I think you should do something about it. Those temps are too hot, so underclock it back to its recommended specs or something, or check the thermal paste (if at all possible on a laptop) and the fans. If all else fails, maybe try a cooling pad. Laptops have a very narrow operating range due to their cooling limitations, and running at 100+C is not recommended, not to mention uncomfortable as it'll heat up everything around it, including the keyboard.

I would say from experience that most laptops run 45 to 60 degrees C idle, and 70-85 on load. But 100C is just too hot!

(that said I have not owned a laptop for several years - maybe they are more tolerant to heat, or are just meant to run hotter these days)

i5-3230M

What you are seeing is Turbo Boost kicking in.

Intel® Turbo Boost Technology dynamically increases the processor's frequency as needed by taking advantage of thermal and power headroom to give you a burst of speed when you need it, and increased energy efficiency when you don’t.

And since you haven't crossed its "danger zone" yet, it is trying to squeeze as much speed as it can.

Since you are running a very CPU intensive algorithm, the processor is ramping itself up to give you a little more oomph. My Lenovo laptop (also an i5) has several power option that can control performance and fan speed while on battery and plugged in. You might see if your Dell has something similar.

Yes definitely turbo boost thingie. But I would not expect it to wait for 105 degrees before spinning back to factory frequency.

The T-Junction is just the maximum temperature allowed at the processor die.

See Intel Turbo Boost, it explains some of the conditions that need to trigger to enable and disable it.

The clock speed is definitely turbo boost, but you definitely should not be seeing temps of 100 degrees, and the processor should really only get that hot if you have insufficient or faulty cooling. Be sure the air intake and exhaust ports aren't blocked, check to make sure the fan and heat-sink are free of dust and debris, and blow them out with compressed air. You may have to partially disassemble the laptop to get at the CPU heat-sink (usually in a laptop, the heat-sink consists of a heat-pipe to some small fins near the exhaust port -- while you're in there, make sure that it looks like the heat-sink is seated properly. Also try running the laptop in a normal orientation rather than on its side -- the laptop is designed to work in a certain orientation; a good design ought not be so affected, but its possible the orientation is contributing to the problem and it'd be good to at least eliminate that as a possibility.

Its possible that this particular workload might put the CPU into some kind of pathological state -- either the CPU design in general, or perhaps your particular CPU due to a manufacturing defect. If the above doesn't help, your only recourse is to accept it and keep a close eye on it, try to get a warranty replacement, or perhaps you could use a CPU tweaking tool or the bios to under-clock/under-volt or be more aggressive about throttling itself a bit sooner (though, these options will give up some performance).

By the way, a normal load temp with sufficient cooling should be between 80-90 degrees C, although it depends somewhat on the ambient temperature.

Good luck, and let us know if any of these suggestions help, or if they've made no difference.

Even, as he described, under heavy load continuously for 20 minutes?

It really shouldn't from everything I know -- Heck, most overclockers recommend to keep temps under 90 degrees -- I mean, keep in mind we're talking centigrade here, 100C is literally hot enough to boil water. Its probably not a horror to hit it occasionally and then throttle, but any sustained time at that level would be enough to concern me that something's wrong with my cooling.

When my liquid cooling loop failed earlier this year, the CPU temp would peg itself at 100C by the time I made it to the windows desktop, the CPU was throttling itself all the way down to 800Mhz, and it would then crawl a bit higher before forcibly shut itself off after a few minutes -- a few degrees above 100C is actually the thermal tripping point for modern Intel CPUs, if it were to go much higher than OP is saying he sees and stay there, its got to be very close to turning itself off.