Comparison of Desktop and Laptop CPU speeds

[Nitin Giri]

I have always had this doubt that how a desktop CPU and a laptop CPU running on the same speed have a performance difference. Theoretically two CPUs running at the same speed should have the same performance right? For example take a Lamborghini Gallardo running at 100KM/h and a Suzuki Swift running at exactly the same speed. Irrespective of their engine power, they should cover the same distance at the same time (assuming they are running at the same speed constantly). Similarly two different CPUs running at the same speed should execute the instructions at the same time right? But why is that not the case?

 

[Icaraeus]

Laptop CPUs are very low power and aren't directly comparable. Let's say you get a good laptop Intel Core i5, that has 2 cores and a 3Ghz clock and draws less than 20W. An equivalent desktop Intel i5 has 4 cores and a 3.8Ghz clock and draws 50W. Similarly, an Intel Core i7m (laptop) has 2 cores + hyperthreading (4 threads) or up to 8 threads for the expensive CPUs, whereas desktop i7s are generally close to 4Ghz and have 4, 6 or 8 cores as well as being hyperthreaded (16 threads for the i7 5960X).

 

[Nitin Giri]

Hi Icaraeus, what if we compare a laptop and a desktop cpu having the same number of cores/threads and having the exact same speed? Will they have the same performance irrespective of the TDP?

 

[Icaraeus]

Assuming a laptop CPU would be able to do that (which it wouldn't, the socket would melt almost instantaneously), depending on the CPU architecture (Sandy Bridge, Ivy Bridge, Haswell, Broadwell etc.) the performance would be pretty similar. Depending on the CPU generation, one would be a little faster than the other (i.e. Haswell is 5-10% faster than Ivy Bridge).