In layman's terms, what are Instruction set extensions for the CPU?

[7thwraith]

I was comparing the i7 3770K vs i7 3790k. My thirst for comparison and more information led me to this website and URL:
http://cpuboss.com/cpus/Intel-Core-i7-4770K-vs-Intel-4790K

It seemed fairly clear that the 3970k is the better choice. But then I scrolled down (a ways; about 3/4 of the way down the page in "Specifications") and saw that there were a bunch of features that the 3790k decided to cast off.

I don't think I will be purchasing either of these processors (I have an i5 3570k and it's just fine for even CPU-intensive gaming), but I was very curious about what the difference is in these two processors. It seems that the 3790k gave up some features that the 3770k had in order to make space for pure computing power.

Is that correct? And what do these features do in simple-talk?

thanks.

 

[Dark Lord of Tech]

That site is useless.

 

[7thwraith]

That answer is useless.

And even if the site is useless, extension set instructions are still a feature of some modern CPUs. I googled it, but the only thing that popped up was in engineering jargon.