The CPU list

This document aims to be a comprehensive list of CPUs and their recommended temperature limits. So far, only fairly recent CPUs are listed; contributions to this list are welcome!

In order for mondo to read the temperature of a CPU, there must be an lm_sensors-supported hardware device connected to a temperature monitor in or near the CPU. There are generally two ways this is done: thermal monitoring logic built in to the CPU, or a thermistor circuit built into the motherboard. The former solution is universally regarded as superior, since it can provide consistent, accurate, up-to-the-instant reporting of the CPU's internal temperature, regardless of what motherboard the CPU is installed on. Motherboard thermistors, on the other hand, are rarely consistent between two motherboards and generally cannot give accurate, up-to-the-instant reporting.

Pentium 4:

These CPUs have built-in duty throttling that will partially idle the CPU if it starts to overheat; if (for some reason) this is not enough to stop the CPU from reaching 70 C, the CPU will hard-lock in an idle state. Usually the hard-locked idle state is never reached, even if the CPU heatsink is removed. This makes it nearly impossible to fry the CPU without modifying it somehow (like overvolting it, as some overclockers do). So in this case, there's not much need to set an alarm threshold.

Athlon (Slot A):

These CPUs have no built-in logic for thermal monitoring or thermal protection. If you remove the heatsink completely from such a CPU, it will likely fry within a few minutes (though perhaps not instantly, as Slot A CPUs do have a heat spreader). Some motherboards have thermistors which can detect approximately what temperature such a CPU is running at, but the accuracy of these thermistors is inconsistent and always questionable. 90 C (90 degrees Celcius) is the specified temperature when latent damage starts to occur on an Athlon; the CPU may crash or begin to show sporadic problems at any temperature between 60 and 80 C. Once the CPU crashes, mondo will become ineffective, and the CPU will probably continue to get hotter and hotter until it fries itself.

50C would probably be the maximum upper threshold for CPU temperature.

Athlon (Thunderbird, Duron, Spitfire)

The situation is similar to Slot A athlons, except that motherboard thermistors are somewhat more accurate, and the Thunderbird will not survive running without a heatsink. A Thunderbird without a heatsink will probably fry within a few seconds; a Thunderbird with a heatsink (but no fan) should last at least five minutes (this from personal experience and user reports).

60C would probably be the maximum upper threshold for CPU temperature.

AthlonXP, AthlonMP, DuronXP:

These CPUs run rather cooler per clock than Thunderbirds. Fortunately, they have built-in thermal monitoring logic. Unfortunately, this built-in logic will not actually do anything special if the CPU starts to overheat (i.e. it will report the temperature, but it won't do anything more to stop the CPU from frying). Even more unfortunately, most Athlon motherboards, even those designed for the AthlonXP, do not enable reading of this built-in logic, and continue to rely on less accurate, less effective motherboard thermistors.

If you have one of the rare motherboards that reads the AthlonXP's on-die thermal monitoring logic (such as an Asus A7V333), 70C is probably a good maximum upper threshold for CPU temperature. Some of these motherboards have built-in logic that will not only enable use of the CPU's thermal monitoring logic, but will also take care of shutting the system down if the CPU starts to overheat. However, this has been known to fail from time to time, so it's safest to set an upper limit for CPU temperature in mondo as well.

If you aren't sure your motherboard supports the AthlonXP's built-in thermal monitoring, you should use the same limits you would use for a Thunderbird (listed above).

Mobile AthlonXP (used in some laptops):

These CPUs come in two varieties. The older variety (usually found in desktop replacement notebooks) is almost exactly like the desktop AthlonXP, so the notes for AthlonXP's also apply here.

The newer variety of mobile AthlonXP's comes in 130-nanometer, low-voltage packaging for thin-and-light notebooks. It consumes far less power than a desktop AthlonXP, but its temperature tolerances are probably the same. I can't be sure though.

Pentium 3 Coppermine (700MHz to 1GHz):

These CPUs don't run quite as hot as Athlons. In addition, they include built-in thermal monitoring logic that will hard-lock the CPU in an idle state if it starts to overheat (anyone know the documented temperature for this?). These CPUs are difficult to fry without overvolting; they usually survive even if the heatsink is removed. Thus an alarm threshold is not really necessary for these CPUs, unless you want to preempt the hard-locked idle state in preference of a graceful power-down or some other mildly useful alarm action.

Pentium 3 Tualatin (800MHz to 1.4GHz):

These CPUs run considerably cooler than Pentium 3 Coppermines, but the same notes for Coppermine also apply here.

Pentium 3-M (used in some laptops):

This is usually a scaled-down version of a Coppermine or Tualatin. The same notes for Coppermine and Tualatin also apply here.

Pentium 3 Katmai (450MHz to 600MHz):

Not much known. Anyone care to comment?

Pentium 2:

Not much known. Anyone care to comment?

VIA C3 Samuel (866MHz to 933MHz):

Credit for this information goes to Fraser McCrossan.

These CPUs are targeted as low-power, inexpensive replacements for Intel Socket370 CPUs (such as Pentium 3 Coppermines). Although it is not yet known if these CPUs include on-die thermal monitoring logic, it is a fair assumption that, as pin-compatible Pentium 3 Coppermine clones, they do. However, this does not necessarily protect the CPU--it could very well just report the temperature, and nothing more, much like the AthlonXP.

These CPUs are guaranteed to function with an "Operating Case Temperature" of 0-70 C. They can supposedly withstand higher temperatures for short spells, but nothing is guaranteed once the 70 C mark is broken. So 70 C is probably a good upper threshold for this CPU.

Alpha CPUs:

Not much known. I strongly suspect that everything up to the 21264 (EV6x) series has no built-in thermal diode. Reportedly some UPxx00 series motherboards carry a thermal diode, but as I don't actually have one of these motherboards, I can't confirm or deny these reports, nor ascertain how well these thermal diodes work. I also know nothing about current generation EV7 (21364) CPUs.

I can tell you for certain that a 21164A (EV56) on a PC164LX has no thermal monitoring hardware.

Pentium M Banias (used in Centrino laptops):

Notebooks branded with Intel "Centrino" technology feature a new Pentium M CPU, codenamed "Banias." The CPU is, for the most part, an enhanced, low-power Pentium 3 that's designed to interface with recent Pentium 4 chipsets. (It's not pin-compatible with desktop Pentium 4's, by the way.) I would expect it to have heat tolerances and protection mechanisms equal to or better than the Pentium 3 "Tualatin" CPUs. I don't know for certain, though.