"Temperature Monitor" works well and answers other Qs
Thank you both for recommending "Temperature Monitor."
Now to give back to the community: Here's an exerpt from the "Temperature Monitor" literature that I think will answer both of the further questions. You can also go to the website.
How does the program measure the CPU temperature?
There are two cases to distinguish here:
a) You have a Macintosh system with an "older" PowerPC processor,
b) you have a machine with a PowerPC 7450 or later processor.
In case (a), temperature measurements are based on a component inside the processor itself, known as "Thermal Assist Unit (TAU)". This unit uses a physical effect in the PowerPC processor to guess the current temperature directly at the die-junction, the connection between the silicon chip and the ceramic base. Unfortunately, this technique is very unreliable, depending on CPU load and other circumstances: Measured values can fluctuate very rapidly and can generally be off by 12 degrees Celsius (21,6 degrees Fahrenheit). For those reasons, Motorola has disabled the Thermal Assist Unit on the PPC 7450 and later processors.
In case no TAU is available (b), Temperature Monitor will look for a sensor built into your computer to get its temperature values. Apple has equipped all the latest Macintosh models that require intensive cooling with their own sensors, essentially to control the built-in fans and prevent overheating. Those sensors are very reliable and much more accurate than the TAU-based solution.
If your computer has a PPC 7450 or later but no temperature sensor was built in, no measuring is possible.
What is the "normal" temperature for current CPUs?
This depends on the particular model, but CPU temperatures between 122 and 158 degrees Fahrenheit (50 to 70 degrees Celsius) can be expected for all up-to-date computers. Some specification values for G4 processors used in the MDD and FW800 models are given by the following table. Note that the official temperature limits are defined for measuring at the die junction. The Macintosh temperature sensors are not at the CPU die itself and are not in contact with the heat sink which means the measured temperature may be higher than the die junction temperature.
