CPU Differences

[SImoHayha]

 

Here is my response I gave to someone else a while back

 

Performance is about the architecture and not the number of cores, GHz, or cache. Computers process instructions and tend to get a set amount done per clock cycle. This is known as IPC or instructions per clock cycle. When comparing AMD to Intel, or even AMD vs other AMD lines, it is about the architecture.

 

Now I'm going to make up some numbers here for example. We're going to have a 6 core 3.6 GHz against a quad core clock at 3.7 GHz. Each core in the 6 core has a IPC of 2 instructions per clock. So if we take 2 instructions times it by how many clock cycles it has in a second (3.6 GHz which is 3.6 x 10^9). You get 7.2 x 10^9 instructions per second for one core. Now also for this example we're going to pretend the processors have perfect multicore scaling. So we have 6 cores doing 7.2 x 10^9 instructions a second or 43.2 * 10^9 instructions per second for the 6 core.

 

Now the 4 core is newer and much more efficient. It averages 3.5 instructions per clock cycle and its clock cycles per second is 3.7 GHz. So 3.5 x (3.7 x 10^9) or 12.95 x 10^9 instructions per second for a single core. Now there are 4 cores so 4 x 12.95 x 10^9 equals 51.8 x 10^9 instructions per second for the newer quad core. As you can see the quad core easily beats the 6 core, it would even easily beat it if you downclocked the quad core to 3.5 GHz (49x10^9 vs 43.2x10^9). Now you may be thinking stuff like this doesn't happen often outside of examples, I used the FX 6100 and the Athlon 860k as examples. (IPC I still made up cause i don't have access to that info).

FX 6100

http://www.cpubenchm...X-6100 Six-Core

Athlon 860k

https://www.cpubench...ad Core&id=2362

 

Intel has a huge lead over AMD in IPC. Which is why the 8 core AMD FX 8350 sits behind the lower clocked 4 core I7s and 6 core I7 Extremes.

 

Might want to change the text to auto...its black on the night theme.

[tmlhalo]

Might want to change the text to auto...its black on the night theme.

I'm in a good mood, so sure. Done.

[tmlhalo]

If anyone wants the very long version here are slides from an old college course. CPU performance starts on page 27. 

http://faculty.uscupstate.edu/ntobias/documents/310_docs/Presentations/F14/Chapter%201.pdf

[Glenwing]

Why, though?

 

Hertz is a generic unit which means cycles per second. It doesn't define a CPU's performance alone. What exactly a "cycle" entails will depend on the CPU design in question, how the transistors in it are configured and how many there are. Likewise a "core" is a generic term, and some core designs will be able to do more computations per cycle than another. So when you have an "8-core 4.0GHz" processor, that's not an absolute measure of computational power. It tells you the performance relative to other processors using the same core design, but when you bring in chips with different designs, they are meaningless numbers. 1GHz (1 billion cycles per second) of one design doesn't accomplish the same amount of computation as 1GHz with a different design.