Why did CPU clock speeds stop increasing? [duplicate]

Solution 1:

The first thing, remember that Moore's Law isn't a law, it's just an observation. And it doesn't have to do with speed, not directly anyway.

Originally it was just an observation that component density pretty much doubles around every [time period], that's it, nothing to do with speed.
As a side effect, it effectively made things both faster (more things on the same chip, distances are closer) and cheaper (fewer chips needed, more chips per silicon wafer).

There are limits though. As chip design follows Moore's law and the components get smaller, new effects appear. As components get smaller, they get more surface area relative to their size, and the current leaks out, so it makes you need to pump more electricity into the chip. Eventually you lose enough juice that you make the chip hot and waste more current than you can use.

Though I'm not sure, this is probably the current speed limit, that the components are so small they're harder to make electronically stable. There's new materials to help this some, but until some wildly new material appears (diamonds, graphene) we're gonna get close to raw MHz speed limits.

That said, CPU MHz isn't computer speed, just like horsepower isn't speed for a car. There are a lot of ways to make things faster without a faster top MHz number.

LATE EDIT

Moore's law always referred to a process, that you can double density on chips at some regular repeating timeframe. Now it seems sub-20nm process may be stalled. New memory is being shipped on the same process as old memory. Yes, this is a single point, but it may be a harbinger of the future.

ANOTHER LATE EDIT An Ars Technica Article all but declaring it dead. Was fun having you around for 50 years.

Solution 2:

Moore's law describes a long-term trend in the history of computing hardware. The number of transistors that can be placed inexpensively on an integrated circuit has doubled approximately every two years. It's not about clock speed.

Also, a CPU's clock speed is not a reliable indicator of its processing power.