junction Temperature is obviously a temperature because it scales, so we have the term TJ, or Tjunction.
(2) Maximum Junction Temperature is a specification because it does not scale, so we have the term TJ Max, or Tjunction Max.
Since Tjunction Max is not a term familiar to most users who haven't read Intel's hundreds of pages of documentation, Tjunction and Tjunction Max continue to be a source of confusion in the C2D / Q2D community, somewhat due to the popular software utility "Core Temp".
In Core Temp 0.94 and 0.95, the author, Arthur Liberman, incorrectly shows Tjunction 85c (or 100c), instead of showing it as Tjunction Max 85c (or 100c) which is a non-scaling specification, and is technically the correct terminology.
Tjunction = Core Temp Tjunction Max = Shutdown (THERMTRIP) Spec
So to answer your question, ~ 5c below Tjunction Max throttling begins (PROCTHERM), and when Tjunction Max is reached, shutdown occurs (THERMTRIP).
Thank you for taking the time with the detailed explanation. As you can tell, I'm pretty new at this. I have read through some of the Intel documents and still confused with the temperature subject.
Below is a quote from the Intel Thermal & Mechanical Design document;
"The temperature where the THERMTRIP# signal goes active is individually calibrated during manufacturing and once configuration can not be changed."
Does this mean that the Tjunction Max is different for each chip? If so, are the software temperature programs using 85 and 100c as estimates for calculating temperature?
Also, could you confirm if my understanding is correct;
Tcase is the temp taken at the geometric center of the IHS. This is the temperature which is reported in bios as the cpu temp (?). Intel has specifications for Tcase max, in the case of a Core 2 Duo with 4MB cache it would be 72c. Although this is a specification, it was not clear to me if this parameter were exceeded that it would have any effect. In other words, would exceeding Tcase max. trigger the thermal control circuit (TCC)?
(2) Tjunction Max 85c (or 100c) is used by software utilities to determine Tjunction.
(3) Tcase is the CPU temp reported in BIOS.
(4) Stepping (not Cache) determines Tcase Max. Most are 60c. Some L2 and G0 Steppings are 72c.
(5) The single on-die CPU Case Thermal Diode is independent of the Cores, only measures Tcase, and does not trigger TCC.
Although Tcase typically scales ~ 15c (+ / - 3c) below Tjunction, Tcase and Tjunction are not alwas linear with respect to one another due to variables such as Vcore, clock speed and work load. The Digital Thermal Sensors (DTS) within the hot spot of each Core measure Tjunction, and are used to individually trigger TCC (TM1 and TM2), PROCTHERM, and THERMTRIP for each core. When Tjunction Max is reached and shutdown (THERMTRIP) occurs, Tcase Max has probably been exceeded, therefore, Tcase has no effect on triggering TCC.
For example, the E6400 L2 Stepping is Tcase Max 61c / Tjunction Max 100c, which makes absolutely no sense. At a throttle threshold of Tjunction 95c, even with an extremely high Tcase to Tjunction Delta of 20c, Tcase would still be 75c, which would far exceed Tcase Max by 14c. Permanent processor damage may occur when Tcase is sustained above 67c.
More typically, the E6600 B2 Stepping is Tcase Max 60c / Tjunction Max 85c, so at a throttle threshold of Tjunction 80c, with a Tcase to Tjunction Delta of 18c, Tcase would be a more reasonable 62c, which would only exceed Tcase Max by 2c, and not cause permanent processor damage. As you can see, when compared, some of Intels specs leave something to be desired.
Even if more recent C2D's (E6X50 Stepping G0 with Tcase Max 72c / Tjunction Max 100c) are designed with greater thermal tolerances to better cope with variables such as temperature fluctuations in high ambient environments, it is not recommended to continually operate processors, overclocked or stock, above Tcase 60c / Tjunction 75c, for reasons of stability, as well as longevity.