Can it be true?

I've just upgraded from an Intel P4 socket 478 that ran avg. 55C, and at load it would get up to 75C.

I just got an AMD Athalon 64 5200+ AM2, plugged it in with the stock heatsink/fan and it's yet to go over 40C (even at full load!) and it made me wonder if it's giving incorrect readings or are these CPU's just that much cooler?!

The intel P4 Prescotts were well known for being a replacement heater during the winter time. What you're seeing is fairly typical.

I agree, Pentium 4's were using a system where they'd push as much clock as possible to get the job done, and the harder you push a CPU, the hotter it gets. AMD took a different approach, even since Athlon XP, their chips do more per clock cycle, thus enabling them to build a 1.8GHz chip and have it go toe to toe with a Pentium 4 3GHz CPU (K8 processors are my reference). I don't think AMD has officially acknowledged it but their naming references the Pentium 4 equivalent of that specific chip, so an AMD Athlon 64 3000+ @ 1.8GHz is going to perform like a 3000MHz (3000MHz <1000MHz = 1GHz> = 3GHz). Sometimes it would even go above that, it's circumstantial and if I remember correctly AMD's chips do this magic trick in bursts, so that 3000MHz equivalency isn't constant. Anyway, my Athlon XP 1800+ (1.5GHz) idled at 46c and at load it hit 52, my opteron never goes above 44c.

Were they really used as room heaters? That is kinda funny. What you used to do during summer? Leave the unit outside!!!

Let's just say you have to run your air conditioner on HI!
But a lot of people worked on advancing water and other methods of cooling.
We got better heat sinks,cooling systems,fans, that were adapted to all sorts of uses,
Vcards motherboards and other chips, so we all benefited from better products.
And a little hot chip started the revolution lol.

back when I was using that Pentium 4 I had just bought Doom 3. It was the middle of summer and we didn't have air conditioning! It was over 95 degrees in my room and if i tried to start playing Doom 3 I would see a whole bunch of white specks on the screen (was a 9800PRO video card at the time) I was only able to play the game at night when it was cooler. I also put a fan up to the case which helped for about 20 minutes then i'd get the same white specks. When I say white specks I mean so many white specks that you can barely see what's going on in the game!

Do you have any problems with your AMD chip?

no problems at all. This is my first AMD build and it's been great. the stock heatsink/fan has kept it below 40c all the time!

My AMD AM2 5600+ I've had for 6 months idles at 40C and peaks both cores at 55C when running F@H SMP folding at 36 hour intervals.
Its been the best AMD CPU I've ever owned and the price was right when I bought it!