Question

Why haven't CPU clocks speed increased in last five years ???...​

Answer 1

There are many reasons under different categories and I'll try to touch on them all.

Power:

When designing the micro-architecture of a CPU, one of the key design decisions is how to achieve higher performance. During the days of the Pentium 4, Intel (company) chose to go with very high clock speeds with a relatively narrow pipeline. This approach has many advantages: one being that it is easy to speed up single-threaded, serial code. Not a lot needed to be done in software to parallelize instructions and most software would immediately see benefits.

However, this approach also has its flaws: ignoring the implementation flaws of the Pentium 4 itself, we'll only speak of the flaws in the concept itself. Mainly that CPU's were hitting a power wall and that high-frequency micro-architectures are not very suitable for many of the low-power design techniques that had been invented to deal with the power issue. I'll touch on the two major low power design approaches here.

hope this answer helpful u