performance - Why have CPU manufacturers stopped increasing the clock speeds of their processors?

I have read that manufacturers stopped concentrating on higher clock speeds and are now working on other things to improve performance.

With

• an old Desktop machine with Intel® Xeon® Processor E3110 with clock speed of 3.0GHz


• and a new server with AMD Opteron(TM) Processor 6272 with clock speed of 2.1GHz

when performed a simple encryption comparison using (single threaded)

 openssl aes256c

the desktop performed far better than the server.

So even with latest optimization, why does the processor with the better clock speed perform better?

Answer

The reason manufacturers have stopped concentrating on increasing clock speed is because we can no longer cool the processors fast enough for this to be viable. The higher the clock speed, the more heat is generated, and we've now hit a stage where it is no longer efficient to increase processor speed due to the amount of energy that goes into cooling it.

Other answer goes into detail on how higher clock speed doesn't mean better performance in all areas.