Can someone explain clock cycles in simple terms?

[Lysander]

OK, I don't know that much about the workings of CPUs, but I know that the rule used to be, the more Ghz, the faster the processor.

However, now I'm told that it's not just about clock cycles per se but the quality of the cycles. What does this all mean?

Does this mean that a P4 2.8Ghz is less fast and effective than a e6600 at stock?

 

[Lysander]

In simple terms, core 2 cpus do a lot more work for every clock cycle than a PIV cpu,

OK... I understand this so far. Could you elaborate in layman's terms?

 

[Lysander]

An E6600 is probably closer to twice or maybe even three times faster than a P4 @ 2.8GHz.

Do you know much about car engines? Think of clock cycles as the revs. Think of the "quality" of each cycle as torque.

Or another analogy... big shovel means you can shovel more coal but at a slower rate. A smaller shovel means you can shovel smaller amounts of coal but at a faster rate. A Core 2 Duo would be the former and a P4 would be the latter.

Technically it's all down the length of the CPU's pipeline and it's "branch" prediction. Any time a piece of software comes to a line of code that asks a question (e.g. "Is 5 more than 100?") can cause a pipeline flush if the CPU predicted it incorrectly. A pipeline is basically the way a chunk of work is broken up into smaller pieces. For instance the previous example might get broken up into maybe 4 chunks on a P4 chip but on a C2D it is almost certainly just one chunk in the pipeline. This means the C2D can push other instructions into the pipeline from the saved space.

Right, this is very helpful. An anology that helps me is:

Let's say you have a road, and the width of that road lets 1000 cards go down it per hour. Now, if you treble the width of the road, but slightly degrade the surface, it means that more cars can go down it, but slightly slower. This would mean that in spite of the fact that the cars are going slower, more of them can get through i.e. more information is processed.

I've been looking at Wikipedia and trying to understand the concept of clock cycles. Can anyone briefly explain them?