What Do people mean when they say.....

[grchris32]

My question is what do people mean when they compare 2 CPUs from different families and say "they are from a different family of cpus so their clock speeds are by no means directly comperable"
What do they mean how does that change, yes they have better architecture yes they may have more cores and cache but for all i know ghz is a cycle measurement to measure calculations. how does a new 3.40 ghz cpu achieve more calculations over a bit older 4.30ghz cpu? Or maybe it actually doesnt? this only has to do with calculations and not games. so just keep that in mind (yes games require calculations but its a bit complicated)

 

[sizzling]

IPC or Instructions Per Cycle. This is how much work the cpu can do per clock cycle. Therefore a higher IPC can allow a slower clocked cpu to do the same or more work than a higher clocked cpu with lower IPC.

 

[little_me]

It has to do with Instructions Per Cycle or IPC
https://en.wikipedia.org/wiki/Instructions_per_cycle
meaning that each clock cycle, CPU can do X amount of things. Which means that old 4.3Ghz core can't keep up with new 3.4Ghz core.
What are the instructions? look at assembly code language and you get pretty close although that also skips a few steps.
https://en.wikipedia.org/wiki/Assembly_language


Of course, it isn't clear "One family equals double performance" steps but if you compare across 4 or 5 steps (like old intel I7-3700 and new 9700) you will see decent step up in performance per clock. (maybe 5%/family but.. Intel slacked a bit in last few generations so totals to like 15 to 20% at most)

 

[xeddiex]

You really cannot compare CPUs by just the clock speeds.

You need to consider other things like "Number of cores/thread", which implies to "Performance per core/per thread".
Cache matters too, the more the cache capacity, the less time the CPU requires to access data from the memory.
CPU architecture (e.g. 22nm/14nm) also comes in when you are looking at heat/power consumptions.

If you are ignoring all those, then you could see people go like "Oh, even a Pentium4 4.0ghz from the years back beats the modern i7 (e.g. 8700K with 3.7Ghz), because the clock speed is faster".